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django rest_framework 序列化组件详解

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12/02
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为什么要用序列化组件

当我们做前后端分离的项目,我们前后端交互一般都选择JSON数据格式，JSON是一个轻量级的数据交互格式。

那么我们给前端数据的时候都要转成json格式，那就需要对我们从数据库拿到的数据进行序列化。

接下来我们看下django序列化和rest_framework序列化的对比

Django的序列化方法 
class BooksView(View):

    def get(self, request):

        book_list = Book.objects.values("id", "title", "chapter", "pub_time", "publisher")

        book_list = list(book_list)

        # 如果我们需要取外键关联的字段信息 需要循环获取外键 再去数据库查然后拼接成我们想要的

        ret = []

        for book in book_list:

            pub_dict = {}

            pub_obj = Publish.objects.filter(pk=book["publisher"]).first()

            pub_dict["id"] = pub_obj.pk

            pub_dict["title"] = pub_obj.title

            book["publisher"] = pub_dict

            ret.append(book)

        ret = json.dumps(book_list, ensure_ascii=False, cls=MyJson)

        return HttpResponse(ret)

# json.JSONEncoder.default()

# 解决json不能序列化时间字段的问题

class MyJson(json.JSONEncoder):

    def default(self, field):

        if isinstance(field, datetime.datetime):

            return field.strftime('%Y-%m-%d %H:%M:%S')

        elif isinstance(field, datetime.date):

            return field.strftime('%Y-%m-%d')

        else:

            return json.JSONEncoder.default(self, field)


from django.core import serializers

# 能够得到我们要的效果 结构有点复杂

class BooksView(View):

    def get(self, request):

        book_list = Book.objects.all()

        ret = serializers.serialize("json", book_list)

        return HttpResponse(ret)

DRF序列化的方法

首先，我们要用DRF的序列化，就要遵循人家框架的一些标准，

  • Django我们CBV继承类是View，现在DRF我们要用APIView

  • Django中返回的时候我们用HTTPResponse，JsonResponse，render ，DRF我们用Response

为什么这么用~我们之后会详细讲我们继续来看序列化

序列化

serializer: 

class BookSerializer(serializers.Serializer):

    id = serializers.IntegerField()

    title = serializers.CharField(max_length=32)

    CHOICES = ((1, "Linux"), (2, "Django"), (3, "Python"))

    chapter = serializers.ChoiceField(choices=CHOICES, source="get_chapter_display")

    pub_time = serializers.DateField()

view: 

from rest_framework.views import APIView

from rest_framework.response import Response

class BookView(APIView):

    def get(self, request):

        book_list = Book.objects.all()

        ret = BookSerializer(book_list, many=True)

        return Response(ret.data)

外键关系的序列化 

from rest_framework import serializers

from .models import Book

class PublisherSerializer(serializers.Serializer):

    id = serializers.IntegerField(read_only=True)

    title = serializers.CharField(max_length=32)

class UserSerializer(serializers.Serializer):

    id = serializers.IntegerField(read_only=True)

    name = serializers.CharField(max_length=32)

    age = serializers.IntegerField()

class BookSerializer(serializers.Serializer):

    id = serializers.IntegerField(read_only=True)

    title = serializers.CharField(max_length=32)

    CHOICES = ((1, "Linux"), (2, "Django"), (3, "Python"))

    chapter = serializers.ChoiceField(choices=CHOICES, source="get_chapter_display", read_only=True)

    pub_time = serializers.DateField()

    publisher = PublisherSerializer(read_only=True)

    user = UserSerializer(many=True, read_only=True)

反序列化

当前端给我们发post的请求的时候,我们要进行一些校验然后保存到数据库

这些校验以及保存工作，DRF的Serializer也给我们提供了一些方法了

首先 我们要写反序列化用的一些字段 有些字段要跟序列化区分开

Serializer提供了.is_valid() 和.save()方法

serializers: 

# serializers.py 文件

class BookSerializer(serializers.Serializer):

    id = serializers.IntegerField(read_only=True)

    title = serializers.CharField(max_length=32)

    CHOICES = ((1, "Linux"), (2, "Django"), (3, "Python"))

    chapter = serializers.ChoiceField(choices=CHOICES, source="get_chapter_display", read_only=True)

    w_chapter = serializers.IntegerField(write_only=True)

    pub_time = serializers.DateField()

    publisher = PublisherSerializer(read_only=True)

    user = UserSerializer(many=True, read_only=True)

    users = serializers.ListField(write_only=True)

    publisher_id = serializers.IntegerField(write_only=True)

    def create(self, validated_data):

        book = Book.objects.create(title=validated_data["title"], chapter=validated_data["w_chapter"], pub_time=validated_data["pub_time"],                                  publisher_id=validated_data["publisher_id"])

        book.user.add(*validated_data["users"])

        return book

view: 

class BookView(APIView):

    def get(self, request):

        book_list = Book.objects.all()

        ret = BookSerializer(book_list, many=True)

        return Response(ret.data)

    def post(self, request):

        # book_obj = request.data

        print(request.data)

        serializer = BookSerializer(data=request.data)

        if serializer.is_valid():

            print(12341253)

            serializer.save()

            return Response(serializer.validated_data)

        else:

            return Response(serializer.errors)

当前端给我们发送patch请求的时候，前端传给我们用户要更新的数据，我们要对数据进行部分验证~~

Serializer: 

class BookSerializer(serializers.Serializer):

    id = serializers.IntegerField(read_only=True)

    title = serializers.CharField(max_length=32)

    CHOICES = ((1, "Linux"), (2, "Django"), (3, "Python"))

    chapter = serializers.ChoiceField(choices=CHOICES, source="get_chapter_display", read_only=True)

    w_chapter = serializers.IntegerField(write_only=True)

    pub_time = serializers.DateField()

    publisher = PublisherSerializer(read_only=True)

    user = UserSerializer(many=True, read_only=True)

    users = serializers.ListField(write_only=True)

    publisher_id = serializers.IntegerField(write_only=True)

    def create(self, validated_data):

        book = Book.objects.create(title=validated_data["title"], chapter=validated_data["w_chapter"], pub_time=validated_data["pub_time"],

                                   publisher_id=validated_data["publisher_id"])

        book.user.add(*validated_data["users"])

        return book

    def update(self, instance, validated_data):

        instance.title = validated_data.get("title", instance.title)

        instance.chapter = validated_data.get("w_chapter", instance.chapter)

        instance.pub_time = validated_data.get("pub_time", instance.pub_time)

        instance.publisher_id = validated_data.get("publisher_id", instance.publisher_id)

        if validated_data.get("users"):

            instance.user.set(validated_data.get("users"))

        instance.save()

        return instance

view: 

class BookView(APIView):

     def patch(self, request):

        print(request.data)

        book_id = request.data["id"]

        book_info = request.data["book_info"]

        book_obj = Book.objects.filter(pk=book_id).first()

        serializer = BookSerializer(book_obj, data=book_info, partial=True)

        if serializer.is_valid():

            serializer.save()

            return Response(serializer.data)

        else:

            return Response(serializer.errors)

验证

如果我们需要对一些字段进行自定义的验证 DRF也给我们提供了钩子方法 ~

Serializer: 

class BookSerializer(serializers.Serializer):

    id = serializers.IntegerField(read_only=True)

    title = serializers.CharField(max_length=32)

    # 省略了一些字段 跟上面代码里一样的

    # 。。。。。

     def validate_title(self, value):

        if "python" not in value.lower():

            raise serializers.ValidationError("标题必须含有Python")

        return value

view: 

class BookSerializer(serializers.Serializer):

    id = serializers.IntegerField(read_only=True)

    title = serializers.CharField(max_length=32)

    CHOICES = ((1, "Linux"), (2, "Django"), (3, "Python"))

    chapter = serializers.ChoiceField(choices=CHOICES, source="get_chapter_display", read_only=True)

    w_chapter = serializers.IntegerField(write_only=True)

    pub_time = serializers.DateField()

    date_added = serializers.DateField(write_only=True)

    # 新增了一个上架时间字段

    # 省略一些字段。。都是在原基础代码上增加的

    # 。。。。。。

    # 对多个字段进行验证 要求上架日期不能早于出版日期 上架日期要大

    def validate(self, attrs):

        if attrs["pub_time"] > attrs["date_added"]:

            raise serializers.ValidationError("上架日期不能早于出版日期")

        return attrs


def my_validate(value):

    if "敏感词汇" in value.lower:

        raise serializers.ValidationError("包含敏感词汇，请重新提交")

    return value

class BookSerializer(serializers.Serializer):

    id = serializers.IntegerField(read_only=True)

    title = serializers.CharField(max_length=32, validators=[my_validate])

    # 。。。。。。

ModelSerializer

现在我们已经清楚了Serializer的用法，会发现我们所有的序列化跟我们的模型都紧密相关~

那么，DRF也给我们提供了跟模型紧密相关的序列化器ModelSerializer

  • 它会根据模型自动生成一组字段

  • 它简单的默认实现了.update()以及.create()方法

定义一个ModelSerializer序列化器 

class BookSerializer(serializers.ModelSerializer):

    class Meta:

        model = Book

        fields = "__all__"

        # fields = ["id", "title", "pub_time"]

        # exclude = ["user"]

        # 分别是所有字段 包含某些字段 排除某些字段

外键关系的序列化

注意：当序列化类MATE中定义了depth时，这个序列化类中引用字段（外键）则自动变为只读 

class BookSerializer(serializers.ModelSerializer):

    class Meta:

        model = Book

        fields = "__all__"

        # fields = ["id", "title", "pub_time"]

        # exclude = ["user"]

        # 分别是所有字段 包含某些字段 排除某些字段

        depth = 1

# depth 代表找嵌套关系的第几层

自定义字段

我们可以声明一些字段来覆盖默认字段，来进行自定制~

比如我们的选择字段，默认显示的是选择的key，我们要给用户展示的是value。 

class BookSerializer(serializers.ModelSerializer):

    chapter = serializers.CharField(source="get_chapter_display", read_only=True)

    class Meta:

        model = Book

        fields = "__all__"

        # fields = ["id", "title", "pub_time"]

        # exclude = ["user"]

        # 分别是所有字段 包含某些字段 排除某些字段

        depth = 1

Meta中其它关键字参数 

class BookSerializer(serializers.ModelSerializer):

    chapter = serializers.CharField(source="get_chapter_display", read_only=True)

    class Meta:

        model = Book

        fields = "__all__"

        # fields = ["id", "title", "pub_time"]

        # exclude = ["user"]

        # 分别是所有字段 包含某些字段 排除某些字段

        depth = 1

        read_only_fields = ["id"]

        extra_kwargs = {"title": {"validators": [my_validate,]}}

post以及patch请求

由于depth会让我们外键变成只读，所以我们再定义一个序列化的类，其实只要去掉depth就可以了~~ 

class BookSerializer(serializers.ModelSerializer):

    chapter = serializers.CharField(source="get_chapter_display", read_only=True)

    class Meta:

        model = Book

        fields = "__all__"

        # fields = ["id", "title", "pub_time"]

        # exclude = ["user"]

        # 分别是所有字段 包含某些字段 排除某些字段

        read_only_fields = ["id"]

        extra_kwargs = {"title": {"validators": [my_validate,]}}

SerializerMethodField

外键关联的对象有很多字段我们是用不到的 都传给前端会有数据冗余 就需要我们自己去定制序列化外键对象的哪些字段~~ 

class BookSerializer(serializers.ModelSerializer):

    chapter = serializers.CharField(source="get_chapter_display", read_only=True)

    user = serializers.SerializerMethodField()

    publisher = serializers.SerializerMethodField()

    def get_user(self, obj):

        # obj是当前序列化的book对象

        users_query_set = obj.user.all()

        return [{"id": user_obj.pk, "name": user_obj.name} for user_obj in users_query_set]

    def get_publisher(self, obj):

        publisher_obj = obj.publisher

        return {"id": publisher_obj.pk, "title": publisher_obj.title}

    class Meta:

        model = Book

        fields = "__all__"

        # fields = ["id", "title", "pub_time"]

        # exclude = ["user"]

        # 分别是所有字段 包含某些字段 排除某些字段

        read_only_fields = ["id"]

        extra_kwargs = {"title": {"validators": [my_validate,]}}

用ModelSerializer改进上面Serializer的完整版 

class BookSerializer(serializers.ModelSerializer):

    dis_chapter = serializers.SerializerMethodField(read_only=True)

    users = serializers.SerializerMethodField(read_only=True)

    publishers = serializers.SerializerMethodField(read_only=True)

    def get_users(self, obj):

        # obj是当前序列化的book对象

        users_query_set = obj.user.all()

        return [{"id": user_obj.pk, "name": user_obj.name} for user_obj in users_query_set]

    def get_publishers(self, obj):

        publisher_obj = obj.publisher

        return {"id": publisher_obj.pk, "title": publisher_obj.title}

    def get_dis_chapter(self, obj):

        return obj.get_chapter_display()

    class Meta:

        model = Book

        # fields = "__all__"

        # 字段是有序的

        fields = ["id", "title","dis_chapter", "pub_time", "publishers", "users","chapter", "user", "publisher"]

        # exclude = ["user"]

        # 分别是所有字段 包含某些字段 排除某些字段

        read_only_fields = ["id", "dis_chapter", "users", "publishers"]

        extra_kwargs = {"title": {"validators": [my_validate,]}, "user": {"write_only": True}, "publisher": {"write_only": True},

                        "chapter": {"write_only": True}}

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