Define a Custom Resolver

Create a New Custom Resolver

In the App Services UI, click GraphQL in the navigation sidebar and then select the Custom Resolvers tab.

Click the Add a Custom Resolver button to open the configuration screen for a new custom resolver.

Define the Resolver Field Name

Specify App Servicese name for the resolver in the GraphQL Field Name input. App Services exposes the custom resolver in its parent type using this name, so the name should describe what the resolver does in a way that is useful to developers who work with the GraphQL API.

Define the Parent Type

App Services exposes every custom resolver as a field on a parent type. The parent type can be a root-level query, mutation, or a generated document type.

In the Parent Type dropdown, select one of the following options:

type Query {
  myCustomQuery: DefaultPayload
  ...
}

type Mutation {
  myCustomMutation: DefaultPayload
  ...
}

type Task {
  myCustomTaskProperty: DefaultPayload
  ...
}

Define the Input Type

A custom resolver can accept input parameters from the incoming query or mutation. You can use an existing generated input type or define a new custom input type specifically for the resolver.

If you specify an input type, App Services exposes the input parameter in the custom resolver's generated GraphQL schema definition as an optional parameter that accepts the specified input type. If you don't specify an input type, the custom resolver does not accept any arguments.

In the Input Type dropdown, select one of the following options:

Option	Description
None	The resolver does not accept any input. Example A custom resolver named myCustomQuery that does not accept an input has the following generated schema: type Query { myCustomQuery: DefaultPayload ... }
Scalar	The resolver uses an existing scalar type from the generated GraphQL schema. In the second dropdown input, select either a single scalar or an array of multiple scalars of the same type. Example A custom resolver named myCustomQuery that uses the Scalar Type option to specify an input type of DateTiem has the following generated schema: type Query { myCustomQuery(input: DateTime): DefaultPayload ... }
Existing Type	The resolver uses an existing input type from the generated GraphQL schema. In the second dropdown input, select either a single input object or an array of multiple input objects of the same type. Example A custom resolver named myCustomQuery that uses the Existing Type option to specify an input type of TaskInsertInput has the following generated schema: type Query { myCustomQuery(input: TaskInsertInput): DefaultPayload ... }
Custom Type	App Services generates a new input type specifically for the resolver based on a schema that you define. The schema must be an object that contains at least one property and a title field that defines a unique name for the generated input type. Example A custom resolver named myCustomQuery that uses the Custom Type option with an input type named MyCustomQueryInput has the following generated schema: input MyCustomQueryInput { someArgument: String; } type Query { myCustomQuery(input: MyCustomQueryInput): DefaultPayload ... }

Define the Payload Type

All GraphQL resolvers must return a payload that conforms to a specific type in the schema. For a custom resolver, you can use an existing generated document type, define a new custom payload type specifically for the resolver, or use a default payload. App Services includes the specified payload type in the custom resolver's generated GraphQL schema definition.

In the Payload Type dropdown, select one of the following options:

Option	Description
DefaultPayload	The resolver returns the automatically generated DefaultPayload type which has the following signature: type DefaultPayload { status: String! } The status field will always resolve to "complete" regardless of the resolver function's return value. { status: "complete" } Example A custom resolver named myCustomQuery that uses the DefaultPayload option has the following generated schema: type Query { myCustomQuery: DefaultPayload ... }
Scalar	The resolver uses an existing scalar type from the generated GraphQL schema. In the second dropdown input, select either a single scalar or an array of multiple scalars of the same type. Example A custom resolver named myCustomQuery that uses the Scalar Type option to specify a payload type of DateTime has the following generated schema: type Query { myCustomQuery: DateTime ... }
Existing Type	The resolver returns an existing document type from the generated GraphQL schema. In the second dropdown input, select either a single document type or an array of multiple documents of the same type. Example A custom resolver named myCustomQuery that uses the Existing Type option to specify an input type of TaskInsertInput has the following generated schema: A custom resolver named myCustomQuery that uses the Existing Type option to specify a payload type of [Task] has the following generated schema: type Query { myCustomQuery: [Task] ... }
Custom Type	App Services generates a new payload type specifically for the resolver based on a schema that you define. The schema must be an object that contains at least one property and a title field that defines a unique name for the generated input type. Example A custom resolver named myCustomQuery that uses the Custom Type option with a payload type named MyCustomQueryPayload has the following generated schema: input MyCustomQueryPayload { someValue: String; } type Query { myCustomQuery: MyCustomQueryPayload ... }

Define the Resolver Function

When a user calls a custom resolver App Services executes the resolver function and returns the result, which must conform to the resolver's Payload Type.

App Services passes the function any input data from the operation, if applicable. If the resolver is a computed property on a document type, App Services passes the function the specific document that the resolver was called on.

A custom resolver function has one of two possible signatures, depending on whether or not it accepts an input:

exports = function myCustomResolver(input, source) {
  // The `input` parameter that contains any input data provided to the resolver.
  // The type and shape of this object matches the resolver's input type.
  const { someArgument } = input;
  // If the resolver is a computed property, `source` is the parent document.
  // Otherwise `source` is undefined.
  const { _id, name } = source;
  // The return value must conform to the resolver's configured payload type
  return {
    "someValue": "abc123",
  };
}

exports = function myCustomResolver(source) {
  // If the resolver is a computed property, `source` is the parent document.
  // Otherwise `source` is undefined.
  const { _id, name } = parent;
  // The return value must conform to the resolver's configured payload type
  return {
    "someValue": "abc123",
  };
}

To define the resolver function, click the Function dropdown and either select an existing function or create a new one.

Save and Deploy the Resolver

Once you have configured the resolver, click Save and deploy your application. Once deployed, you can call the custom resolver through the GraphQL API.