Lambda Queries - Graphql

Documentation
1

Schema

To set up a lambda query, first you need to define it on your GraphQL schema by using the @lambda directive.

For example, to define a lambda query for Author that finds out authors given an author’s name:

type Author {
    id: ID!
    name: String! @search(by: [hash, trigram])
    dob: DateTime
    reputation: Float
}
type Query {
    authorsByName(name: String!): [Author] @lambda
}

Resolver

Once the schema is ready, you can define your JavaScript query function and add it as resolver in your JS source code. To add the resolver you can use either the addGraphQLResolvers or addMultiParentGraphQLResolvers methods.

For example, to define the JavaScript authorsByName() lambda function and add it as resolver:

async function authorsByName({args, dql}) {
    const results = await dql.query(`query queryAuthor($name: string) {
        queryAuthor(func: type(Author)) @filter(eq(Author.name, $name)) {
            name: Author.name
            dob: Author.dob
            reputation: Author.reputation
        }
    }`, {"$name": args.name})
    return results.data.queryAuthor
}
self.addGraphQLResolvers({
    "Query.authorsByName": authorsByName,
})

Example

Finally, if you execute this lambda query

query {
	authorsByName(name: "Ann Author") {
		name
		dob
		reputation
	}
}

You should see a response such as

{
	"authorsByName": [
		{
			"name":"Ann Author",
			"dob":"2000-01-01T00:00:00Z",
			"reputation":6.6
		}
	]
}
This is a companion discussion topic for the original entry at https://dgraph.io/docs/graphql/lambda/query/