The Django Book

372 Pages·2014·2.65 MB·English

The Definitive Guide to Django:
Web Development Done Right
Adrian Holovaty, Jacob K. Moss
www.djangobook.com
Buy at Amazon
ISBN-10: 1590597257
ISBN-13: 978-1590597255
The Django Book
Table of Contents
1 Introduction to Django....................................................................................................................................1
1.1 What Is a Web Framework?..............................................................................................................1
1.2 The MVC Design Pattern...................................................................................................................2
1.3 Django’s History................................................................................................................................3
1.4 How to Read This Book.....................................................................................................................4
1.4.1 Required Programming Knowledge.........................................................................................5
1.4.2 Required Python Knowledge....................................................................................................5
1.4.3 New Django Features...............................................................................................................5
1.4.4 Getting Help.............................................................................................................................5
1.4.5 What’s Next..............................................................................................................................6
2 Getting Started.................................................................................................................................................7
2.1 Installing Python................................................................................................................................7
2.2 Installing Django................................................................................................................................7
2.2.1 Installing an Official Release...................................................................................................7
2.2.2 Installing Django from Subversion..........................................................................................8
2.3 Setting Up a Database........................................................................................................................8
2.3.1 Using Django with PostgreSQL...............................................................................................9
2.3.2 Using Django with SQLite 3....................................................................................................9
2.3.3 Using Django with MySQL.....................................................................................................9
2.3.4 Using Django Without a Database...........................................................................................9
2.4 Starting a Project..............................................................................................................................10
2.4.1 The Development Server........................................................................................................10
2.5 What’s Next?...................................................................................................................................11
3 The Basics of Dynamic Web Pages...............................................................................................................12
3.1 Your First View: Dynamic Content.................................................................................................12
3.2 Mapping URLs to Views.................................................................................................................13
3.3 How Django Processes a Request....................................................................................................15
3.3.1 How Django Processes a Request: Complete Details............................................................16
3.4 URLconfs and Loose Coupling.......................................................................................................17
3.5 404 Errors.........................................................................................................................................17
3.6 Your Second View: Dynamic URLs................................................................................................18
3.6.1 A Word About Pretty URLs...................................................................................................19
3.6.2 Wildcard URLpatterns...........................................................................................................19
3.7 Django’s Pretty Error Pages.............................................................................................................21
3.8 What’s next?....................................................................................................................................23
4 The Django Template System.......................................................................................................................24
4.1 Template System Basics..................................................................................................................24
4.2 Using the Template System.............................................................................................................25
4.2.1 Creating Template Objects.....................................................................................................25
4.2.2 Rendering a Template............................................................................................................27
4.2.3 Multiple Contexts, Same Template........................................................................................28
4.2.4 Context Variable Lookup.......................................................................................................29
4.2.5 Playing with Context Objects.................................................................................................31
4.3 Basic Template Tags and Filters......................................................................................................32
4.3.1 Tags........................................................................................................................................32
4.3.2 Filters......................................................................................................................................36
4.4 Philosophies and Limitations...........................................................................................................37
4.5 Using Templates in Views...............................................................................................................38
4.6 Template Loading............................................................................................................................39
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4 The Django Template System
4.6.1 render_to_response()..............................................................................................................41
4.6.2 The locals() Trick...................................................................................................................42
4.6.3 Subdirectories in get_template()............................................................................................42
4.6.4 Theinclude Template Tag......................................................................................................43
4.7 Template Inheritance.......................................................................................................................44
4.8 What’s next?....................................................................................................................................47
5 Interacting with a Database: Models...........................................................................................................48
5.1 The “Dumb” Way to Do Database Queries in Views......................................................................48
5.2 The MTV Development Pattern.......................................................................................................49
5.3 Configuring the Database................................................................................................................50
5.4 Your First App.................................................................................................................................52
5.5 Defining Models in Python..............................................................................................................53
5.6 Your First Model.............................................................................................................................54
5.7 Installing the Model.........................................................................................................................55
5.8 Basic Data Access............................................................................................................................57
5.9 Adding Model String Representations.............................................................................................58
5.10 Inserting and Updating Data..........................................................................................................59
5.11 Selecting Objects...........................................................................................................................60
5.11.1 Filtering Data........................................................................................................................61
5.11.2 Retrieving Single Objects.....................................................................................................61
5.11.3 Ordering Data.......................................................................................................................62
5.11.4 Chaining Lookups................................................................................................................63
5.11.5 Slicing Data..........................................................................................................................63
5.12 Deleting Objects.............................................................................................................................64
5.13 Making Changes to a Database Schema........................................................................................64
5.13.1 Adding Fields.......................................................................................................................64
5.13.2 Removing Fields...................................................................................................................66
5.13.3 Removing Many-to-Many Fields.........................................................................................66
5.13.4 Removing Models................................................................................................................66
5.14 What’s Next?.................................................................................................................................67
6 The Django Administration Site...................................................................................................................68
6.1 Activating the Admin Interface.......................................................................................................68
6.2 Using the Admin Interface...............................................................................................................69
6.2.1 Users, Groups, and Permissions.............................................................................................76
6.3 Customizing the Admin Interface....................................................................................................77
6.4 Customizing the Admin Interface’s Look and Feel.........................................................................79
6.5 Customizing the Admin Index Page................................................................................................79
6.6 When and Why to Use the Admin Interface....................................................................................80
6.7 What’s Next?...................................................................................................................................80
7 Form Processing.............................................................................................................................................81
7.1 Search...............................................................................................................................................81
7.2 The “Perfect Form”..........................................................................................................................83
7.3 Creating a Feedback Form...............................................................................................................83
7.4 Processing the Submission...............................................................................................................86
7.5 Custom Validation Rules.................................................................................................................87
7.6 A Custom Look and Feel.................................................................................................................88
7.7 Creating Forms from Models...........................................................................................................89
7.8 What’s Next?...................................................................................................................................90
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8 Advanced Views and URLconfs...................................................................................................................91
8.1 URLconf Tricks...............................................................................................................................91
8.1.1 Streamlining Function Imports...............................................................................................91
8.1.2 Using Multiple View Prefixes................................................................................................92
8.1.3 Special-Casing URLs in Debug Mode...................................................................................93
8.1.4 Using Named Groups.............................................................................................................93
8.1.5 Understanding the Matching/Grouping Algorithm................................................................95
8.1.6 Passing Extra Options to View Functions..............................................................................95
8.1.7 Using Default View Arguments.............................................................................................99
8.1.8 Special-Casing Views...........................................................................................................100
8.1.9 Capturing Text in URLs.......................................................................................................100
8.1.10 Determining What the URLconf Searches Against...........................................................101
8.2 Including Other URLconfs............................................................................................................102
8.2.1 How Captured Parameters Work with include()..................................................................102
8.2.2 How Extra URLconf Options Work with include().............................................................103
8.3 What’s Next?.................................................................................................................................104
9 Generic Views...............................................................................................................................................105
9.1 Using Generic Views.....................................................................................................................105
9.2 Generic Views of Objects..............................................................................................................106
9.3 Extending Generic Views..............................................................................................................107
9.3.1 Making “Friendly” Template Contexts................................................................................107
9.3.2 Adding Extra Context...........................................................................................................108
9.3.3 Viewing Subsets of Objects.................................................................................................109
9.3.4 Complex Filtering with Wrapper Functions.........................................................................110
9.3.5 Performing Extra Work........................................................................................................110
9.4 What’s Next?.................................................................................................................................111
10 Extending the Template Engine...............................................................................................................112
10.1 Template Language Review........................................................................................................112
10.2 RequestContext and Context Processors.....................................................................................112
10.2.1 django.core.context_processors.auth..................................................................................116
10.2.2 django.core.context_processors.debug...............................................................................116
10.2.3 django.core.context_processors.i18n.................................................................................116
10.2.4 django.core.context_processors.request.............................................................................116
10.2.5 Guidelines for Writing Your Own Context Processors......................................................116
10.3 Inside Template Loading.............................................................................................................117
10.4 Extending the Template System..................................................................................................118
10.4.1 Creating a Template Library..............................................................................................118
10.4.2 Writing Custom Template Filters.......................................................................................119
10.4.3 Writing Custom Template Tags.........................................................................................120
10.4.4 Shortcut for Simple Tags....................................................................................................124
10.4.5 Inclusion Tags....................................................................................................................125
10.5 Writing Custom Template Loaders..............................................................................................126
10.6 Using the Built-in Template Reference.......................................................................................127
10.7 Configuring the Template System in Standalone Mode..............................................................128
10.8 What’s Next.................................................................................................................................128
11 Generating Non-HTML Content..............................................................................................................129
11.1 The basics: views and MIME-types.............................................................................................129
11.2 Producing CSV............................................................................................................................130
11.3 Generating PDFs..........................................................................................................................131
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11 Generating Non-HTML Content
11.3.1 Installing ReportLab...........................................................................................................131
11.3.2 Writing Your View.............................................................................................................131
11.3.3 Complex PDFs...................................................................................................................132
11.4 Other Possibilities........................................................................................................................133
11.5 The Syndication Feed Framework...............................................................................................133
11.5.1 Initialization........................................................................................................................134
11.5.2 A Simple Feed....................................................................................................................134
11.5.3 A More Complex Feed.......................................................................................................135
11.5.4 Specifying the Type of Feed..............................................................................................137
11.5.5 Enclosures..........................................................................................................................137
11.5.6 Language............................................................................................................................138
11.5.7 URLs..................................................................................................................................138
11.5.8 Publishing Atom and RSS Feeds in Tandem.....................................................................138
11.6 The Sitemap Framework..............................................................................................................139
11.6.1 Installation..........................................................................................................................139
11.6.2 Initialization........................................................................................................................139
11.6.3 Sitemap Classes..................................................................................................................140
11.6.4 Shortcuts.............................................................................................................................141
11.6.5 Creating a Sitemap Index...................................................................................................142
11.6.6 Pinging Google...................................................................................................................142
11.7 What’s Next?...............................................................................................................................143
12 Sessions, Users, and Registration.............................................................................................................144
12.1 Cookies........................................................................................................................................144
12.1.1 Getting and Setting Cookies...............................................................................................145
12.1.2 The Mixed Blessing of Cookies.........................................................................................146
12.2 Django’s Session Framework......................................................................................................146
12.2.1 Enabling Sessions...............................................................................................................147
12.2.2 Using Sessions in Views....................................................................................................147
12.2.3 Setting Test Cookies...........................................................................................................148
12.2.4 Using Sessions Outside of Views.......................................................................................149
12.2.5 When Sessions Are Saved..................................................................................................149
12.2.6 Browser-Length Sessions vs. Persistent Sessions..............................................................150
12.2.7 Other Session Settings........................................................................................................150
12.3 Users and Authentication.............................................................................................................151
12.3.1 Enabling Authentication Support.......................................................................................151
12.3.2 Using Users........................................................................................................................152
12.3.3 Logging In and Out............................................................................................................153
12.3.4 Limiting Access to Logged-in Users..................................................................................155
12.3.5 Limiting Access to Users Who Pass a Test........................................................................155
12.3.6 Managing Users, Permissions, and Groups........................................................................156
12.3.7 Using Authentication Data in Templates...........................................................................159
12.4 The Other Bits: Permissions, Groups, Messages, and Profiles....................................................160
12.4.1 Permissions.........................................................................................................................160
12.4.2 Groups................................................................................................................................161
12.4.3 Messages............................................................................................................................161
12.4.4 Profiles................................................................................................................................162
12.5 What’s Next.................................................................................................................................162
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13 Caching.......................................................................................................................................................163
13.1 Setting Up the Cache...................................................................................................................163
13.1.1 Memcached........................................................................................................................163
13.1.2 Database Caching...............................................................................................................164
13.1.3 Filesystem Caching............................................................................................................165
13.1.4 Local-Memory Caching.....................................................................................................165
13.1.5 Simple Caching (for Development)...................................................................................165
13.1.6 Dummy Caching (for Development)..................................................................................165
13.1.7 CACHE_BACKEND Arguments......................................................................................166
13.2 The Per-Site Cache......................................................................................................................166
13.3 The Per-View Cache....................................................................................................................167
13.3.1 Specifying Per-View Cache in the URLconf.....................................................................168
13.4 The Low-Level Cache API..........................................................................................................168
13.5 Upstream Caches.........................................................................................................................169
13.5.1 Using Vary Headers...........................................................................................................170
13.5.2 Other Cache Headers..........................................................................................................171
13.6 Other Optimizations.....................................................................................................................172
13.7 Order of MIDDLEWARE_CLASSES........................................................................................172
13.8 What’s Next?...............................................................................................................................173
14 Other Contributed Subframeworks.........................................................................................................174
14.1 The Django Standard Library......................................................................................................174
14.2 Sites..............................................................................................................................................175
14.2.1 Scenario 1: Reusing Data on Multiple Sites.......................................................................175
14.2.2 Scenario 2: Storing Your Site Name/Domain in One Place...............................................175
14.2.3 How to Use the Sites Framework.......................................................................................175
14.2.4 The Sites Framework’s Capabilities...................................................................................176
14.2.5 CurrentSiteManager...........................................................................................................178
14.2.6 How Django Uses the Sites Framework.............................................................................179
14.3 Flatpages......................................................................................................................................180
14.3.1 Using Flatpages..................................................................................................................180
14.3.2 Adding, Changing, and Deleting Flatpages........................................................................181
14.3.3 Using Flatpage Templates..................................................................................................182
14.4 Redirects......................................................................................................................................182
14.4.1 Using the Redirects Framework.........................................................................................182
14.4.2 Adding, Changing, and Deleting Redirects........................................................................183
14.5 CSRF Protection..........................................................................................................................184
14.5.1 A Simple CSRF Example...................................................................................................184
14.5.2 A More Complex CSRF Example......................................................................................184
14.5.3 Preventing CSRF................................................................................................................184
14.6 Humanizing Data.........................................................................................................................186
14.6.1 apnumber............................................................................................................................186
14.6.2 intcomma............................................................................................................................186
14.6.3 intword................................................................................................................................186
14.6.4 ordinal.................................................................................................................................186
14.7 Markup Filters..............................................................................................................................187
14.8 What’s Next?...............................................................................................................................187
15 Middleware.................................................................................................................................................188
15.1 What’s Middleware?....................................................................................................................188
15.2 Middleware Installation...............................................................................................................189
15.3 Middleware Methods...................................................................................................................189
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15 Middleware
15.3.1 Initializer: __init__(self).....................................................................................................189
15.3.2 Request Preprocessor: process_request(self, request)........................................................190
15.3.3 View Preprocessor: process_view(self, request, view, args, kwargs)................................190
15.3.4 Response Postprocessor: process_response(self, request, response).................................190
15.3.5 Exception Postprocessor: process_exception(self, request, exception).............................191
15.4 Built-in Middleware.....................................................................................................................191
15.4.1 Authentication Support Middleware..................................................................................191
15.4.2 “Common” Middleware.....................................................................................................191
15.4.3 Compression Middleware...................................................................................................192
15.4.4 Conditional GET Middleware............................................................................................192
15.4.5 Reverse Proxy Support (X-Forwarded-For Middleware)..................................................192
15.4.6 Session Support Middleware..............................................................................................193
15.4.7 Sitewide Cache Middleware...............................................................................................193
15.4.8 Transaction Middleware.....................................................................................................193
15.4.9 “X-View” Middleware.......................................................................................................193
15.5 What’s Next?...............................................................................................................................193
16 Integrating with Legacy Databases and Applications............................................................................194
16.1 Integrating with a Legacy Database.............................................................................................194
16.1.1 Usinginspectdb..................................................................................................................194
16.1.2 Cleaning Up Generated Models.........................................................................................194
16.2 Integrating with an Authentication System..................................................................................195
16.2.1 Specifying Authentication Back-ends................................................................................196
16.2.2 Writing an Authentication Back-end..................................................................................196
16.3 Integrating with Legacy Web Applications.................................................................................197
16.4 What’s Next?...............................................................................................................................198
17 Extending Django’s Admin Interface......................................................................................................199
17.1 The Zen of Admin........................................................................................................................200
17.1.1 “Trusted users …”..............................................................................................................200
17.1.2 “… editing …”...................................................................................................................200
17.1.3 “… structured content”.......................................................................................................200
17.1.4 Full Stop.............................................................................................................................200
17.2 Customizing Admin Templates...................................................................................................201
17.2.1 Custom Model Templates..................................................................................................202
17.2.2 Custom JavaScript..............................................................................................................203
17.3 Creating Custom Admin Views...................................................................................................203
17.4 Overriding Built-in Views...........................................................................................................205
17.5 What’s Next?...............................................................................................................................206
18 Internationalization...................................................................................................................................207
18.1 Specifying Translation Strings in Python Code...........................................................................208
18.1.1 Standard Translation Functions..........................................................................................208
18.1.2 Marking Strings As No-op.................................................................................................209
18.1.3 Lazy Translation.................................................................................................................209
18.1.4 Pluralization........................................................................................................................209
18.2 Specifying Translation Strings in Template Code.......................................................................210
18.3 Creating Language Files..............................................................................................................211
18.3.1 Creating Message Files......................................................................................................211
18.3.2 Compiling Message Files...................................................................................................213
18.4 How Django Discovers Language Preference.............................................................................213
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18 Internationalization
18.5 The set_language Redirect View.................................................................................................215
18.6 Using Translations in Your Own Projects...................................................................................215
18.7 Translations and JavaScript.........................................................................................................216
18.7.1 The javascript_catalog View..............................................................................................216
18.7.2 Using the JavaScript Translation Catalog..........................................................................217
18.7.3 Creating JavaScript Translation Catalogs..........................................................................218
18.8 Notes for Users Familiar withgettext..........................................................................................218
18.9 What’s Next?...............................................................................................................................218
19 Security.......................................................................................................................................................219
19.1 The Theme of Web Security........................................................................................................219
19.2 SQL Injection...............................................................................................................................219
19.2.1 The Solution.......................................................................................................................220
19.3 Cross-Site Scripting (XSS)..........................................................................................................221
19.3.1 The Solution.......................................................................................................................222
19.4 Cross-Site Request Forgery.........................................................................................................222
19.5 Session Forging/Hijacking...........................................................................................................222
19.5.1 The Solution.......................................................................................................................223
19.6 Email Header Injection................................................................................................................224
19.6.1 The Solution.......................................................................................................................224
19.7 Directory Traversal......................................................................................................................224
19.7.1 The Solution.......................................................................................................................225
19.8 Exposed Error Messages..............................................................................................................225
19.8.1 The Solution.......................................................................................................................226
19.9 A Final Word on Security............................................................................................................226
19.10 What’s Next...............................................................................................................................226
20 Deploying Django.......................................................................................................................................227
20.1 Shared Nothing............................................................................................................................227
20.2 A Note on Personal Preferences..................................................................................................228
20.3 Using Django with Apache and mod_python..............................................................................229
20.3.1 Basic Configuration............................................................................................................229
20.3.2 Running Multiple Django Installations on the Same Apache Instance..............................230
20.3.3 Running a Development Server with mod_python............................................................231
20.3.4 Serving Django and Media Files from the Same Apache Instance....................................231
20.3.5 Error Handling....................................................................................................................232
20.3.6 Handling a Segmentation Fault..........................................................................................232
20.4 Using Django with FastCGI........................................................................................................233
20.4.1 FastCGI Overview..............................................................................................................233
20.4.2 Running Your FastCGI Server...........................................................................................233
20.4.3 Using Django with Apache and FastCGI...........................................................................234
20.4.4 FastCGI and lighttpd..........................................................................................................235
20.4.5 Running Django on a Shared-Hosting Provider with Apache...........................................236
20.5 Scaling.........................................................................................................................................237
20.5.1 Running on a Single Server................................................................................................237
20.5.2 Separating Out the Database Server...................................................................................238
20.5.3 Running a Separate Media Server......................................................................................239
20.5.4 Implementing Load Balancing and Redundancy...............................................................239
20.5.5 Going Big...........................................................................................................................241
20.6 Performance Tuning.....................................................................................................................241
20.6.1 There’s No Such Thing As Too Much RAM.....................................................................242
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20 Deploying Django
20.6.2 Turn Off Keep-Alive..........................................................................................................242
20.6.3 Use memcached..................................................................................................................242
20.6.4 Use memcached Often........................................................................................................242
20.6.5 Join the Conversation.........................................................................................................242
20.7 What’s Next?...............................................................................................................................243
21 Appendix A: Case Studies.........................................................................................................................244
21.1 Cast of Characters........................................................................................................................244
21.2 Why Django?...............................................................................................................................245
21.3 Getting Started.............................................................................................................................246
21.4 Porting Existing Code..................................................................................................................246
21.5 How Did It Go?............................................................................................................................247
21.6 Team Structure.............................................................................................................................248
21.7 Deployment..................................................................................................................................249
22 Appendix B: Model Definition Reference................................................................................................251
22.1 Fields............................................................................................................................................251
22.1.1 AutoField............................................................................................................................251
22.1.2 BooleanField......................................................................................................................252
22.1.3 CharField............................................................................................................................252
22.1.4 CommaSeparatedIntegerField............................................................................................252
22.1.5 DateField............................................................................................................................252
22.1.6 DateTimeField....................................................................................................................252
22.1.7 EmailField..........................................................................................................................252
22.1.8 FileField..............................................................................................................................252
22.1.9 FilePathField......................................................................................................................253
22.1.10 FloatField..........................................................................................................................254
22.1.11 ImageField........................................................................................................................254
22.1.12 IntegerField......................................................................................................................254
22.1.13 IPAddressField.................................................................................................................254
22.1.14 NullBooleanField.............................................................................................................254
22.1.15 PhoneNumberField...........................................................................................................254
22.1.16 PositiveIntegerField..........................................................................................................255
22.1.17 PositiveSmallIntegerField................................................................................................255
22.1.18 SlugField..........................................................................................................................255
22.1.19 SmallIntegerField.............................................................................................................255
22.1.20 TextField..........................................................................................................................255
22.1.21 TimeField.........................................................................................................................255
22.1.22 URLField..........................................................................................................................255
22.1.23 USStateField.....................................................................................................................255
22.1.24 XMLField.........................................................................................................................256
22.2 Universal Field Options...............................................................................................................256
22.2.1 null......................................................................................................................................256
22.2.2 blank...................................................................................................................................256
22.2.3 choices................................................................................................................................256
22.2.4 db_column..........................................................................................................................257
22.2.5 db_index.............................................................................................................................257
22.2.6 editable...............................................................................................................................257
22.2.7 help_text.............................................................................................................................257
22.2.8 primary_key........................................................................................................................257
22.2.9 radio_admin........................................................................................................................258
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22 Appendix B: Model Definition Reference
22.2.10 unique...............................................................................................................................258
22.2.11 unique_for_date................................................................................................................258
22.2.12 unique_for_month............................................................................................................258
22.2.13 unique_for_year................................................................................................................258
22.2.14 verbose_name...................................................................................................................258
22.3 Relationships................................................................................................................................259
22.3.1 Many-to-One Relationships...............................................................................................259
22.3.2 Many-to-Many Relationships.............................................................................................261
22.4 Model Metadata Options..............................................................................................................262
22.4.1 db_table..............................................................................................................................262
22.4.2 get_latest_by.......................................................................................................................263
22.4.3 order_with_respect_to........................................................................................................263
22.4.4 ordering..............................................................................................................................263
22.4.5 permissions.........................................................................................................................264
22.4.6 unique_together..................................................................................................................264
22.4.7 verbose_name.....................................................................................................................264
22.4.8 verbose_name_plural..........................................................................................................265
22.5 Managers......................................................................................................................................265
22.5.1 Manager Names..................................................................................................................265
22.5.2 Custom Managers...............................................................................................................265
22.6 Model Methods............................................................................................................................267
22.6.1 __str__................................................................................................................................268
22.6.2 get_absolute_url.................................................................................................................268
22.6.3 Executing Custom SQL......................................................................................................269
22.6.4 Overriding Default Model Methods...................................................................................270
22.7 Admin Options.............................................................................................................................270
22.7.1 date_hierarchy....................................................................................................................270
22.7.2 fields...................................................................................................................................271
22.7.3 js.........................................................................................................................................272
22.7.4 list_display..........................................................................................................................272
22.7.5 list_display_links................................................................................................................273
22.7.6 list_filter.............................................................................................................................274
22.7.7 list_per_page......................................................................................................................274
22.7.8 list_select_related...............................................................................................................274
22.7.9 ordering..............................................................................................................................274
22.7.10 save_as..............................................................................................................................275
22.7.11 save_on_top......................................................................................................................275
22.7.12 search_fields.....................................................................................................................275
23 Appendix C: Database API Reference.....................................................................................................277
23.1 Creating Objects...........................................................................................................................277
23.1.1 What Happens When You Save?.......................................................................................278
23.1.2 Autoincrementing Primary Keys........................................................................................278
23.2 Saving Changes to Objects..........................................................................................................279
23.3 Retrieving Objects.......................................................................................................................279
23.4 Caching and QuerySets................................................................................................................280
23.5 Filtering Objects..........................................................................................................................281
23.5.1 Chaining Filters..................................................................................................................281
23.5.2 Limiting QuerySets............................................................................................................282
23.5.3 Query Methods That Return New QuerySets.....................................................................283
23.5.4 QuerySet Methods That Do Not Return QuerySets...........................................................286
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