linux-kernel-module-cheat/rootfs_overlay/lkmc/nodejs/sequelize/association_many_to_many.js

#!/usr/bin/env node

// https://stackoverflow.com/questions/22958683/how-to-implement-many-to-many-association-in-sequelize/67973948#67973948

const assert = require('assert');
const path = require('path');

const { Sequelize, DataTypes } = require('sequelize');

const sequelize = new Sequelize({
  dialect: 'sqlite',
  storage: 'tmp.' + path.basename(__filename) + '.sqlite',
});

(async () => {

// Create the tables.
const User = sequelize.define('User', {
  name: { type: DataTypes.STRING },
}, {});
const Post = sequelize.define('Post', {
  body: { type: DataTypes.STRING },
}, {});
// UserLikesPost is the name of the relation table.
// Sequelize creates it automatically for us.
// On SQLite that table looks like this:
// CREATE TABLE `UserLikesPost` (
//   `createdAt` DATETIME NOT NULL,
//   `updatedAt` DATETIME NOT NULL,
//   `UserId` INTEGER NOT NULL REFERENCES `Users` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
//   `PostId` INTEGER NOT NULL REFERENCES `Posts` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
//   PRIMARY KEY (`UserId`, `PostId`)
// );
User.belongsToMany(Post, {through: 'UserLikesPost'});
Post.belongsToMany(User, {through: 'UserLikesPost'});
await sequelize.sync({force: true});

// Create some users and likes.

const user0 = await User.create({name: 'user0'})
const user1 = await User.create({name: 'user1'})
const user2 = await User.create({name: 'user2'})

const post0 = await Post.create({body: 'post0'});
const post1 = await Post.create({body: 'post1'});
const post2 = await Post.create({body: 'post2'});

// Autogenerated add* methods

// Make user0 like post0
await user0.addPost(post0)
// Also works.
//await user0.addPost(post0.id)
// Make user0 and user2 like post1
await post1.addUsers([user0, user2])

// Autogenerated get* methods

// Get likes by a user.

const user0Likes = await user0.getPosts({order: [['body', 'ASC']]})
assert(user0Likes[0].body === 'post0');
assert(user0Likes[1].body === 'post1');
assert(user0Likes.length === 2);

const user1Likes = await user1.getPosts({order: [['body', 'ASC']]})
assert(user1Likes.length === 0);

const user2Likes = await user2.getPosts({order: [['body', 'ASC']]})
assert(user2Likes[0].body === 'post1');
assert(user2Likes.length === 1);

// Same as get but with the user ID instead of the model object.
{
  const user0Likes = await Post.findAll({
    include: [{
      model: User,
      where: {id: user0.id},
    }],
    order: [['body', 'ASC']],
  })
  assert(user0Likes[0].body === 'post0');
  assert(user0Likes[1].body === 'post1');
  assert(user0Likes.length === 2);
}

// Yet another way that can be more useful in nested includes.
{
  const user0Likes = (await User.findOne({
    where: {id: user0.id},
    include: [{
      model: Post,
    }],
    order: [[Post, 'body', 'ASC']],
  })).Posts
  assert(user0Likes[0].body === 'post0');
  assert(user0Likes[1].body === 'post1');
  assert(user0Likes.length === 2);
}

// Get users that liked a given likes.

const post0Likers = await post0.getUsers({order: [['name', 'ASC']]})
assert(post0Likers[0].name === 'user0');
assert(post0Likers.length === 1);

const post1Likers = await post1.getUsers({order: [['name', 'ASC']]})
assert(post1Likers[0].name === 'user0');
assert(post1Likers[1].name === 'user2');
assert(post1Likers.length === 2);

const post2Likers = await post2.getUsers({order: [['name', 'ASC']]})
assert(post2Likers.length === 0);

// Autogenerated has* methods

// Check if user likes post.
assert( await user0.hasPost(post0))
assert( await user0.hasPost(post0.id)) // same
assert( await user0.hasPost(post1))
assert(!await user0.hasPost(post2))

// Check if post is liked by user.
assert( await post0.hasUser(user0))
assert(!await post0.hasUser(user1))
assert(!await post0.hasUser(user2))

// AND of multiple has checks at once.
assert( await user0.hasPosts([post0, post1]))
assert(!await user0.hasPosts([post0, post1, post2]))

// Autogenerated count* methods
assert(await user0.countPosts() === 2)
assert(await post0.countUsers() === 1)

// Autogenerated remove* methods

// user0 doesn't like post0 anymore.
await user0.removePost(post0)
// user0 and user 2 don't like post1 anymore.
await post1.removeUsers([user0, user2])
// Check that no-one likes anything anymore.
assert(await user0.countPosts() === 0)
assert(await post0.countUsers() === 0)

// Autogenerated create* method
// Create a new post and automatically make user0 like it.
const post3 = await user0.createPost({'body': 'post3'})
assert(await user0.hasPost(post3))
assert(await post3.hasUser(user0))

// Autogenerated set* method
// Make user0 like exactly these posts. Unlike anything else.
await user0.setPosts([post1, post2])
assert(!await user0.hasPost(post0))
assert( await user0.hasPost(post1))
assert( await user0.hasPost(post2))
assert(!await user0.hasPost(post3))

await sequelize.close();
})();