Django rest fetch data from bridge model - django

Question

I want to get all the user details and list of all the roles against the
user details model
My Models
class UserDetail(models.Model):
user = models.OneToOneField(User, on_delete=models.CASCADE,
related_name='userdetail_user', default='111')
cn = models.CharField(max_length=200)
sn = models.CharField(max_length=200)
u_id = models.CharField(max_length=200)
display_name_cn = models.CharField(max_length=200)
display_name_en = models.CharField(max_length=200)
given_name = models.CharField(max_length=200)
employee_number = models.CharField(max_length=200)
email = models.CharField(max_length=200)
created_at = models.DateTimeField(default=datetime.now, blank=True)
last_login = models.DateTimeField(default=datetime.now, blank=True)
def __str__(self):
return self.given_name
class Role(models.Model):
title = models.CharField(max_length=20)
description = models.CharField(max_length=200)
created_at = models.DateTimeField(default=datetime.now, blank=True)
last_updated = models.DateTimeField(default=datetime.now, blank=True)
status = models.BooleanField(default=True)
def __str__(self):
return self.title
class UserRole(models.Model):
userdetail = models.ForeignKey(UserDetail, on_delete=models.CASCADE,
related_name='userrole_userdetail')
role = models.ForeignKey(Role, on_delete=models.CASCADE)
approver = models.ForeignKey(UserDetail, on_delete=models.SET_NULL,
null=True,
related_name='userrole_userdetail_approver')
created_at = models.DateTimeField(default=datetime.now, blank=True)
last_updated = models.DateTimeField(default=datetime.now, blank=True)
status = models.BooleanField(default=True)
My Serializers
class UserSerializer(serializers.ModelSerializer):
class Meta:
model = User
fields = ('id', 'username', 'email')
class UserRoleSerializer(serializers.ModelSerializer):
class Meta:
model = UserRole
fields = (
'id', 'userdetail', 'role', 'approver', 'last_updated', 'status')
depth = 1
def to_representation(self, instance):
representation = super(UserRoleSerializer, self).to_representation(
instance)
representation['userdetail'] = UserDetailSerializer(
instance.userdetail).data
representation['role'] = RoleSerializer(instance.role).data
representation['approver'] = UserDetailSerializer(
instance.approver).data
return representation
class RoleSerializer(serializers.ModelSerializer):
class Meta:
model = Role
fields = ('id', 'title', 'description', 'last_updated', 'status')
class UserDetailSerializer(serializers.ModelSerializer):
user = UserSerializer()
roles = serializers.SerializerMethodField(read_only=True)
class Meta:
model = UserDetail
fields = ('id', 'roles', 'user', 'cn', 'sn', 'u_id', 'display_name_cn',
'display_name_en', 'given_name', 'employee_number', 'email',
'last_login')
lookup_field = 'u_id'
def get_roles(self, obj):
roles = UserRole.objects.filter(userdetail=obj)
return roles
When I try to fetch all the user details it gives me an error
"Object of type 'UserRole' is not JSON serializable".
I have already tried to serialize the list of object fetched inside get_roles method of UserDetailsSerializer but its no help

Answer 1

In your Serializers, you have to replace
roles = serializers.SerializerMethodField(read_only=True)
With
userrole_userdetail = UserRoleSerializer(many=True, read_only=True)
Its because your FK relation name must match the related name given in the model. Also in UserRoleSerializer you do not need the to_representation method.