Directives

Directives provide a way to describe additional options to the GraphQL executor.

Directives is a GraphQL term; in practice, directives are much like meta data in Clojure, or annotations in Java.

Directives allow Lacinia to change the incoming query based on additional criteria. For example, we can use directives to include or skip a field if certain criteria are met.

Currently Lacinia supports just the two standard query directives: @skip and @include, but future versions may include more.

Warning

Directive support is currently in transition towards some support for custom directives.

Directives in Schema IDL

When using GraphQL SDL Parsing, the directive keyword allows new directives to be defined. Directive definitions can be defined for executable elements (such as a field selection in a query document), or for type system elements (such as an object or field definition in the schema).

Directives may also be defined in an EDN schema; the root :directive-defs element is a map of directives types to directive definition. A directive defintion defines the types of any arguments, as well as a set of locations.

{:directive-defs
 {:access
  {:locations #{:field-definition}
   :args {:role {:type (non-null String)}}}}

 :queries
 {:ultimate_answer
  {:type String
   :directives [{:directive-type :access
                 :directive-args {:role "deep-thought"}}]}}}

This defines a field definition directive, @access, and applies it to the ultimate_answer query field.

Directive Validation

Directives are validated:

  • Directives may have arguments, and the argument types must be rooted in known scalar types.
  • Directives may be placed on schema elements (objects and input objects, unions, enums and enum values, fields, etc.). Directives placed on an element are verified to be applicable to the location.

Warning

Directive support is evolving quickly; full support for directives, including argument type validation, is forthcoming, as is an API to identify schema and executable directives.

The goal of the current stage is to support parsing of SDL schemas that include directive definitions and directives on elements.

Introspection hasn’t caught up to to these changes; custom directives are not identified, nor are directives on elements.

@deprecated directive

The @deprecated directive is supported. This enables Deprecation of object fields and enum values.