Django Rest Framework Many=False producing errors

Question

I am stuck on trying to solve an issue with the Serializers and related fields using the django-rest-framework. Currently I have a model that looks like this:

class DataSetModel(models.Model):
    title = models.CharField(max_length=200)
    description = models.TextField()

class DataPointModel(models.Model):
    dataSet = models.ForeignKey(DataSetModel, related_name='dataPoints')
    label = models.CharField(max_length=200)

My serializers look like this:

class DataPointSerializer(serializers.ModelSerializer):
    class Meta:
        model = DataPointModel
        fields = ('pk','label')

class DataSetSerializer(serializers.ModelSerializer):
    dataPoints = DataPointSerializer(many=True, read_only=True)

    class Meta:
        model = DataSetModel
        fields = ('pk','title')

The problem I am having is when I try to change the "many=False" in the serializer produces this error:

Got AttributeError when attempting to get a value for field label on serializer DataPointSerializer. The serializer field might be named incorrectly and not match any attribute or key on the RelatedManager instance. Original exception text was: 'RelatedManager' object has no attribute 'label'.

Since this is only ever one model object (one-to-many relationship), I want to get the result as a single object vs a list of one object.

Am I doing this the right way? I thought that turning the "many=False" it would fetch the first record in an nested query.

Any insight would be greatly appreciated.

levi · Accepted Answer · 2015-03-13 06:37:19Z

1

You can't set many=False, because dataPoints is a related field that returns a queryset containing a list of instances, not just an instance.

When you do DataPointModel.dataPoints that returns a queryset, it can't returns just an instance. So setting many=False, it wouldn't get the first element of the list.

edited Mar 13, 2015 at 6:37

answered Mar 13, 2015 at 6:31

levi

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3 Comments

renderbox Over a year ago

Levi, thanks for the answer. How would you suggest handling this in my Model set-up?

levi Over a year ago

@renderbox why is your point? what do you want to do ? render just one instance model ?

renderbox Over a year ago

I am nesting the serialized model so it's just one call to the server. The point is to not have to go through extra processing on the client end (of processing a list) and having it be delivered ready to be consumed.

renderbox · Accepted Answer · 2015-03-13 23:10:45Z

1

So the solve I came to was refactoring my models with where the Foreign Keys are attached.

Here is the fix I implemented:

class DataSetModel(models.Model):
    title = models.CharField(max_length=200)
    description = models.TextField()
    dataPoint = models.ForeignKey(DataPointModel)

class DataPointModel(models.Model):
    label = models.CharField(max_length=200)

Moving it to the DataSetModel automatically joins the data model if you set 'many=False' in the Serializer object.

answered Mar 13, 2015 at 23:10

renderbox

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Comments

Chetan Thambad · Accepted Answer · 2021-08-24 12:24:27Z

1

Write your DataPointModel as below. It should work then

class DataPointModel(models.Model):
    dataSet = models.OneToOneField(DataSetModel, related_name='dataPoints')
    label = models.CharField(max_length=200)

answered Aug 24, 2021 at 12:24

Chetan Thambad

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