通俗理解: 通过与自身有关联的表数据，查询自身表数据

跨多张表查询自身的数据的前提是，这多张表必须有关联

通过 .filter(xxx__xxx='xxx') 实现

1.表的结构

# models.py

from django.db import models

# 书

class Book(models.Model):

    title = models.CharField(max_length=32, verbose_name='书名')

    publish_date = models.DateField(auto_now_add=True, verbose_name='出版日期')

    price = models.DecimalField(max_digits=5, decimal_places=2, verbose_name='价格')

    memo = models.TextField(null=True, verbose_name='说明')

# 创建外键，关联publish

    publisher = models.ForeignKey(to='Publisher', verbose_name='出版社')

# 创建多对多关联author

    author = models.ManyToManyField(to='Author', verbose_name='作者')

    def __str__(self):

        return self.title

    class Meta:

        verbose_name = "书籍"

        verbose_name_plural = verbose_name

# 出版社

class Publisher(models.Model):

    name = models.CharField(max_length=32, verbose_name='出版社名称')

    city = models.CharField(max_length=32, verbose_name='地址')

    def __str__(self):

        return self.name

    class Meta:

        verbose_name = "出版社"

        verbose_name_plural = verbose_name

# 作者

class Author(models.Model):

    name = models.CharField(max_length=32, verbose_name='姓名')

    age = models.IntegerField(verbose_name='年龄')

    phone = models.CharField(max_length=11, verbose_name='手机号码')

 # 创建一对一关联authorDetail

    detail = models.OneToOneField(to='AuthorDetail', verbose_name='详情')

    def __str__(self):

        return self.name

    class Meta:

        verbose_name = "作者"

        verbose_name_plural = verbose_name

# 作者详情

class AuthorDetail(models.Model):

    addr = models.CharField(max_length=64, verbose_name='地址')

    email = models.EmailField(verbose_name='邮箱')

    def __str__(self):

        return self.addr

    class Meta:

        verbose_name = "作者详情"

        verbose_name_plural = verbose_name

2.正向查询

• 语法: .filter(主表类的外键属性名__从表字段名='xxx', ……)

• 查询出书籍的 作者是yeung 的数据

book_list = Book.objects.filter(author__name='yeung')

• 查询出书籍的 作者是yeung，出版社是东莞出版社 的数据

book_list = Book.objects.filter(author__name='yeung').filter(publisher__name='东莞出版社')

# 等同于

book_list = Book.objects.filter(author__name='yeung', publisher__name='东莞出版社')

3. 反向查询

• 语法:

• 如果没有设置表类中外键属性的 related_name

• .filter(主表类名__主表字段名='xxx', ……)

# 查询出书名为西游记的作者

author = Author.objects.filter(book__title='西游记')

• 如果设置了表类中外键属性的 related_name

• .filter(related_name所设置的名字__主表字段名='xxx', ……)

# models.py

class Book(models.Model):

    title = models.CharField(max_length=32, verbose_name='书名')

    publish_date = models.DateField(auto_now_add=True, verbose_name='出版日期')

    price = models.DecimalField(max_digits=5, decimal_places=2, verbose_name='价格')

    memo = models.TextField(null=True, verbose_name='说明')

 # 创建外键，关联publish

    publisher = models.ForeignKey(to='Publisher', verbose_name='出版社')

# 创建多对多关联author

    author = models.ManyToManyField(to='Author', verbose_name='作者', related_name='mf_book')

    def __str__(self):

        return self.title

    class Meta:

        verbose_name = "书籍"

        verbose_name_plural = verbose_name

# 查询出书名为西游记的作者

author = Author.objects.filter(mf_book__title='西游记')