Merge pull request #1790 from sequelize/perf-groupJoinData

optimize groupJoinData to use a single loop

lib/instance.js

@@ -362,8 +362,8 @@ module.exports = (function() {
       , self = this
       , accessor = Utils._.camelize(key)
       , childOptions
-      , primaryKeyAttribute = include.model.primaryKeyAttribute
-      , isEmpty = value[0] && value[0][primaryKeyAttribute] === null;
+      , primaryKeyAttribute  = include.model.primaryKeyAttribute
+      , isEmpty;
 
     if (!isEmpty) {
       childOptions = {
@@ -382,9 +382,15 @@ module.exports = (function() {
       accessor = accessor.slice(0, 1).toLowerCase() + accessor.slice(1);
 
       if (association.isSingleAssociation) {
+        if (Array.isArray(value)) {
+          value = value[0];
+        }
+
+        isEmpty = value && value[primaryKeyAttribute] === null;
         accessor = Utils.singularize(accessor, self.Model.options.language);
-        self[accessor] = self.dataValues[accessor] = isEmpty ? null : include.model.build(value[0], childOptions);
+        self[accessor] = self.dataValues[accessor] = isEmpty ? null : include.model.build(value, childOptions);
       } else {
+        isEmpty = value[0] && value[0][primaryKeyAttribute] === null;
         self[accessor] = self.dataValues[accessor] = isEmpty ? [] : include.model.bulkBuild(value, childOptions);
       }
     }