sequelize/lib/associations/mixin.js

Sequelize is a promise-based Node.js ORM tool for Postgres, MySQL, MariaDB, SQLite, Microsoft SQL Server, Amazon Redshift and Snowflake’s Data Cloud. It features solid transaction support, relations, eager and lazy loading, read replication and more.

'use strict';

const _ = require('lodash');
const HasOne = require('./has-one');
const HasMany = require('./has-many');
const BelongsToMany = require('./belongs-to-many');
const BelongsTo = require('./belongs-to');

function isModel(model, sequelize) {
  return model
    && model.prototype
    && model.prototype instanceof sequelize.Sequelize.Model;
}

const Mixin = {
  hasMany(target, options = {}) {
    if (!isModel(target, this.sequelize)) {
      throw new Error(`${this.name}.hasMany called with something that's not a subclass of Sequelize.Model`);
    }

    const source = this;

    // Since this is a mixin, we'll need a unique letiable name for hooks (since Model will override our hooks option)
    options.hooks = options.hooks === undefined ? false : Boolean(options.hooks);
    options.useHooks = options.hooks;

    Object.assign(options, _.omit(source.options, ['hooks']));

    if (options.useHooks) {
      this.runHooks('beforeAssociate', { source, target, type: HasMany }, options);
    }

    // the id is in the foreign table or in a connecting table
    const association = new HasMany(source, target, options);
    source.associations[association.associationAccessor] = association;

    association._injectAttributes();
    association.mixin(source.prototype);

    if (options.useHooks) {
      this.runHooks('afterAssociate', { source, target, type: HasMany, association }, options);
    }

    return association;
  },

  belongsToMany(target, options = {}) {
    if (!isModel(target, this.sequelize)) {
      throw new Error(`${this.name}.belongsToMany called with something that's not a subclass of Sequelize.Model`);
    }

    const source = this;

    // Since this is a mixin, we'll need a unique letiable name for hooks (since Model will override our hooks option)
    options.hooks = options.hooks === undefined ? false : Boolean(options.hooks);
    options.useHooks = options.hooks;
    options.timestamps = options.timestamps === undefined ? this.sequelize.options.timestamps : options.timestamps;
    Object.assign(options, _.omit(source.options, ['hooks', 'timestamps', 'scopes', 'defaultScope']));

    if (options.useHooks) {
      this.runHooks('beforeAssociate', { source, target, type: BelongsToMany }, options);
    }
    // the id is in the foreign table or in a connecting table
    const association = new BelongsToMany(source, target, options);
    source.associations[association.associationAccessor] = association;

    association._injectAttributes();
    association.mixin(source.prototype);

    if (options.useHooks) {
      this.runHooks('afterAssociate', { source, target, type: BelongsToMany, association }, options);
    }

    return association;
  },

  getAssociations(target) {
    return Object.values(this.associations).filter(association => association.target.name === target.name);
  },

  getAssociationForAlias(target, alias) {
    // Two associations cannot have the same alias, so we can use find instead of filter
    return this.getAssociations(target).find(association => association.verifyAssociationAlias(alias)) || null;
  }
};

// The logic for hasOne and belongsTo is exactly the same
function singleLinked(Type) {
  return function(target, options = {}) {
    // eslint-disable-next-line no-invalid-this
    const source = this;
    if (!isModel(target, source.sequelize)) {
      throw new Error(`${source.name}.${_.lowerFirst(Type.name)} called with something that's not a subclass of Sequelize.Model`);
    }


    // Since this is a mixin, we'll need a unique letiable name for hooks (since Model will override our hooks option)
    options.hooks = options.hooks === undefined ? false : Boolean(options.hooks);
    options.useHooks = options.hooks;

    if (options.useHooks) {
      source.runHooks('beforeAssociate', { source, target, type: Type }, options);
    }
    // the id is in the foreign table
    const association = new Type(source, target, Object.assign(options, source.options));
    source.associations[association.associationAccessor] = association;

    association._injectAttributes();
    association.mixin(source.prototype);

    if (options.useHooks) {
      source.runHooks('afterAssociate', { source, target, type: Type, association }, options);
    }

    return association;
  };
}

Mixin.hasOne = singleLinked(HasOne);
Mixin.belongsTo = singleLinked(BelongsTo);

module.exports = Mixin;
module.exports.Mixin = Mixin;
module.exports.default = Mixin;