How to get specific fields from child serializers? - django

Question

Say, there are two models:
class Model1(models.Model):
r = models.CharField(max_length=200)
class Model2(models.Model):
p = models.CharField(max_length=200)
m = models.ForeignKey(Model1,on_delete=models.CASCADE)
The serializers are :
class Model1Serializer(serializers.Serializer):
class Meta:
model = Model1
fields = '__all__'
class Model2Serializer(serializers.Serializer):
class Meta:
model = Model2
fields = '__all__'
The given Model1 serializer returns the output as:
{
"id": 1,
"r": "r_value"
}
and model 2 serializer output is:
{
"id":1,
"p: "p_value",
"m": 1
}
The thing is that I also want the r value in the model2 serializer output. How to do that?

Answer 1

You need to specify new field with correct source - you can read more in docs.
Option 1: With class Serializer:
class Model2Serializer(serializers.Serializer):
id = serializers.IntegerField()
p = serializers.CharField()
r = serializers.CharField(source='m.r')
class Meta:
model = Model2
fields = '__all__'
Output: {'p': u'pppp', 'r': u'rrrrr', 'id': 1}
Option 2: With class ModelSerializer:
class Model2Serializer(serializers.ModelSerializer):
r = serializers.CharField(source='m.r')
class Meta:
model = Model2
fields = '__all__'
Output: {'p': u'pppp', 'r': u'rrrrr', 'm': 1L, u'id': 1}
Option 3: To include whole Model1:
class Model1Serializer(serializers.ModelSerializer):
class Meta:
model = Model1
fields = '__all__'
class Model2Serializer(serializers.Serializer):
m = Model1Serializer()
class Meta:
model = Model2
fields = '__all__'
Output: {'m': OrderedDict([(u'id', 1), ('r', u'rrrrr')])}

Answer 2

1. If you want r as attrs of m
define Serializer class of specific Relational Field
class Model2Serializer(serializers.ModelSerializer):
m = Model1Serializer()
class Meta:
model = Model2
fields = '__all__'
output:
[
{
"id": 1,
"m": {
"id": 1,
"r": "RED"
},
"p": "Light RED"
},
{
"id": 2,
"m": {
"id": 1,
"r": "RED"
},
"p": "Dark RED"
}
]
2. If you want just r Using ReadOnlyField
You can use ReadOnlyField
class Model2Serializer(serializers.ModelSerializer):
r = serializers.ReadOnlyField(source='m.r')
class Meta:
model = Model2
fields = '__all__'
output:
[
{
"id": 1,
"r": "RED",
"p": "Light RED",
"m": 1
},
{
"id": 2,
"r": "RED",
"p": "Dark RED",
"m": 1
}
]
3. If you want just r Using SerializerMethodField()
You can you SerializerMethodField and ist read only as well
class Model2Serializer(serializers.ModelSerializer):
r = serializers.SerializerMethodField()
class Meta:
model = Model2
fields = '__all__'
def get_r(self, instance):
return instance.m.r
output:
[
{
"id": 1,
"r": "RED",
"p": "Light RED",
"m": 1
},
{
"id": 2,
"r": "RED",
"p": "Dark RED",
"m": 1
}
]

Answer 3

Try this
class Model1Serializer(serializers.Serializer):
class Meta:
model = Model1
fields = '__all__'
class Model2Serializer(serializers.Serializer):
r = Model1Serializer(many=True, source="model1_set")
class Meta:
model = Model2
fields = '__all__'

Answer 4

DRF makes it quite easy if you already have a Model1Serializer for Model1:
class Model2Serializer(serializers.Serializer):
m = Model1Serializer()
class Meta:
model = Model2
fields = '__all__'
That should be it.

Answer 5

Simply use depth=1 in your serializer Meta. Like this:
class Model2Serializer(serializers.Serializer):
class Meta:
model = Model2
fields = '__all__'
depth = 1
This will go for a level of 1 into the Foreign keys that do exist in that model. (By the way, I don't recommend it for big models. But it's perfectly suitable for your situation)