Pass correct initial_data to ListSerializer child (#5345)

[daggaz]

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Description

refs #5345

Thought I'd have a bash at this too.

I left setting initial_data when we iterate over child.to_representation(...). In theory you might want access to it there too, because you could be doing an "update":

Serializer(data=[...], instance=[...]).data

But I guess there's nothing to stop those list being different lengths or in different orders so mapping from one to the other isn't really sensible. I figured this is fine since ListSerializer doesn't support update() out of the box anyway.

[carltongibson]

I'm inclined to say no to this. I think it adds a chunk of noise for a marginal use-case.

I'd prefer to see this added to a project-level ListSerializer subclass rather than added to DRF itself.

@encode/django-rest-framework-core-team Anyone got a view on this?

[carltongibson]

@daggaz Whilst I do see the point of it, I'm going to say no to this as an addition to the core framework. For me the benefit doesn't seem worth the extra complexity.

If you were to were to wrap this up as a third party package we could happily link to this from the docs. Users could then customise their list serialiser class. I think that's the best option.

Thanks for the input!