ModelSerializer use knowledge _serializers.SerializerMethodField () usage scenario summary

serializers.SerializerMethodField hook and combined methods may be implemented for some fields like ModelSerializer secondary processing returns, as follows: 
1, based on the processing to ModelSerializer foreign key data

model as follows:

A、Project

class Project(models.Model):
    """
    项目表
    """
    id = models.AutoField(primary_key=True)
    name = models.CharField(max_length=50, verbose_name='项目名称')
    version = models.CharField(max_length=50, verbose_name='版本')
    description = models.CharField(max_length=1024, blank=True, null=True, verbose_name='描述')
    status = models.BooleanField(default=True, verbose_name='状态')
    LastUpdateTime = models.DateTimeField(auto_now=True, verbose_name='最近修改时间')
    createTime = models.DateTimeField(auto_now_add=True, verbose_name='创建时间')
    user = models.ForeignKey(User, on_delete=models.SET_NULL, null=True, max_length=1024, verbose_name='创建人')

    def __unicode__(self):
        return self.name

    def __str__(self):
        return self.name

    class Meta:
        verbose_name = '项目'
        verbose_name_plural = '项目'

B, ApiInfo (foreign key to project)

class ApiInfo(models.Model):
    """
    接口信息
    """
    id = models.AutoField(primary_key=True)
    project = models.ForeignKey(Project, related_name='api_project', on_delete=models.CASCADE, verbose_name='所属项目')

    def __unicode__(self):
        return self.name

    def __str__(self):
        return self.name

    class Meta:
        verbose_name = '接口'
        verbose_name_plural = '接口管理'

2, project the ModelSerializer follows:

class ProjectSerializer(serializers.ModelSerializer):
    """
    项目信息序列化
    """
    apiCount = serializers.SerializerMethodField()
    LastUpdateTime = serializers.DateTimeField(format="%Y-%m-%d %H:%M:%S", required=False, read_only=True)
    createTime = serializers.DateTimeField(format="%Y-%m-%d %H:%M:%S", required=False, read_only=True)
    user = serializers.CharField(source='user.first_name')

    class Meta:
        model = Project
        fields = ('id', 'name', 'version', 'type', 'status', 'LastUpdateTime', 'createTime', 'apiCount',
                  'dynamicCount', 'memberCount', 'description', 'user')

    def get_apiCount(self, obj):
        return obj.api_project.all().count()

  
通过 obj.以它为外键的类字段的related_name 取出以它为外键的对象，该对象可以进行进行一般的model类操作（如obj.api_project.all().count()、obj.api_project.get（XXX查询条件）.XXX属性），从而处理以它为外键的数据