fix(belongs-to-many): correctly throw error when no 'as' is defined for self N:M

lib/associations/belongs-to-many.js

@@ -61,6 +61,10 @@ var BelongsToMany = function(source, target, options) {
   this.doubleLinked = false;
   this.as = this.options.as;
 
+  if (!this.as && this.isSelfAssociation) {
+    throw new Error('\'as\' must be defined for many-to-many self-associations');
+  }
+
   if (this.as) {
     this.isAliased = true;
 
@@ -87,10 +91,6 @@ var BelongsToMany = function(source, target, options) {
    * If self association, this is the target association - Unless we find a pairing association
    */
   if (this.isSelfAssociation) {
-    if (!this.as) {
-      throw new Error('\'as\' must be defined for many-to-many self-associations');
-    }
-
     this.targetAssociation = this;
   }
 

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

@@ -117,10 +117,12 @@ describe(Support.getTestDialectTeaser('belongsToMany'), function() {
         , Invite = current.define('invite', {});
 
       User.Followers = User.belongsToMany(User, {
-        through: UserFollowers
+        as: 'Followers',
+        through: UserFollowers,
       });
 
       User.Invites = User.belongsToMany(User, {
+        as: 'Invites',
         foreignKey: 'InviteeId',
         through: Invite
       });
@@ -131,6 +133,29 @@ describe(Support.getTestDialectTeaser('belongsToMany'), function() {
       expect(User.Followers.otherKey).not.to.equal(User.Invites.foreignKey);
     });
 
+    it('correctly generates a foreign/other key when none are defined', function () {
+      var User = current.define('user', {})
+        , UserFollowers = current.define('userFollowers', {
+            id: {
+              type: DataTypes.INTEGER,
+              primaryKey: true,
+              autoIncrement: true
+            }
+          }, {
+            timestamps: false
+          });
+
+      User.Followers = User.belongsToMany(User, {
+        as: 'Followers',
+        through: UserFollowers
+      });
+
+      expect(User.Followers.foreignKey).to.be.ok;
+      expect(User.Followers.otherKey).to.be.ok;
+
+      expect(Object.keys(UserFollowers.rawAttributes).length).to.equal(3);
+    });
+
     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', {})