Reverse Relationships?

[neighlyd]

Hello,

I may be missing something, so I apologize if I am, but I am unable to get DRF-Flex-Fields to work properly with a reverse relationships . Is this not something that drf-flex-fields can do or am I messing up somehow?

[rsinger86]

Hi there, this should work with reverse relationships. You'd just need to make sure that the "source" arg matches what you've configured via the related= arg on your model FK.

Would help me debug if you could post some code of your model and serializer.

[neighlyd]

Hi,

Thanks for the response. I apologize for not posting code before.

It seems that the issue may not actually be related to reverse relationships as I had previously thought. Following your response, I was able to get them working using the related= argument (or, alternatively, the <model>_set notation).

It appears that the real issue I was having was actually an order of operations one. Since my reverse relation serializer is defined below the serializer in which I want to expand the set, I can't reach it (either it is undefined at runtime, or if I use quotations as per normal DRF reference, it spits an error). An example may help.

serializers.py
class ArchiveSerializer(FlexFieldsModelSerializer):
    class Meta:
        model = models.Archive
        name = 'archive'
        fields = ('id', 'name', 'website', 'notes')

    expandable_fields = {
        'record_set': (RecordSerializer, {'source': 'record_set', 'many': True})
    }

class RecordSerializer(FlexFieldsModelSerializer):
    class Meta:
        model = models.Record
        fields = ('id', 'name', 'record_type', 'reel', 'notes', 'archive')

    expandable_fields = {
        'archive': (ArchiveSerializer, {'source': 'archive'})
    }

This throws an error when the server is run, because RecordSerializer is undefined.

If I put RecordSerializer in quotes within ArchiveSerializer like so:

class ArchiveSerializer(FlexFieldsModelSerializer):
    class Meta:
        model = models.Archive
        name = 'archive'
        fields = ('id', 'name', 'website', 'notes')

    expandable_fields = {
        'record_set': ('RecordSerializer', {'source': 'record_set', 'many': True})
    }

The error goes away and the server runs. However, when I navigate to ArchiveSerializer I receive the following error:

list index out of range

It looks like it's getting tripped up on line 77 of DRF-Flex-Field's serializers.py.

Obviously, having a circular expansion would be no good, but since children often expand their parents and parents often have need to expand a set of their children I'm finding the need to reference circularly (though not expanding circularly). Is the only alternative to have two versions of RecordSerializer?

[rsinger86]

Ah, so this is something I need to document. If you want to lazily evaluate the reference to your nested serializer class from a string inside expandable_feilds, you need to use this syntax:

expandable_fields = {
    'record_set': ('<app_name>.RecordSerializer', {'source': 'record_set', 'many': True})
}

Substitute the name of your Django app where the serializer is found for <app_name>. But if the serializer exists in the same app that it is called from, I really should allow the syntax that you used... Similar to how Django evaluates references to model FKs. I'll look to update this in a future version. Thanks for raising this issue.

[neighlyd]

Oh great! Thanks so much for the information. I will go ahead and refactor my code to that instead of having a bunch of extra serializers.

I appreciate it!!

[willcroft]

+1 for this info in the docs! Ran into the same issue by wanting to keep my serializers in alphabetical order. Thanks so much!