Fix so that belongsToMany association keys aren't deleted (#5871)

fix(belongs-to-many): constraint cascading are now properly preserved 

changelog.md

 # Future
 - [FIXED] Postgres DECIMAL precision. (PostgreSQL) [#4893](https://github.com/sequelize/sequelize/issues/4893)
 - [FIXED] removeColumn tries to delete non-existant foreign key constraint (mysql) [#5808](https://github.com/sequelize/sequelize/issues/5808)
+- [FIXED] Relation constraints not being applied correctly [#5865](https://github.com/sequelize/sequelize/issues/5865)
 
 # 3.23.0
 - [FIXED] Invalid query generated when using LIKE + ANY [#5736](https://github.com/sequelize/sequelize/issues/5736)

lib/associations/belongs-to-many.js

@@ -311,9 +311,17 @@ BelongsToMany.prototype.injectAttributes = function() {
   this.foreignIdentifier = this.otherKey;
 
   // remove any PKs previously defined by sequelize
+  // but ignore any keys that are part of this association (#5865)
   _.each(this.through.model.rawAttributes, function(attribute, attributeName) {
     if (attribute.primaryKey === true && attribute._autoGenerated === true) {
-      delete self.through.model.rawAttributes[attributeName];
+      if (attributeName === self.foreignKey || attributeName === self.otherKey) {
+        // this key is still needed as it's part of the association
+        // so just set primaryKey to false
+        attribute.primaryKey = false;
+      }
+      else {
+        delete self.through.model.rawAttributes[attributeName];
+      }
       self.primaryKeyDeleted = true;
     }
   });

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

@@ -1373,7 +1373,7 @@ describe(Support.getTestDialectTeaser('BelongsToMany'), function() {
       this.User.belongsToMany(this.Task, { through: this.UserTasks });
       this.Task.belongsToMany(this.User, { through: this.UserTasks });
 
-      expect(Object.keys(this.UserTasks.primaryKeys)).to.deep.equal(['TaskId', 'UserId']);
+      expect(Object.keys(this.UserTasks.primaryKeys).sort()).to.deep.equal(['TaskId', 'UserId']);
     });
 
     it('keeps the primary key if it was added by the user', function() {
@@ -1426,7 +1426,7 @@ describe(Support.getTestDialectTeaser('BelongsToMany'), function() {
         this.User.belongsToMany(this.Task, { through: this.UsersTasks });
         this.Task.belongsToMany(this.User, { through: this.UsersTasks });
 
-        expect(Object.keys(this.UsersTasks.primaryKeys)).to.deep.equal(['TaskId', 'UserId']);
+        expect(Object.keys(this.UsersTasks.primaryKeys).sort()).to.deep.equal(['TaskId', 'UserId']);
 
         return Promise.all([
           this.User.create({username: 'foo'}),

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

@@ -502,4 +502,36 @@ describe(Support.getTestDialectTeaser('belongsToMany'), function() {
       expect(Instance.prototype).not.to.have.property('addSupplementeds').which.is.a.function;
     });
   });
+
+  describe('constraints', function () {
+
+    it('work properly when through is a string', function() {
+      var User = this.sequelize.define('User', {})
+       , Group = this.sequelize.define('Group', {});
+
+      User.belongsToMany(Group, { as: 'MyGroups', through: 'group_user', onUpdate: 'RESTRICT', onDelete: 'SET NULL' });
+      Group.belongsToMany(User, { as: 'MyUsers', through: 'group_user', onUpdate: 'SET NULL', onDelete: 'RESTRICT' });
+
+      expect(Group.associations.MyUsers.through.model === User.associations.MyGroups.through.model);
+      expect(Group.associations.MyUsers.through.model.rawAttributes.UserId.onUpdate).to.equal('RESTRICT');
+      expect(Group.associations.MyUsers.through.model.rawAttributes.UserId.onDelete).to.equal('SET NULL');
+      expect(Group.associations.MyUsers.through.model.rawAttributes.GroupId.onUpdate).to.equal('SET NULL');
+      expect(Group.associations.MyUsers.through.model.rawAttributes.GroupId.onDelete).to.equal('RESTRICT');
+    });
+
+    it('work properly when through is a model', function() {
+      var User = this.sequelize.define('User', {})
+       , Group = this.sequelize.define('Group', {})
+       , UserGroup = this.sequelize.define('GroupUser', {}, {tableName: 'user_groups'});
+
+      User.belongsToMany(Group, { as: 'MyGroups', through: UserGroup, onUpdate: 'RESTRICT', onDelete: 'SET NULL' });
+      Group.belongsToMany(User, { as: 'MyUsers', through: UserGroup, onUpdate: 'SET NULL', onDelete: 'RESTRICT' });
+
+      expect(Group.associations.MyUsers.through.model === User.associations.MyGroups.through.model);
+      expect(Group.associations.MyUsers.through.model.rawAttributes.UserId.onUpdate).to.equal('RESTRICT');
+      expect(Group.associations.MyUsers.through.model.rawAttributes.UserId.onDelete).to.equal('SET NULL');
+      expect(Group.associations.MyUsers.through.model.rawAttributes.GroupId.onUpdate).to.equal('SET NULL');
+      expect(Group.associations.MyUsers.through.model.rawAttributes.GroupId.onDelete).to.equal('RESTRICT');
+    });
+  });
 });