上传番外篇：外键那些事儿的代码和课件

番外篇：外键那些事儿/content_type/admin.py

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+from django.contrib import admin
+from .models import Article, Video, Comment
+
+# Register your models here.
+@admin.register(Article)
+class ArticleAdmin(admin.ModelAdmin):
+    list_display = ['id', 'title', 'content']
+
+@admin.register(Video)
+class VideoAdmin(admin.ModelAdmin):
+    list_display = ['id', 'video_name', 'url']
+
+@admin.register(Comment)
+class CommentAdmin(admin.ModelAdmin):
+    list_display = ['id', 'content_type', 'object_id', 'content_object', 'text']

番外篇：外键那些事儿/content_type/apps.py

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+from django.apps import AppConfig
+
+
+class ContentTypeConfig(AppConfig):
+    name = 'content_type'

番外篇：外键那些事儿/content_type/migrations/0001_initial.py

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+# Generated by Django 2.1.7 on 2019-04-03 07:46
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    initial = True
+
+    dependencies = [
+        ('contenttypes', '0002_remove_content_type_name'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='Article',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('title', models.CharField(max_length=36)),
+                ('content', models.TextField(blank=True)),
+            ],
+        ),
+        migrations.CreateModel(
+            name='Comment',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('object_id', models.PositiveIntegerField()),
+                ('text', models.TextField()),
+                ('content_type', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to='contenttypes.ContentType')),
+            ],
+        ),
+        migrations.CreateModel(
+            name='Video',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('video_name', models.CharField(max_length=36)),
+                ('url', models.URLField()),
+            ],
+        ),
+    ]

番外篇：外键那些事儿/content_type/models.py

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+from django.db import models
+from django.contrib.contenttypes.fields import GenericForeignKey, GenericRelation
+from django.contrib.contenttypes.models import ContentType
+
+# Create your models here.
+# 文章表
+class Article(models.Model):
+    title = models.CharField(max_length=36)
+    content = models.TextField(blank=True)
+    # comments = GenericRelation('Comment')  # 由于Comment后面才定义，所以用字符串惰性引用
+
+    def __str__(self):
+        return '<Article: {0}>'.format(self.title)
+
+    __unicode__ = __str__
+
+# 视频表
+class Video(models.Model):
+    video_name = models.CharField(max_length=36)
+    url = models.URLField()
+
+    def __str__(self):
+        return '<Video: {0}>'.format(self.video_name)
+
+    __unicode__ = __str__
+
+# 评论表
+class Comment(models.Model):
+    # 无法同时指向多个对象
+    # article = models.ForeignKey(Article, on_delete=models.CASCADE)
+    # video = models.ForeignKey(Video, on_delete=models.CASCADE)
+
+    # 万能关系
+    content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)  # 记录关联对象的类型
+    object_id = models.PositiveIntegerField()  # 记录关联对象的主键值
+    content_object = GenericForeignKey('content_type', 'object_id')  # 常规字段，便于使用
+
+    # 评论内容
+    text = models.TextField()
+
+    def __str__(self):
+        return '<Comment: {0}>'.format(self.text)
+
+    __unicode__ = __str__
+
+    # 正向，使用content_object可直接访问
+    '''
+    comment = Comment.objects.first()
+    obj = comment.content_object  # 直接得到所被评论的对象
+    '''
+
+    # 反向，无法直接从其他对象找到Comment对应的评论
+    '''
+    from django.contrib.contenttypes.models import ContentType
+
+    article = Article.objects.first()
+    article_content_type = ContentType.objects.get_for_model(article)
+
+    # 通过Comment自身的筛选查询得到
+    comments = Comment.objects.filter(content_type=article_content_type, object_id=article.pk)
+    '''
+
+    # 反向，方法2，主动建立关系
+    # 参考：https://docs.djangoproject.com/en/2.2/ref/contrib/contenttypes/#reverse-generic-relations
+    '''
+    from django.contrib.contenttypes.fields import GenericRelation
+    # 对应模型加入 comments = GenericRelation('Comment') 字段
+
+    article = Article.objects.first()
+    comments = article.comments.all()
+    '''
+
+
+# content type 官方文档
+# https://docs.djangoproject.com/en/2.2/ref/contrib/contenttypes/
+
+# 更多可以参考，我的Django2.0教程，第22课 评论功能设计和用户登录
+# 链接：https://www.bilibili.com/video/av21029850

番外篇：外键那些事儿/content_type/tests.py

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+from django.test import TestCase
+
+# Create your tests here.

番外篇：外键那些事儿/content_type/views.py

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+from django.shortcuts import render
+
+# Create your views here.

番外篇：外键那些事儿/foreign_key/admin.py

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+from django.contrib import admin
+from .models import SchoolClass, Student
+
+# Register your models here.
+@admin.register(SchoolClass)
+class SchoolClassAdmin(admin.ModelAdmin):
+    list_display = ['id', 'class_name', 'class_master']
+
+@admin.register(Student)
+class StudentAdmin(admin.ModelAdmin):
+    list_display = ['id', 'school_class', 'student_name', 'sex']

番外篇：外键那些事儿/foreign_key/apps.py

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+from django.apps import AppConfig
+
+
+class ForeignKeyConfig(AppConfig):
+    name = 'foreign_key'

番外篇：外键那些事儿/foreign_key/migrations/0001_initial.py

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+# Generated by Django 2.1.7 on 2019-04-03 05:35
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    initial = True
+
+    dependencies = [
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='SchoolClass',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('class_name', models.CharField(max_length=12)),
+                ('class_master', models.CharField(max_length=12)),
+            ],
+        ),
+        migrations.CreateModel(
+            name='Student',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('student_name', models.CharField(max_length=12)),
+                ('sex', models.IntegerField(choices=[(0, '男'), (1, '女')], default=0)),
+                ('school_class', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to='foreign_key.SchoolClass')),
+            ],
+        ),
+    ]

番外篇：外键那些事儿/foreign_key/models.py

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+from django.db import models
+
+# Create your models here.
+# https://docs.djangoproject.com/en/2.2/ref/models/fields/#module-django.db.models.fields.related
+# 班级表
+class SchoolClass(models.Model):
+    class_name = models.CharField(max_length=12)
+    class_master = models.CharField(max_length=12)
+
+    def __str__(self):
+        return '<SchoolClass: {0}>'.format(self.class_name)
+
+    __unicode__ = __str__
+
+# 学生表
+class Student(models.Model):
+    school_class = models.ForeignKey(SchoolClass, on_delete=models.CASCADE)
+    # （on_delete属性说明）
+    # 必填，对应关联的记录（班级），删除的时候，该记录（学生）怎么处理
+    # 参考：https://docs.djangoproject.com/en/2.2/ref/models/fields/#django.db.models.ForeignKey.on_delete
+
+    # 1、CASCADE, 级联删除。
+    # 当班级删除记录的时候，删除对应的所有学生。确保数据完整
+
+    # 2、PROTECT, 保护。
+    # 当班级删除记录的时候，若有学生关联该班级，则不给删除班级
+
+    # 3、SET_NULL, 设置为NULL。 
+    # 当班级删除记录的时候，若有学生关联该班级，则将这些学生的班级外键字段，值设置为null。
+    # school_class = models.ForeignKey(SchoolClass, on_delete=models.SET_NULL, null=True)  # 需要设置null为True
+
+    # 4、SET_DEFAULT，设置为默认值。
+    # def default_class():
+    #     return SchoolClass.objects.first()
+    # school_class = models.ForeignKey(SchoolClass, on_delete=models.SET_DEFAULT, default=default_class)  # 需要设置default
+
+    # 5、SET()，自定义方法，返回一个值，设置该字段的值
+    # 参考：https://docs.djangoproject.com/en/2.2/ref/models/fields/#django.db.models.SET
+
+    # 6、DO_NOTHING，什么时候都不做。
+    # 这个会破坏数据完整性，慎用。
+
+
+    # （正向：顺理成章）
+    # s = Student.objects.first()
+    # s.school_class  # 找到关联的班级对象
+
+    # （反向：冥冥之中）
+    # c = SchoolClass.objects.first()
+    # c.student_set.all()  # xxxx_set 找到被关联的对象
+
+    # related_name，明确关系，班级通过什么属性找到学生
+    # school_class = models.ForeignKey(SchoolClass, on_delete=models.CASCADE, related_name='students')
+    # c = SchoolClass.objects.first()
+    # c.students.all()
+
+
+    # 编辑该字段，直接赋值即可
+    # c = SchoolClass.objects.first()
+    # s = Student()
+    # s.student_name = 'test'
+    # s.school_class = c
+    # s.save()
+
+
+    SEX_CHOICES = (
+        (0, '男'),
+        (1, '女'),
+    )
+    student_name = models.CharField(max_length=12)
+    sex = models.IntegerField(choices=SEX_CHOICES, default=0)
+
+    def __str__(self):
+        return '<Student: {0}>'.format(self.student_name)
+
+    __unicode__ = __str__

番外篇：外键那些事儿/foreign_key/tests.py

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+from django.test import TestCase
+
+# Create your tests here.

番外篇：外键那些事儿/foreign_key/views.py

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+from django.shortcuts import render
+
+# Create your views here.

番外篇：外键那些事儿/manage.py

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+#!/usr/bin/env python
+import os
+import sys
+
+if __name__ == '__main__':
+    os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'relationship.settings')
+    try:
+        from django.core.management import execute_from_command_line
+    except ImportError as exc:
+        raise ImportError(
+            "Couldn't import Django. Are you sure it's installed and "
+            "available on your PYTHONPATH environment variable? Did you "
+            "forget to activate a virtual environment?"
+        ) from exc
+    execute_from_command_line(sys.argv)

番外篇：外键那些事儿/many_to_many/admin.py

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+from django.contrib import admin
+from .models import Author, Book
+
+# Register your models here.
+@admin.register(Author)
+class AuthorAdmin(admin.ModelAdmin):
+    list_display = ['id', 'author_name']
+
+@admin.register(Book)
+class BookAdmin(admin.ModelAdmin):
+    list_display = ['id', 'book_name']
+    filter_horizontal = ('authors',)

番外篇：外键那些事儿/many_to_many/apps.py

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+from django.apps import AppConfig
+
+
+class ManyToManyConfig(AppConfig):
+    name = 'many_to_many'

番外篇：外键那些事儿/many_to_many/migrations/0001_initial.py

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+# Generated by Django 2.1.7 on 2019-04-03 06:11
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    initial = True
+
+    dependencies = [
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='Author',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('author_name', models.CharField(max_length=24)),
+            ],
+        ),
+        migrations.CreateModel(
+            name='Book',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('book_name', models.CharField(max_length=48)),
+                ('authors', models.ManyToManyField(to='many_to_many.Author')),
+            ],
+        ),
+    ]