字段对象: Model类（表类）中的字段类所实例化出来的对象

获取字段对象的方法在《ORM-_meta的用法》章节中有提到

1.该章节中所用到的表

# models.py

from django.db import models

class Book(models.Model):

    title = models.CharField(max_length=15, verbose_name='书名')

    price = models.IntegerField(verbose_name='价格')

    publish = models.ForeignKey(to='Publish', verbose_name='出版社')

    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

class Publish(models.Model):

    title = models.CharField(max_length=15)

    def __str__(self):

        return self.title

    class Meta:

        verbose_name = '出版社'

        verbose_name_plural = verbose_name

class Author(models.Model):

    name = models.CharField(max_length=15)

    def __str__(self):

        return self.name

    class Meta:

        verbose_name = '作者'

        verbose_name_plural = verbose_name

2. rel.to -> 获取该字段对象下所关联的模型表（即: 表类）

• 语法: 字段对象.rel.to

• rel.to 只作用于 一对一、一对多、多对多字段

# 获取字段对象

field_obj = Book._meta.get_field('publish')

# 获取该字段对象下所关联的模型表

publish_class = field_obj.rel.to  # <class 'app01.models.Publish'>

# 获取该模型表下的数据

publish_data = publish_class.objects.all()  # <QuerySet [<Publish: 东莞出版社>, <Publish: 广州出版社>]>

# 等同于

publish_data = field_obj.rel.to.objects.all()  # <QuerySet [<Publish: 东莞出版社>, <Publish: 广州出版社>]>