Lambda Fields

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
  isMe: Boolean @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 a resolver in your JS source code. To add the resolver you can use either the addGraphQLResolvers or addMultiParentGraphQLResolvers methods.

Note A Lambda Field resolver can use a combination of parents, parent, dql, or graphql inside the function.

Tip This example uses parent for the resolver function. You can find additional resolver examples using dql in the Lambda queries article, and using graphql in the Lambda mutations article.

For example, to define JavaScript lambda functions for…

Author,
Character,
Human, and
Droid

…and add them as resolvers, do the following:

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,
});

An 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,
});

An example of using the client provided JWT to return true if the custom claim for USER from the JWT matches the Author’s id.

async function isMe({ parent, authHeader }) {
  if (!authHeader) return false;
  if (!authHeader.value) return false;
  const headerValue = authHeader.value;
  if (headerValue === "") return false;
  const base64Url = headerValue.split(".")[1];
  const base64 = base64Url.replace(/-/g, "+").replace(/_/g, "/");
  const allClaims = JSON.parse(atob(base64));
  if (!allClaims["https://my.app.io/jwt/claims"]) return false;
  const customClaims = allClaims["https://my.app.io/jwt/claims"];
  return customClaims.USER === parent.id;
}

self.addGraphQlResolvers({
  "Author.isMe": isMe,
});

Example

If you execute this lambda query

query {
  queryAuthor {
    name
    bio
    rank
    isMe
  }
}

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,
      "isMe": false
    }
  ]
}

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."
    }
  ]
}