Improvements for flat_one

[aaronrosenthal]

First let me say I love the idea of flat_one. But I think it has an issue that I'd like to see improved.

It's pretty common that an association can be null in the schema, and simply using flat_one will result in errors when trying to serialize the attributes of the association. Since we have conditionality it's easily resolved with:

flat_one :blob, serializer: BlobSerializer, if: -> { object.blob }

but from my experience so far there's never a case where I wouldn't add conditionality. I think there's a few improvements that could fix this:

Solution 1

Make the conditionality implicit for flat associations. By this I mean the library should not even attempt to serialize the values for nil associations, similar to how one_if works. This would eliminate the need to ever make flat_one explicitly conditional.

Solution 2

Similar to above, but instead of implicit conditionality just serialize null values for all the attributes in flat_one's serializer. One advantage of this solution is it allows flexibility in whether the entire serialization should be conditional or if it should return null values in the JSON.

Solution 3

Allow passing a block to flat_one for additional flexibility. For example:

flat_one :blob, serializer: BlobSerializer do
  object.blob || BlobSerializer.new
end

as one way to workaround nil references. This could also be useful for serializing stored JSON in the schema (which could be nullable) with serializers that use hash_attributes. Contrived example below:

class NameSerializer < Oj::Serializer
  hash_attributes :first_name, :last_name
end

class UserSerializer < Oj::Serializer
  identifier

  flat_one :name_json, serializer: NameSerializer do
    object.name_json || {}
  end
end