support string in include (in association field too) (#6512)

docs/docs/models-usage.md

@@ -523,6 +523,26 @@ User.findAll({ include: ['Instruments'] }).then(function(users) {
     }]
   */
 })
+
+User.findAll({ include: [{ association: 'Instruments' }] }).then(function(users) {
+  console.log(JSON.stringify(users))
+
+  /*
+    [{
+      "name": "John Doe",
+      "id": 1,
+      "createdAt": "2013-03-20T20:31:45.000Z",
+      "updatedAt": "2013-03-20T20:31:45.000Z",
+      "Instruments": [{
+        "name": "Toothpick",
+        "id": 1,
+        "createdAt": null,
+        "updatedAt": null,
+        "userId": 1
+      }]
+    }]
+  */
+})
 ```
 
 When eager loading we can also filter the associated model using `where`. This will return all `User`s in which the `where` clause of `Tool` model matches rows.

lib/model.js

@@ -182,18 +182,23 @@ class Model {
     options.include = options.include.map(include => this._conformInclude(include, self));
   }
 
-  static _conformInclude(include, self) {
-    let model;
-
-    if (include._pseudo) return include;
-
+  static _transformStringAssociation (include, self) {
     if (self && typeof include === 'string') {
       if (!self.associations.hasOwnProperty(include)) {
         throw new Error('Association with alias "' + include + '" does not exists');
       }
-      include = self.associations[include];
+      return self.associations[include];
+    }
+    return include;
   }
 
+  static _conformInclude(include, self) {
+    let model;
+
+    if (include._pseudo) return include;
+
+    include = this._transformStringAssociation(include, self);
+
     if (include instanceof Association) {
       if (self && include.target.name === self.name) {
         model = include.source;
@@ -206,6 +211,9 @@ class Model {
       include = { model: include };
     } else if (_.isPlainObject(include)) {
       if (include.association) {
+
+        include.association = this._transformStringAssociation(include.association, self);
+
         if (self && include.association.target.name === self.name) {
           model = include.association.source;
         } else {

test/unit/model/include.test.js

@@ -266,6 +266,23 @@ describe(Support.getTestDialectTeaser('Model'), function() {
           as: 'Owner'
         });
       });
+
+      it('should expand string association', function () {
+        const options = {
+          include: [{
+            association: 'Owner',
+            attributes: ['id']
+          }]
+        };
+        Sequelize.Model._conformOptions(options, this.Company);
+
+        expect(options.include[0]).to.deep.equal({
+          model: this.User,
+          association: this.Company.Owner,
+          attributes: ['id'],
+          as: 'Owner'
+        });
+      });
     });
 
     describe('subQuery', function () {