AWS AppSync - Implement many to many connections using 1-M #connections and a joining #model - database

Question

Following AWS documentation (https://aws-amplify.github.io/docs/cli-toolchain/graphql > Many-To-Many Connections), I try to understand the workaround example they provide for many to many connections (which seems not supported yet by Amplify).
The schema is:
type Post #model {
id: ID!
title: String!
editors: [PostEditor] #connection(name: "PostEditors")
}
# Create a join model and disable queries as you don't need them
# and can query through Post.editors and User.posts
type PostEditor #model(queries: null) {
id: ID!
post: Post! #connection(name: "PostEditors")
editor: User! #connection(name: "UserEditors")
}
type User #model {
id: ID!
username: String!
posts: [PostEditor] #connection(name: "UserEditors")
}
Using AWS AppSync Console, so far I'm able to:
Create a user using this mutation:
mutation {
createUser(input:{
username: "theUserName"
}){
username
}
}
Create a post using this mutation:
mutation {
createPost(input: {
title: "second post"
}){
title
}
}
But I don't understand how to add multiple editors to a post? So far, I'm able to add editors to a post using PostEditor join, but in their example, there is this statement (which I don't understand very well), so I don't think this is the good approach:
# Create a join model and disable queries as you don't need them
# and can query through Post.editors and User.posts
So I guess that using this join model to perform mutation is not what I have to do. Nevertheless, to be able to create this relation between a post and an editor, I created a mutation (retrieving "postEditorPostId" and "postEditorEditorId" from both previous mutations):
mutation {
createPostEditor(input:{
postEditorPostId: "XXX-XXX-XXX"
postEditorEditorId: "YYY-YYY-YYY"
}){
post {
title
}
editor {
username
posts {
items {
post {
title
}
}
}
}
}
}
Do I need to perform this previous mutation everytime I add a new editor (so the mutation will remain the same but "postEditorEditorId" will change? it seems obviously not a scalable approach, if for example the UI allows an admin to add 50 or more new editors (so it will need 50 mutations).
Finally I can get the information I need using this query:
query{
getUser(id: "YYY-YYY-YYY"){
username
posts {
items {
post {
title
}
}
}
}
}
Is there a better way (I suppose) to add editors to a post?
edit:
Using a promise, I am able to add multiple editors to a post, but it involves to execute as mutation as mutations as there are users:
const users = [{id: "U1", username: "user1"}, {id: "U2", username: "user2"}];
const post = { id: "P1", title: "Post 1" };
/*
After creating two users and a post using the approriate mutations
Using the CreatePost join below to make user1 and user2 editor on Post 1
*/
function graphqlCreatePostEditor(editorID) {
return new Promise((resolve, reject) => {
resolve(
API.graphql(graphqlOperation(createPostEditor, {
input: {
postID: post.id,
}
}))
)
})
}
let promises = users.map(user=> {
return graphqlCreatePostEditor(user.id)
.then(e => {
console.log(e)
return e;
})
});
Promise.all(promises)
.then(results => {
console.log(results)
})
.catch(e => {
console.error(e);
})
Still looking if there is a way to pass an array in a sigle mutation.

Answer 1

For simplicity sake, I'm lets go with a User model and a Project model where a user can have many projects and belong to many projects.
Note: The creation of join table as I've described it here is for the Amplify JS API for React / React Native / JavaScript
User model
type User #model {
id: ID!
username: String!
projects: [UserProject] #connection(name: "UserProject")
}
Project model
type Project #model {
id: ID!
project_title: String!
users: [UserProject] #connection(name: "ProjectUser")
}
Join table
type UserProject #model {
id: ID!
user: User #connection(name: "UserProject")
project: Project #connection(name: "ProjectUser")
}
Creation of Join table
Prerequisite: Fetch both user.id and project.id however you want to do that.
const UserProjectDetails = {
userProjectUserId: user.id
userProjectProjectId: project.id
};
API.graphql({ query: mutations.createUserProject, variables: {input: UserProjectDetails}})
And there you have it.
This article on dev.to was also pretty straight to the point:
https://dev.to/norrischebl/modeling-relationships-join-table-graphql-aws-amplify-appsync-1n5f