Django REST framework serializers are defined as classes that inherit from rest_framework.serializers.Serializer. For example, given a dataabse model Book:

class Book(models.Model):
    title = models.CharField(max_length=50, verbose_name='Title')
    pub_date = models.DateField(verbose_name='Publication Date', null=True)
    reads = models.IntegerField(default=0, verbose_name='Read Count')
    comments = models.IntegerField(default=0, verbose_name='Comment Count')
    cover = models.ImageField(upload_to='covers', verbose_name='Cover Image', null=True)

We can create a corresponding serializer:

class BookSerializer(serializers.Serializer):
    """Book data serializer"""
    id = serializers.IntegerField(label='ID', read_only=True)
    title = serializers.CharField(label='Title', max_length=50)
    pub_date = serializers.DateField(label='Publication Date', required=False)
    reads = serializers.IntegerField(label='Read Count', required=False)
    comments = serializers.IntegerField(label='Comment Count', required=False)
    cover = serializers.ImageField(label='Cover Image', required=False)

Field Types and Options

Common field types include:

• BooleanField, CharField, EmailField
• IntegerField, FloatField, DecimalField
• DateTimeField, DateField, TimeField
• FileField, ImageField
• ListField, DictField

Field options include:

• max_length, min_length
• allow_blank, trim_whitespace
• max_value, min_value
• read_only, write_only
• required, default

Creating Serializer Objects

Serializer constructor:

Serializer(instance=None, data=empty, **kwargs)

Example usage:

book = Book.objects.get(id=1)
serializer = BookSerializer(book)
serializer.data

For querysets:

books = Book.objects.all()
serializer = BookSerializer(books, many=True)
serializer.data

Related Object Nesting

Several approaches for handling related objects:

1. PrimaryKeyRelatedField:

publisher = serializers.PrimaryKeyRelatedField(queryset=Publisher.objects.all())

2. StringRelatedField:

publisher = serializers.StringRelatedField()

3. Nested serializers:

publisher = PublisherSerializer()

Deserialization and Validation

Validation methods:

1. Field-level validation:

def validate_title(self, value):
    if 'django' not in value.lower():
        raise serializers.ValidationError("Book must be about Django")
    return value

2. Object-level validatino:

def validate(self, data):
    if data['reads'] < data['comments']:
        raise serializers.ValidationError("Read count cannot be less than comments")
    return data

3. Validators:

def about_django(value):
    if 'django' not in value.lower():
        raise serializers.ValidationError("Book must be about Django")

class BookSerializer(serializers.Serializer):
    title = serializers.CharField(validators=[about_django])

ModelSerializer

Automaticlaly generates serializers from models:

class BookSerializer(serializers.ModelSerializer):
    class Meta:
        model = Book
        fields = '__all__'

Customization options:

class BookSerializer(serializers.ModelSerializer):
    class Meta:
        model = Book
        fields = ('id', 'title', 'pub_date')
        read_only_fields = ('id',)
        extra_kwargs = {
            'reads': {'min_value': 0},
            'comments': {'min_value': 0}
        }