Include IDs of nested associations in ActiveModel serializers - ruby-on-rails

Question

In some cases nested associations are embedded in the JSON, in others they are not. So far so good, that behaves the way I want. But I want that in the cases where they aren't embedded the IDs of the nested associations are still emitted.
E.g.:
class FooSerializer < ActiveModel::Serializer
attributes :id, :x, :y
belongs_to :bar
end
class BarSerializer < ActiveModel::Serializer
attributes :id, :z
end
When I serialize a Foo object without include: [:bar] I want the result to look like:
{
"id": 123
"x": 1,
"y": 2,
"bar": 456
}
And if bar would be a polymorphic association I'd like something like that:
{
"id": 123
"x": 1,
"y": 2,
"bar": {"id": 456, "schema": "Bar"}
}
Actually I would like the IDs to be strings ("id": "123") because they should be black boxes for the API consumer and definitely not use JavaScript's Number type (which is double precision floating point!).
How do I do that? I didn't find any information about that.

Answer 1

Define attribute id this way in FooSerializer to get it as a string:
attribute :id do
object.to_s
end
"When I serialize a Foo object without include: [:bar] I want the result to look like:"
attribute :bar do
object.bar.id.to_s
end
"And if bar would be a polymorphic association I'd like something like that:"
attribute :bar do
{id: object.barable_id.to_s, schema: object.barable_type}
end
NOTE: I haven't tested this.

Answer 2

I found a way to do that by using a BaseSerializer like this:
class BaseSerializer < ActiveModel::Serializer
attributes :id, :type
def id
if object.id.nil?
nil
else
object.id.to_s
end
end
def type
# I also want all the emitted objects to include a "type" field.
object.class.name
end
def self.belongs_to(key, *args, &block)
attribute key do
assoc = object.class.reflect_on_association(key)
foreign_id = object.send(assoc.foreign_key)
if foreign_id.nil?
nil
elsif assoc.polymorphic?
{
type: object.send(assoc.foreign_type),
id: foreign_id.to_s
}
else
foreign_id.to_s
end
end
super
end
end