Type Errors

The GraphQL specification requires certain assumptions to hold true when executing a query. However, it’s possible that some code would violate that assumption, resulting in a type error.

Here are two type errors that you can customize in GraphQL-Ruby:

• A field with null: false returned nil

• A field returned a value as a union or interface, but that value couldn’t be resolved to a member of that union or interface.

You can specify behavior in these cases by defining a Schema.type_error hook:

class MySchema < GraphQL::Schema
  def self.type_error(err, query_ctx)
    # Handle a failed runtime type coercion
  end
end

It is called with an instance of GraphQL::UnresolvedTypeError or GraphQL::InvalidNullError and the query context (a GraphQL::Query::Context).

If you don’t specify a hook, you get the default behavior:

• Unexpected nils add an error the response’s "errors" key

• Unresolved Union / Interface types raise GraphQL::UnresolvedTypeError

An object that fails type resolution is treated as nil.