GraphQL & Sequelize: Users and followers/following - sql

Question

I'm attempting to set up my User GraphQL model to have followers and following attributes to query on. However I'm having trouble setting up the relationship in Sequelize. I'm trying to use a Follower model as a Join Table and setup a BelongsToMany association, but haven't been able to get it working. Can anyone suggest what to do or point out what I'm doing wrong?
I've come up with a temporary solution by manually querying, which you can see in my User.model.ts, but I believe there is a better way to do it using proper configuration.
I'm using typescript wrappers around GraphQL and Sequelize, TypeGraphQL and sequelize-typescript respectively, as well as PostgreSQL.
User.model.ts
// VENDOR
import { ObjectType, Field, ID } from 'type-graphql';
import { Model, Table, Column, PrimaryKey, Unique, IsUUID, HasMany, DefaultScope, AllowNull, DataType, BelongsToMany } from 'sequelize-typescript';
// APP
import Post from '../post/post.types';
import Follower from '../follower/follower.types';
/** User model for GraphQL & Database */
#Table({ timestamps: false, tableName: 'users' }) // tell sequelize to treat class as table model
#DefaultScope(() => ({ include: [{ model: Post.scope(), as: 'posts' }] })) // tell sequelize to include posts in its default queries
#ObjectType() // tell GraphQL to treat class as GraphQL model
export default class User extends Model<User>{
#PrimaryKey
#Unique
#AllowNull(false)
#IsUUID(4)
#Column(DataType.UUID)
#Field(() => ID)
id: string;
#Unique
#AllowNull(false)
#Column
#Field()
ci_username: string;
#AllowNull(false)
#Column
#Field()
username: string;
#AllowNull(false)
#Column
#Field()
first_name: string;
#Column
#Field()
last_name: string;
#Column
#Field({ nullable: true })
profile_picture?: string;
// #BelongsToMany(() => User, { otherKey: 'user_id', as: 'followers', through: () => Follower })
// #Field(() => [User])
// followers: User[];
// MY TEMPORARY SOLUTION USING MANUAL QUERYING
#Field(() => [User])
get followers(): Promise<User[]> {
return Follower.findAll({ where: { user_id: this.id } })
.then(records => records.map(record => record.follower_id))
.then((follower_ids: string[]) => {
return User.findAll({ where: { id: follower_ids }});
})
}
// DOES NOT WORK, BUT I BELIEVE COULD POTENTIALLY LEAD TO BETTER SOLUTION
#BelongsToMany(() => User, { otherKey: 'follower_id', as: 'following', through: () => Follower })
#Field(() => [User])
following: User[];
#HasMany(() => Post)
#Field(() => [Post])
posts: Post[];
}
Follower.model.ts
// VENDOR
import { Model, Table, Column, PrimaryKey, Unique, IsUUID, AllowNull, DataType, Index, ForeignKey, AutoIncrement } from 'sequelize-typescript';
// APP
import User from '../user/user.types';
/** Follower model for Database */
#Table({ timestamps: false, tableName: 'followers' }) // tell sequelize to treat class as table model
export default class Follower extends Model<Follower>{
#PrimaryKey
#AutoIncrement
#Unique
#AllowNull(false)
#Column
id: number;
#AllowNull(false)
#IsUUID(4)
#Index
#ForeignKey(() => User)
#Column(DataType.UUID)
user_id: string;
#AllowNull(false)
#IsUUID(4)
#Index
#ForeignKey(() => User)
#Column(DataType.UUID)
follower_id: string;
}
GraphQL Query
{
users: allUsers {
id
username
first_name
last_name
following {
username
id
}
}
}
GraphQL Response / Error
{
"errors": [
{
"message": "Cannot return null for non-nullable field User.following.",
"locations": [
{
"line": 7,
"column": 5
}
],
"path": [
"users",
0,
"following"
],
"extensions": {
"code": "INTERNAL_SERVER_ERROR",
"exception": {
"stacktrace": [
"Error: Cannot return null for non-nullable field User.following.",
" at completeValue (/Users/jsainz237/Projects/trueview/trueview-api/node_modules/graphql/execution/execute.js:560:13)",
" at /Users/jsainz237/Projects/trueview/trueview-api/node_modules/graphql/execution/execute.js:492:16"
]
}
}
}
],
"data": null
}
Any help is appreciated.

Answer 1

You need to write a #FieldResolver manually that will resolve the relation and return proper data.
Another solution is to rely on ORM capabilities and lazy relations - when the returned base entity contains a promise as a field, so when .then() is called, it automatically fetches the relation for the database.