fix(belongs-to-many): properly pair association based on the through argument

The code would previously pair association based on the through.model argument of the original options.
However options.through.model would generally be undefined since users usually just pass through: Model and the normalization to through.model
actually happened on association.through rather than options.through.
Normalization now happens on the options set before being assigned to association.through

lib/associations/belongs-to-many.js

@@ -36,11 +36,23 @@ var Utils = require('./../utils')
 var BelongsToMany = function(source, target, options) {
   Association.call(this);
 
+  options = options || {};
+
+  if (options.through === undefined || options.through === true || options.through === null) {
+    throw new Error('belongsToMany must be given a through option, either a string or a model');
+  }
+
+  if (!options.through.model) {
+    options.through = {
+      model: options.through
+    };
+  }
+
   this.associationType = 'BelongsToMany';
   this.source = source;
   this.target = target;
   this.targetAssociation = null;
-  this.options = options || {};
+  this.options = options;
   this.sequelize = source.modelManager.sequelize;
   this.through = options.through;
   this.scope = options.scope;
@@ -71,16 +83,6 @@ var BelongsToMany = function(source, target, options) {
     this.isSelfAssociation ? (this.as || this.target.tableName) : this.target.tableName
   );
 
-  if (this.through === undefined || this.through === true || this.through === null) {
-    throw new Error('belongsToMany must be given a through option, either a string or a model');
-  }
-
-  if (!this.through.model) {
-    this.through = {
-      model: this.through
-    };
-  }
-
   /*
    * If self association, this is the target association - Unless we find a pairing association
    */

test/unit/associations/belongs-to-many.test.js

@@ -11,7 +11,7 @@ var chai = require('chai')
   , Promise   = current.Promise;
 
 describe(Support.getTestDialectTeaser('belongsToMany'), function() {
-   describe('optimizations using bulk create, destroy and update', function() {
+  describe('optimizations using bulk create, destroy and update', function() {
     var User = current.define('User', { username: DataTypes.STRING })
       , Task = current.define('Task', { title: DataTypes.STRING })
       , UserTasks = current.define('UserTasks', {});
@@ -63,27 +63,47 @@ describe(Support.getTestDialectTeaser('belongsToMany'), function() {
         expect(this.destroy).to.have.been.calledOnce;
       });
     });
+  });
 
-    describe('belongsToMany', function () {
-      it('works with singular and plural name for self-associations', function () {
-        // Models taken from https://github.com/sequelize/sequelize/issues/3796
-        var Service = current.define('service', {})
-          , Instance = Service.Instance;
+  describe('self-associations', function () {
+    it('does not pair multiple self associations with different through arguments', function () {
+      var User = current.define('user', {})
+        , UserFollowers = current.define('userFollowers', {})
+        , Invite = current.define('invite', {});
 
-        Service.belongsToMany(Service, {through: 'Supplements', as: 'supplements'});
-        Service.belongsToMany(Service, {through: 'Supplements', as: {singular: 'supplemented', plural: 'supplemented'}});
+      User.Followers = User.belongsToMany(User, {
+        through: UserFollowers
+      });
 
-        expect(Instance.prototype).to.have.property('getSupplements').which.is.a.function;
+      User.Invites = User.belongsToMany(User, {
+        foreignKey: 'InviteeId',
+        through: Invite
+      });
 
-        expect(Instance.prototype).to.have.property('addSupplement').which.is.a.function;
-        expect(Instance.prototype).to.have.property('addSupplements').which.is.a.function;
+      expect(User.Followers.paired).not.to.be.ok;
+      expect(User.Invites.paired).not.to.be.ok;
 
-        expect(Instance.prototype).to.have.property('getSupplemented').which.is.a.function;
-        expect(Instance.prototype).not.to.have.property('getSupplementeds').which.is.a.function;
+      expect(User.Followers.otherKey).not.to.equal(User.Invites.foreignKey);
+    });
 
-        expect(Instance.prototype).to.have.property('addSupplemented').which.is.a.function;
-        expect(Instance.prototype).not.to.have.property('addSupplementeds').which.is.a.function;
-      });
+    it('works with singular and plural name for self-associations', function () {
+      // Models taken from https://github.com/sequelize/sequelize/issues/3796
+      var Service = current.define('service', {})
+        , Instance = Service.Instance;
+
+      Service.belongsToMany(Service, {through: 'Supplements', as: 'supplements'});
+      Service.belongsToMany(Service, {through: 'Supplements', as: {singular: 'supplemented', plural: 'supplemented'}});
+
+      expect(Instance.prototype).to.have.property('getSupplements').which.is.a.function;
+
+      expect(Instance.prototype).to.have.property('addSupplement').which.is.a.function;
+      expect(Instance.prototype).to.have.property('addSupplements').which.is.a.function;
+
+      expect(Instance.prototype).to.have.property('getSupplemented').which.is.a.function;
+      expect(Instance.prototype).not.to.have.property('getSupplementeds').which.is.a.function;
+
+      expect(Instance.prototype).to.have.property('addSupplemented').which.is.a.function;
+      expect(Instance.prototype).not.to.have.property('addSupplementeds').which.is.a.function;
     });
   });
 });