A unions is an abstract type made up of multiple possible concrete types.

No common fields are declared in a union. Compare to Absinthe.Type.Interface.

Because it’s necessary for the union to determine the concrete type of a resolved object, you must either:

• Provide a :resolve_type function on the union
• Provide a :is_type_of function on each possible concrete type

union :search_result do
  description "A search result"

  types [:person, :business]
  resolve_type fn
    %Person{}, _ -> :person
    %Business{}, _ -> :business
  end
end

• :name - The name of the union type. Should be a TitleCased binary. Set automatically.
• :description - A nice description for introspection.
• :types - The list of possible types.
• :resolve_type - A function used to determine the concrete type of a resolved object. See also Absinthe.Type.Object’s :is_type_of. Either resolve_type is specified in the union type, or every object type in the union must specify is_type_of

The :resolve_type function will be passed two arguments; the object whose type needs to be identified, and the Absinthe.Execution struct providing the full execution context.

The :__reference__ key is for internal use.