AttributeError at /api/module/list/

Question

I want many to many fields to be displayed in module serializer instead of id, these are my serializers

class TrainerSerializer(serializers.ModelSerializer):

    class Meta:
        model = User
        fields = ['id', ]


class ModuleSerializer(serializers.ModelSerializer):

    trainer = serializers.CharField(source='trainer.username')

    class Meta:
        model = Module
        fields = ['id', 'title', 'duration', 'trainer', 

'publish_choice']

class Trainer(models.Model):
    user = models.ForeignKey(User, on_delete=models.SET_NULL, null=True)

    def __str__(self):
        return str(self.user)

    class Meta:
        ordering = ['pk']


class Module(models.Model):
    title = models.CharField(max_length=80, unique=True)
    duration = models.IntegerField(verbose_name='Duration in Days/ Weeks', blank=True, null=True)
    trainer = models.ManyToManyField(Trainer, blank=True)
    detail = models.TextField(verbose_name='Program Details', blank=True, null=True)
    notify = models.BooleanField(default=False)
    publish_choice = models.CharField(verbose_name='Publish/ Draft',
                                      max_length=80, choices=PUBLISH_CHOICES, default='publish')

and this is the error message

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

Sumithran · Accepted Answer · 2020-12-07 04:52:48Z

1

We have a depth parameter in the serializer MetaClass. we can make use of it like below. depth=1 will retrieve all fields of a relation.

class ModuleSerializer(serializers.ModelSerializer):

     class Meta:
        model = Module
        fields = ['id', 'title', 'duration', 'trainer', 'publish_choice']
        depth = 1

for reference DRF-Documentation on serializers

answered Dec 7, 2020 at 4:52

Sumithran

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2 Comments

Sumithran Over a year ago

@Biju consider accepting this answer if it worked for you.

Ngoc Pham Over a year ago

Carefull with depth. If your model have more fk or many to many, depth will query all of this.

Ngoc Pham · Accepted Answer · 2020-12-07 06:47:21Z

0

Its raise exception because serializers.CharField(source='trainer.username') not match ManyRelatedManager in model trainer = models.ManyToManyField(Trainer, blank=True).

If you want get all username instead of id, you can try add Custom type serialzier like this:

class ModuleSerializer(serializers.ModelSerializer):
     trainer = serializers.SerializerMethodField()

     def get_trainer(self, obj):
        results = []
        for item in obj.trainers.all():
            results.append(item.username)
        return results

     class Meta:
        model = Module
        fields = ['id', 'title', 'duration', 'trainer', 'publish_choice']

trainer will return array of username relation with Module

edited Dec 7, 2020 at 6:47

answered Dec 7, 2020 at 4:43

Ngoc Pham

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2 Comments

Biju Over a year ago

this throw the error "'Module' object has no attribute 'users'"

Ngoc Pham Over a year ago

ah sr, i edited my answer. can you try again?

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