audiobookshelf/server/models/CollectionBook.js

const { DataTypes, Model } = require('sequelize')

class CollectionBook extends Model {
  constructor(values, options) {
    super(values, options)

    /** @type {UUIDV4} */
    this.id
    /** @type {number} */
    this.order
    /** @type {UUIDV4} */
    this.bookId
    /** @type {UUIDV4} */
    this.collectionId
    /** @type {Date} */
    this.createdAt
  }

  static removeByIds(collectionId, bookId) {
    return this.destroy({
      where: {
        bookId,
        collectionId
      }
    })
  }

  static init(sequelize) {
    super.init({
      id: {
        type: DataTypes.UUID,
        defaultValue: DataTypes.UUIDV4,
        primaryKey: true
      },
      order: DataTypes.INTEGER
    }, {
      sequelize,
      timestamps: true,
      updatedAt: false,
      modelName: 'collectionBook'
    })

    // Super Many-to-Many
    // ref: https://sequelize.org/docs/v6/advanced-association-concepts/advanced-many-to-many/#the-best-of-both-worlds-the-super-many-to-many-relationship
    const { book, collection } = sequelize.models
    book.belongsToMany(collection, { through: CollectionBook })
    collection.belongsToMany(book, { through: CollectionBook })

    book.hasMany(CollectionBook, {
      onDelete: 'CASCADE'
    })
    CollectionBook.belongsTo(book)

    collection.hasMany(CollectionBook, {
      onDelete: 'CASCADE'
    })
    CollectionBook.belongsTo(collection)
  }
}

module.exports = CollectionBook