字段参数
# CharField(max_length=None, min_length=None, allow_blank=False, trim_whitespace=True)
    max_length :校验，最大长度
    min_length：校验最短长度
    allow_blank：是否允许为空
    trim_whitespace：去掉前后的空白
    
    
# DateTimeField(format=api_settings.DATETIME_FORMAT)
    format:格式化成的样子
    
# IntegerField(max_value=None, min_value=None)
    max_value ：数字
    min_value：数字
  

### 通用参数---》所有字段类上都可以加
read_only    表明该字段仅用于序列化输出，默认False
write_only    表明该字段仅用于反序列化输入，默认False
-------------------------------------------------------
required    表明该字段在反序列化时必须输入，默认True
default         反序列化时使用的默认值
allow_null     表明该字段是否允许传入None，默认False
validators     该字段使用的验证器：validators=[方法]，方法对该字段做校验
error_messages    包含错误编号与错误信息的字典
---------------
label         用于HTML展示API页面时，显示的字段名称
help_text     用于HTML展示API页面时，显示的字段帮助提示信息


# 字段校验有四层
    -1 字段自己
    -2 validators校验  忽略
    -3 局部钩子
    -4 全局钩子

# 定制序列化返回的字段格式
    -方案一：在表模型中写，在序列化类中映射  （可以使用source）
        # models.py
        def publish_detail(self):
            return {'name': self.publish.name, 'city': self.publish.city}
        # serializer.py
            publish_detail = serializers.DictField()
        # 前端看到
            "publish_detail": {
                "name": "北京出版本是",
                "city": "北京"
            }
    -方案二：在序列化类中写SerializerMethodField，必须配合一个方法 get_字段名，方法返回什么，前端就看到什么
        # Serializer.py
            publish_detail = serializers.SerializerMethodField()
            def get_publish_detail(self, obj):
                return {'name': obj.publish.name, 'city': obj.publish.city}
        # 前端看到
            "publish_detail": {
                "name": "北京出版本是",
                "city": "北京"
            }

models.py
from django.db import models


class Book(models.Model):
    name = models.CharField(max_length=32)
    price = models.DecimalField(max_digits=5, decimal_places=2)

    publish = models.ForeignKey(to='Publish', on_delete=models.CASCADE)
    authors = models.ManyToManyField(to='Author')

    def __str__(self):
        return self.name
    # def book_name(self):
    #     return self.name+'sb'
    # def publish_detail(self):
    #     return {'name': self.publish.name, 'city': self.publish.city}
    #
    # def author_list(self):
    #     l = []
    #     for author in self.authors.all():
    #         l.append({'name': author.name, 'age': author.age})
    #     return l


class Author(models.Model):
    name = models.CharField(max_length=32)
    age = models.IntegerField()
    author_detail = models.OneToOneField(to='AuthorDetail', on_delete=models.CASCADE)

    def __str__(self):
        return self.name


class AuthorDetail(models.Model):
    telephone = models.BigIntegerField()
    birthday = models.DateField()
    addr = models.CharField(max_length=64)


class Publish(models.Model):
    name = models.CharField(max_length=32)
    city = models.CharField(max_length=32)
    email = models.EmailField()

    def __str__(self):
        return self.name

    class Meta:
        verbose_name = '出版社'
        verbose_name_plural = verbose_name

class BookView(APIView):
    def get(self, request):
        obj = Book.objects.all()
        ser = BookSerializer(instance=obj, many=True)

        '''
        [
            {
                "name": "西游记",
                "price": "66.00",
                "publish_detail": {name:名字,city:城市}，
                "authors_list":[{name:名字,age:19}]
            },
    
        ]
        
        '''
        return Response(ser.data)

### 定制返回字段
class BookSerializer(serializers.Serializer):
    name = serializers.CharField()
    price = serializers.CharField()
    #### 定制返回字段---》方案一：在表模型中写方法，在序列化类中做映射
    # publish_detail = serializers.CharField()  # publish_detail 会映射表模型中 publish_detail方法，方法返回值是 字典，强行用CharField字符串接收
    # publish_detail = serializers.DictField()  # publish_detail 会映射表模型中 publish_detail方法，方法返回值是 字典，用DictField接收
    # author_list = serializers.ListField()

    ###定制返回字段---》方案二：在序列化类中写  SerializerMethodField
    # 只要写了这个字段类SerializerMethodField，必须配合一个方法：get_字段名，这个方法返回什么，前端这个字段就显示什么
    publish_detail = serializers.SerializerMethodField()

    def get_publish_detail(self, obj):
        # 当前序列化到的book对象
        return {'name': obj.publish.name, 'city': obj.publish.city}

    author_list = serializers.SerializerMethodField()

    def get_author_list(self, obj):
        l = []
        for author in obj.authors.all():
            l.append({'name': author.name, 'age': author.age})
        return l

    book_name = serializers.SerializerMethodField()
    
    def get_book_name(self, obj):
        return obj.name + 'sb'

class BookSerializer(serializers.Serializer):
    name = serializers.CharField()  # 公共的
    price = serializers.CharField()  # 公共的
    publish = serializers.IntegerField(write_only=True)  # 只用来做反序列化
    authors = serializers.ListField(write_only=True)  # 只用来做反序列化

    publish_detail = serializers.SerializerMethodField(read_only=True)  # 只用来做序列化
    author_list = serializers.SerializerMethodField(read_only=True)  # 只用来做序列化

    def get_publish_detail(self, obj):
        return {'name': obj.publish.name, 'city': obj.publish.city}

    def get_author_list(self, obj):
        l = []
        for author in obj.authors.all():
            l.append({'name': author.name, 'age': author.age})
        return l

    def create(self, validated_data):
        # {name,price,publish:1,authors:[1,2]}
        authors = validated_data.pop('authors')
        book = Book.objects.create(name=validated_data.get('name'), price=validated_data.get('price'),
                                   publish_id=validated_data.get('publish'))
        book.authors.add(*authors)
        return book

    def update(self, instance, validated_data):
        # {name,price,publish:1,authors:[1,2]}
        authors = validated_data.pop('authors')
        validated_data['publish_id'] = validated_data.pop('publish')
        for key in validated_data:
            setattr(instance, key, validated_data[key])

        instance.save()
        # 先清空在放入
        # instance.authors.clear()
        # instance.authors.add(*authors)
        # 直接存
        instance.authors.set(authors)
        return instance

class BookView(APIView):

    def post(self, request):
        ser = BookSerializer(data=request.data)
        if ser.is_valid():
            ser.save()
            return Response(ser.data)
        else:
            return Response(ser.errors)


class BookDetail(APIView):
    def put(self, request, pk):
        book = Book.objects.filter(pk=pk).first()
        ser = BookSerializer(instance=book, data=request.data)
        if ser.is_valid():
            ser.save()
            return Response(ser.data)
        else:
            return Response(ser.errors)

继承ModelSerializer--->少写代码
class BookSerializer(serializers.ModelSerializer):
    # name = serializers.CharField(max_length=18,min_length=3)  # 公共的
    # price = serializers.CharField()  # 公共的
    # publish = serializers.IntegerField(write_only=True)  # 只用来做反序列化
    # authors = serializers.ListField(write_only=True)  # 只用来做反序列化
    # 上述操作，通过 Meta实现了

    # 扩写的字段，也要在fields注册
    # 方式二：定制字段
    # publish_detail = serializers.SerializerMethodField(read_only=True)  # 只用来做序列化
    # author_list = serializers.SerializerMethodField(read_only=True)  # 只用来做序列化
    # def get_publish_detail(self, obj):
    #     return {'name': obj.publish.name, 'city': obj.publish.city}
    # def get_author_list(self, obj):
    #     l = []
    #     for author in obj.authors.all():
    #         l.append({'name': author.name, 'age': author.age})
    #     return l

    # 方式二：定制字段方式一
    # publish_detail = serializers.DictField(read_only=True)
    # author_list = serializers.ListField(read_only=True)
    class Meta:
        model = Book  # 写了这两句，会把表模型中Book，所有字段映射过来
        # fields='__all__'
        fields = ['name', 'price', 'publish', 'authors', 'publish_detail', 'author_list']
        extra_kwargs = {  # 给某个或某几个字段设置字段属性
            'name': {'max_length': 18, 'min_length': 3},
            'publish': {'write_only': True},
            'authors': {'write_only': True},
            'publish_detail': {'read_only': True},
            'author_list': {'read_only': True},
        }

    # 一般不需要写create和update了---》ModelSerializer帮咱们实现了
    # 局部钩子和全局钩子，该怎么写还怎么写
    # def validate_name(self,name):
    #     pass