local-resolver.md

@localResolver Directive

General

@localResolver lets you create a stub resolver, but make no mistake - this can be used with full parameter injection syntax to create complex resolvers.

The optional mergeStrategy parameter allows choosing between replacing/merging/deep merging with the existing resolver value for the field. The Replace strategy is used by default.

Full parameters:

enum LocalResolverMergeStrategy {
    Replace
    Merge
    MergeDeep
}

directive @localResolver(
    value: JSON!
    mergeStrategy: LocalResolverMergeStrategy = Replace
    enabledIf: Boolean = "{ true }"
)

Arguments

• value: (object, optional, default `null) - object or string that may be evaluated using Argument injection mechanism. This value will be returned instead of resolver execution or will be merged with it.
• mergeStrategy: (enum, optional, default Replace) - defines if the resolver won't be executed or its execution result will be merged with the value.
• enabledIf: (string, optional, default true) string that is evaluated using Argument injection mechanism. If its value is false the directive will execute the resolver and return its result.

Examples

Example of replacing the existing resolver value:

type Query {
  isAlive: Boolean @localResolver(value: true)
  jsonEcho(input: JSON!): JSON @localResolver(value: { wrapper: "{args.input}" })
}

type User {
  firstName: String!
  lastName: String!
  fullName: String! @localResolver(value: "{source.firstName} {source.lastName}")
}

Example of merging with the existing resolver value:

type User {
    firstName: String!
    lastName: String!
    fullName: String // not supplied by the resolver
}

type Query {
    getUser: User! @localResolver(value: { fullName: "${source.firstName} ${source.lastName}" }, mergeStrategy: Merge)
}

The optional enabledIf parameter allows ignore the value if its content is evaluated to false. For example:

type Foo {
  bar: String! @localResolver(enabledIf: "{!source.bar}", value: "N/A")
}

In this case if the source object doesn't have bar property or it's null or undefined the field value will be "N/A". Otherwise it will be the result of the original field resolver. When the mergeStrategy is set to Merge or MergeDeep the original resolver result and the value parameter evaluation will be merged only if the enabledIf is true. Otherwise the field value will be the result of the original field resolver.

Flow Diagram