Supercharge Your Schemas with
Custom Directives
Ryan Chenkie
-
JavaScript Consultant
@ryanchenkie
-
Google Developer Expert
-
angularcasts.io
Consumer or Creator?
What is a
Schema Directive?
"Directives provide a way to describe alternate runtime execution and type validation behavior in a GraphQL document."
– GraphQL Spec 2.12 (June 2018 release)
Built-In Directives
"GraphQL implementations should provide the @skip and @include directives."
– GraphQL Spec 3.13 (June 2018 release)
(queries)
Built-In Directives
"GraphQL implementations that support the type system definition language must provide the @deprecated directive if representing deprecated portions of the schema."
– GraphQL Spec 3.13 (June 2018 release)
(schemas)
What do schema directives look like?
foo: String
@myDirective
(myArg: "Bar")
What kinds of problems can we solve with schema directives?
Anything that requires a change to behavior at runtime
- Internationalization
- Authentication and access control
- String formatting
- Caching
- Async work such as REST API calls
Implementing custom schema directives used to suck
youtu.be/4_Bcw7BULC8
Now it's easy with Apollo
Let's visit the schema
SchemaDirectiveVisitor
visitFieldDefinition
visitObject
visitSchema
visitScalar
visitArgumentDefinition
visitInterface
visitUnion
visitEnum
visitEnumValue
visitInputObject
visitInputFieldDefinition
What is the directive named?
What arguments does it take?
Where does it work?
Target field definitions
Get the argument passed in
Resolve the field with "something different"
Register the schema directive
Put the directive on any fields desired
Directives can be async
Using context for authorization
Schema directives aren't the only option
Middleware is another option
npm install graphql-middleware
There's an emerging preference for code-first schemas
bit.ly/schema-first
Problems with Schema First
- Schemas and resolvers must be kept in sync
- Modularizing schemas
- Redundancy in schemas
- Developer experience
- Composing distributed schemas
Lots of tooling needed to get around these problems
Code-first server development can offer benefits
Slides
bit.ly/custom-schema-directives
Thank You!
@ryanchenkie
Supercharge Your Schemas with Custom Directives
By Ryan Chenkie
Supercharge Your Schemas with Custom Directives
GraphQL's schema language is beautiful. It allows us to author data models concisely and communicate with teammates clearly. Using Apollo, we can also write directives to supercharge our schemas with custom behavior. Let's talk about how to write custom directives and the benefits they offer.
