Referencing relation's relations in Django Serializer

Let's say I have some models:

class A(models.Model):
    ...

class B(models.Model):
    my_reference_to_a = models.ForeignKey(A)
    b_field_1 = ...
    b_field_2 = ...

class C(models.Model):
    my_reference_to_b = models.ForeignKey(B)
    c_field_1 = ...
    ...

In my serializer for C, I want to include all of the fields in C, all the fields in B, as well as the reference to A in B (but not the reference to B in C), so the JSON API output would be something like this:

{
    "data": [{
        "type": "C",
        "id": "1",
        "attributes": {
            "b_field_1": "...",
            "b_field_2": "...",
            "c_field_1": "..."
        },
        "relationships": {
            "a": {
                "data": {
                    "type": "A",
                    "id": "1"
                }
            }
        }
    }],
    ...
}

How would I go about this? I've already tried doing something like this inside my serializer for C:

A = ASerializer(source='my_reference_to_b.my_reference_to_a')

But that doesn't work, as DRF doesn't seem to support dotted paths for sources. I've also tried supplying a method that returns the proper model (the model is valid inside the method) as the source, but that outputs the reference in the JSON as:

"a": {
    "data": null
}

On my A model, I also have a reference to another model, D, that is not explicitly stated in A, but is instead defined in D as a OneToMany relationship (Many D models to one A model) with a resource_name on the ForeignKey declared in D, and trying to reference this in C to include that relationship in the JSON doesn't work, either.

Any help would be greatly appreciated.