Lambda Fields - Graphql

Documentation
1

Schema

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

For example, to define a lambda function for the rank and bio fields in Author:

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

You can also define @lambda fields on interfaces:

interface Character {
        id: ID!
        name: String! @search(by: [exact])
        bio: String @lambda
}
type Human implements Character {
        totalCredits: Float
}
type Droid implements Character {
        primaryFunction: String
}

Resolvers

Once the schema is ready, you can define your JavaScript mutation 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 JavaScript lambda functions for

  • Author,
  • Character,
  • Human, and
  • Droid

and add them as resolvers:

const authorBio = ({parent: {name, dob}}) => `My name is ${name} and I was born on ${dob}.`
const characterBio = ({parent: {name}}) => `My name is ${name}.`
const humanBio = ({parent: {name, totalCredits}}) => `My name is ${name}. I have ${totalCredits} credits.`
const droidBio = ({parent: {name, primaryFunction}}) => `My name is ${name}. My primary function is ${primaryFunction}.`
self.addGraphQLResolvers({
    "Author.bio": authorBio,
    "Character.bio": characterBio,
    "Human.bio": humanBio,
    "Droid.bio": droidBio
})

Another example, adding a resolver for rank using a graphql call:

async function rank({parents}) {
    const idRepList = parents.map(function (parent) {
        return {id: parent.id, rep: parent.reputation}
    });
    const idRepMap = {};
    idRepList.sort((a, b) => a.rep > b.rep ? -1 : 1)
        .forEach((a, i) => idRepMap[a.id] = i + 1)
    return parents.map(p => idRepMap[p.id])
}
self.addMultiParentGraphQLResolvers({
    "Author.rank": rank
})

Example

If you execute this lambda query

query {
	queryAuthor {
		name
		bio
		rank
	}
}

You should see a response such as

{
	"queryAuthor": [
		{
			"name":"Ann Author",
			"bio":"My name is Ann Author and I was born on 2000-01-01T00:00:00Z.",
			"rank":3
		}
	]
}

In the same way, if you execute this lambda query on the Character interface

query {
	queryCharacter {
		name
		bio
	}
}

You should see a response such as

{
	"queryCharacter": [
		{
			"name":"Han",
			"bio":"My name is Han."
		},
		{
			"name":"R2-D2",
			"bio":"My name is R2-D2."
		}
	]
}

Note that the Human and Droid types will inherit the bio lambda field from the Character interface.

For example, if you execute a queryHuman query with a selection set containing bio, then the lambda function registered for Human.bio will be executed:

query {
  queryHuman {
    name
    bio
  }
}

Response:

{
  "queryHuman": [
    {
      "name": "Han",
      "bio": "My name is Han. I have 10 credits."
    }
  ]
}
This is a companion discussion topic for the original entry at https://dgraph.io/docs/graphql/lambda/field/