Fix addColumn query generation for enums in postgres.

lib/dialects/postgres/query-generator.js

@@ -175,17 +175,16 @@ module.exports = (function() {
 
     addColumnQuery: function(table, key, dataType) {
       var query = 'ALTER TABLE <%= table %> ADD COLUMN <%= attribute %>;'
+        , dbDataType = this.attributeToSQL(dataType, {context: 'addColumn'})
         , attribute;
 
-      if (dataType.toString() === DataTypes.ENUM.toString()) {
+      if ((dataType.type && dataType.type.toString() === DataTypes.ENUM.toString()) || dataType.toString() === DataTypes.ENUM.toString()) {
         query = this.pgEnum(table, key, dataType) + query;
       }
 
       attribute = Utils._.template('<%= key %> <%= definition %>')({
         key: this.quoteIdentifier(key),
-        definition: this.attributeToSQL(dataType, {
-          context: 'addColumn'
-        })
+        definition: this.pgDataTypeMapping(table, key, dbDataType)
       });
 
       return Utils._.template(query)({