Custom serializer for BuiltMap

[andreavaccari]

Hi @davidmorgan, I have a User entity defined with built_value and including a BuiltMap. I use StandardJsonSerializer to produce objects I persist to Firestore. I'd like to specify a custom serializer for the BuiltMap field so that it's serialized to an object with shape { ids: [...], entities: {...} }.

The reasons for this are: 1) we need to maintain insertion order and Firestore reorders map keys alphabetically; 2) we can't simply serialize the map to a list because some Firestore lookups only work on maps. This pattern is common enough that Redux offers a standardized solution.

Could you give me a hint on the best way to accomplish this? Thank you!

[davidmorgan]

This is a built_value question rather than a built_collection question :) so please re-open over there if you still have questions.

You could replace the existing BuiltMap serializer with a fully custom one, i.e. write a replacement for the built-in BuiltMapSerializer. This only works if you want all BuiltMap fields to work like that.

Otherwise, I'm afraid there isn't a way to set a different serializer per field--it's always based on type. I think you'd need to create your own type which is basically a copy of BuiltMap but comes with its own serializer.