Using relay-graphql-js with NestJS

While building GraphQL apis, if you need to stay compliant with relay server specifications you can use this relay-graphql library since it provides a bunch of helpers so you can avoid some boilerplate code, specially when dealing with pagination following the connection specifications.

However, you might encounter some problems if you try using this with NestJS GraphQL module since it's heavily focused on object oriented programming paradigms while graphql-relay is more generic and works around composing different functions.

The real problem is how you can specify the given entity connection return type so NestJS can properly work with your schema.

So what we can do is, define a generic function that will return a Connection class that implements Relay's connection interface

import { Type } from "@nestjs/common";
import { Field, ObjectType } from "@nestjs/graphql";
import { Connection as RelayConnection, Edge as RelayEdge, PageInfo as RelayPageInfo } from "graphql-relay";

export function Connection<GraphQLObject>(GenericClass?: Type<GraphQLObject>) {
  @ObjectType({ isAbstract: true })
  abstract class IConnection implements RelayConnection<GraphQLObject> {
    @Field(() => [Edge], { nullable: false })
    edges: Array<RelayEdge<GraphQLObject>>

    @Field(() => PageInfo, { nullable: false })
    pageInfo: PageInfo;
  }

  return IConnection
}

Notice that this class IConnection is implementing RelayConnection that we are importing from "graphql-relay" package.

We are defining that the field edges is of type [Edge]. So let's define it in our function:

@ObjectType({ isAbstract: true })
abstract class Edge<GraphQLObject> implements RelayEdge<GraphQLObject> {
    @Field(() => GenericClass, { nullable: false })
    node: GraphQLObject

    @Field(() => String, { nullable: false })
    cursor: string
}

And the field pageInfo is returning PageInfo, so let's also define it:

@ObjectType({ isAbstract: true })
class PageInfo implements RelayPageInfo {
    @Field(() => String, { nullable: true })
    startCursor: string;

    @Field(() => String, { nullable: true })
    endCursor: string;

    @Field(() => Boolean, { nullable: false })
    hasPreviousPage: boolean;

    @Field(() => Boolean, { nullable: false })
    hasNextPage: boolean;
}

Your function Connection should look like this now:

export function Connection<GraphQLObject>(GenericClass?: Type<GraphQLObject>) {
    @ObjectType({ isAbstract: true })
    class PageInfo implements RelayPageInfo {
        @Field(() => String, { nullable: true })
        startCursor: string;

        @Field(() => String, { nullable: true })
        endCursor: string;

        @Field(() => Boolean, { nullable: false })
        hasPreviousPage: boolean;

        @Field(() => Boolean, { nullable: false })
        hasNextPage: boolean;
    }

    @ObjectType({ isAbstract: true })
    abstract class Edge<GraphQLObject> implements RelayEdge<GraphQLObject> {
        @Field(() => GenericClass, { nullable: false })
        node: GraphQLObject

        @Field(() => String, { nullable: false })
        cursor: string
    }

    @ObjectType({ isAbstract: true })
    abstract class IConnection implements RelayConnection<GraphQLObject> {
        @Field(() => [Edge], { nullable: false })
        edges: Array<RelayEdge<GraphQLObject>>

        @Field(() => PageInfo, { nullable: false })
        pageInfo: PageInfo;
    }

    return IConnection
}

You might be wondering, why not simply use generic and separated classes. Unfortunately typescript has some limitations that won't make this generic classes work as we would like. (You can read a bit more about it here).

Now, the only thing you would need to do, for each of your project's entities, anytime you need to implement pagination following the connection specficiations, is this:

You could create a user.connection.ts and define it like this:

import { ObjectType } from "@nestjs/graphql";
import {Connection} from "../../_types/models/connection.model";
import { User } from "./user.model";

@ObjectType()
export class UserConnection extends Connection<User>(User) {
}

And in your resolver you'll be able to do something like this:

import { connectionFromPromisedArray } from "graphql-relay";

/**
* ... rest of your code ...
*/

@Query(() => FinancialRecordConnection)
async users(@Args({ type: () => ConnectionArguments }) args: ConnectionArguments) {
	return connectionFromPromisedArray(this.usersService?.list(), args)
}

Note:

In your function Connection if you get an error like this:

Return type of exported function has or is using private name 'IConnection'.ts(4060)

You have two options:

1. Go to your tsconfig.json file and set false to declarations property.
2. Explicitly type the return of the Connection function with any.