unhashable type: 'OrderedDict'

Question

I am encountering an issue in Django when I try to do a PUT request in Postman.

I suspect the issue is because I have nested serializers in my model class, but I am not sure.

class Foo(models.Model):
    foo_name = models.CharField(max_length=50, unique=True)

    foo_statistics = models.ManyToManyField(TrainStatistics)

class FooSerializer(serializers.ModelSerializer):
    blah_statistics = BlahStatisticsSerializer(many=True)

    class Meta:
        model = Foo
        fields = ('foo_statistics')
        depth = 2 

    def create(self, validated_data):
        """
        Create and return a new `Summary` instance, given the validated data.
        """

        blah_statistics_data = validated_data.pop('blah_statistics')
        foo = Foo(**validated_data)

        for blah_statistic in blah_statistics_data:
            FooStatistic.objects.create(summary=summary, **train_statistic)
        return summary

    def update(self, instance, validated_data):
        """
        Update and return an existing `Foo` instance, given the validated data.
        """
        instance.blah_statistics = validated_data.get('blah_statistics', instance.blah_statistics) # This line is causing problems

Any idea what could be causing this issue?

Answer 1

The problem is that the validated data turns train_statistics into a OrderedDict(always it's a bit tricky working with nested serializers), so OrderedDicts are unhashable, so when you try to ".get" it raises an error.

An option is to set your field train_statistics into read only.

Then in your update() method, instead of using validated_data to get train_statistics, use request.data for getting them. Do the same for create() method.

class SummarySerializer(serializers.ModelSerializer):
    train_statistics = TrainStatisticsSerializer(many=True, read_only=True)

    class Meta:
        model = Summary
        fields = ('train_statistics')
        depth = 2 

    def create(self, validated_data):
        """
        Create and return a new `Summary` instance, given the validated data.
        """
        request = self.context['request']
        train_statistics_data = request.data.get('train_statistics')
        summary = Summary.objects.create(**validated_data)

        for train_statistic in train_statistics_data:
            TrainStatistics.objects.create(summary=summary, **train_statistic)
        return summary

    def update(self, instance, validated_data):
        """
        Update and return an existing `Summary` instance, given the validated data.
        """
        request = self.context['request']
        instance.train_statistics =request.data.get('train_statistics', instance.train_statistics) # This line is causing problems

When you call your serializer, you need to pass request object as context data.

SummarySerializer(instance, data=data, context={'request':request})

or

SummarySerializer(data=data, context={'request':request})