GraphQL How to properly implement chain resolvers? - graphql

Question

One of the main concepts of GraphQL is being able to select the data we're interested in, while omitting the unnecessary fields. To achieve that we can use resolvers. Each such is responsible for providing data for a particular type.
I've created a small example to present my problem.
The error it returns is:
"Cannot return null for non-nullable field Parent.child."
I could just let the Parent create the whole object, but then where's the benefit of resolving delegation, what would be the point of creating the Child resolver and then the whole GraphQL concept of resolver chains?
How to make the parent call the Child resolver to resolve its child field?
const { ApolloServer, gql } = require('apollo-server');
const typeDefs = gql`
type Child {
name: String!
}
type Parent {
name: String!
child: Child!
}
type Query {
getParent: Parent!
}
`;
(async function () {
const server = new ApolloServer({
typeDefs,
resolvers: {
Query: {
getParent: () => {
return {
name: "parent",
};
},
},
Child: {
name: () => "child",
},
}
});
await server.listen();
})();

Answer 1

Here is how you should write your resolver:
import { gql,ApolloServer } from "apollo-server";
const typeDefs = gql`
type Child {
name: String!
}
type Parent {
name: String!
child: Child!
}
type Query {
getParent: Parent!
}
`;
(async function () {
const server = new ApolloServer({
typeDefs,
resolvers: {
Query: {
getParent: () => {
return {
name: "parent",
};
},
},
Parent: {
child: () => {
return {
name: "child",
}
}
},
}
});
await server.listen().then(({url}) => {
console.log(url)
});
})();
I'm also a beginner in gql, but I will give my thoughts.
When you define a new ObjectType:Parent, you should write the ObjectField Resolver for it if you have nested ObjectType, which means you should write the resolver specific the Object and its child's resolver function. that way , the nested object could found the way to fetch the data.
The Query and Mutation is just two special entry point.
refer to this: https://graphql.org/learn/schema/#the-query-and-mutation-types