fix `addColumn` with reference not add reference in mysql

changelog.md

 # Future
+- [FIXED] `addColumn` with reference in mysql [#5592](https://github.com/sequelize/sequelize/issues/5592)
 - [ADDED] rejectOnEmpty mode [#272](https://github.com/sequelize/sequelize/issues/272) [#5480](https://github.com/sequelize/sequelize/issues/5480)
 - [ADDED] `beforeCount` hook [#5209](https://github.com/sequelize/sequelize/pull/5209)
 - [ADDED] `validationFailed` hook [#1626](https://github.com/sequelize/sequelize/issues/1626)

lib/dialects/mysql/query-generator.js

@@ -102,7 +102,8 @@ var QueryGenerator = {
       , attribute = Utils._.template('<%= key %> <%= definition %>')({
         key: this.quoteIdentifier(key),
         definition: this.attributeToSQL(dataType, {
-          context: 'addColumn'
+          context: 'addColumn',
+          foreignKey: key
         })
       });
 
@@ -229,7 +230,7 @@ var QueryGenerator = {
     return Utils._.template(sql)({ tableName: this.quoteIdentifiers(tableName), indexName: indexName });
   },
 
-  attributeToSQL: function(attribute) {
+  attributeToSQL: function(attribute, options) {
     if (!Utils._.isPlainObject(attribute)) {
       attribute = {
         type: attribute
@@ -265,6 +266,16 @@ var QueryGenerator = {
 
     if (attribute.references) {
       attribute = Utils.formatReferences(attribute);
+
+      if (options && options.context === 'addColumn' && options.foreignKey) {
+        var attrName = options.foreignKey;
+
+        template += Utils._.template(', ADD CONSTRAINT <%= fkName %> FOREIGN KEY (<%= attrName %>)')({
+          fkName: this.quoteIdentifier(attrName + '_foreign_idx'),
+          attrName: this.quoteIdentifier(attrName)
+        });
+      }
+
       template += ' REFERENCES ' + this.quoteTable(attribute.references.model);
 
       if (attribute.references.key) {

test/unit/sql/add-column.test.js

+'use strict';
+
+/* jshint -W030, -W110 */
+var Support   = require(__dirname + '/../support')
+  , DataTypes = require('../../../lib/data-types')
+  , expectsql = Support.expectsql
+  , current   = Support.sequelize
+  , sql       = current.dialect.QueryGenerator;
+
+
+if (current.dialect.name === 'mysql') {
+  describe(Support.getTestDialectTeaser('SQL'), function() {
+    describe('addColumn', function () {
+
+      var Model = current.define('users', {
+        id: {
+          type: DataTypes.INTEGER,
+          primaryKey: true,
+          autoIncrement: true
+        }
+      }, { timestamps: false });
+
+      it('properly generate alter queries', function(){
+        return expectsql(sql.addColumnQuery(Model.getTableName(), 'level_id', current.normalizeAttribute({
+          type: DataTypes.FLOAT,
+          allowNull: false,
+        })), {
+            mysql: 'ALTER TABLE `users` ADD `level_id` FLOAT NOT NULL;',
+        });
+      });
+
+      it('properly generate alter queries for foreign keys', function(){
+        return expectsql(sql.addColumnQuery(Model.getTableName(), 'level_id', current.normalizeAttribute({
+          type: DataTypes.INTEGER,
+          references: {
+            model: 'level',
+            key:   'id'
+          },
+          onUpdate: 'cascade',
+          onDelete: 'cascade'
+        })), {
+            mysql: 'ALTER TABLE `users` ADD `level_id` INTEGER, ADD CONSTRAINT `level_id_foreign_idx` FOREIGN KEY (`level_id`) REFERENCES `level` (`id`) ON DELETE CASCADE ON UPDATE CASCADE;',
+        });
+      });
+
+    });
+  });
+}