Support calling setAssociation twice on hasOne. Closes #5315

changelog.md

 # Future
 # Future
 - [FIXED] Confirmed that values modified in validation hooks are preserved [#3534](https://github.com/sequelize/sequelize/issues/3534)
 - [FIXED] Confirmed that values modified in validation hooks are preserved [#3534](https://github.com/sequelize/sequelize/issues/3534)
 - [FIXED] Support lower case type names in SQLite [#5482](https://github.com/sequelize/sequelize/issues/5482)
 - [FIXED] Support lower case type names in SQLite [#5482](https://github.com/sequelize/sequelize/issues/5482)
+- [FIXED] Support calling `setAssociation` twice on `hasOne` [#5315](https://github.com/sequelize/sequelize/issues/5315)
 - [INTERNALS] Removed dependency on wellknown in favor of terraformer-wkt-parser
 - [INTERNALS] Removed dependency on wellknown in favor of terraformer-wkt-parser
 - [ADDED] Benchmarking feature [#2494](https://github.com/sequelize/sequelize/issues/2494)
 - [ADDED] Benchmarking feature [#2494](https://github.com/sequelize/sequelize/issues/2494)
 
 

lib/associations/has-one.js

@@ -173,12 +173,18 @@ HasOne.prototype.injectSetter = function(instancePrototype) {
   var association = this;
   var association = this;
 
 
   instancePrototype[this.accessors.set] = function(associatedInstance, options) {
   instancePrototype[this.accessors.set] = function(associatedInstance, options) {
-    var instance = this;
+    var instance = this,
+      alreadyAssociated;
 
 
     options = options || {};
     options = options || {};
     options.scope = false;
     options.scope = false;
     return instance[association.accessors.get](options).then(function(oldInstance) {
     return instance[association.accessors.get](options).then(function(oldInstance) {
-      if (oldInstance) {
+      // TODO Use equals method once #5605 is resolved
+      alreadyAssociated = oldInstance && associatedInstance && _.every(association.target.primaryKeyAttributes, function(attribute) {
+        return oldInstance.get(attribute, {raw: true}) === associatedInstance.get(attribute, {raw: true});
+      });
+
+      if (oldInstance && !alreadyAssociated) {
         oldInstance[association.foreignKey] = null;
         oldInstance[association.foreignKey] = null;
         return oldInstance.save(_.extend({}, options, {
         return oldInstance.save(_.extend({}, options, {
           fields: [association.foreignKey],
           fields: [association.foreignKey],
@@ -187,7 +193,7 @@ HasOne.prototype.injectSetter = function(instancePrototype) {
         }));
         }));
       }
       }
     }).then(function() {
     }).then(function() {
-      if (associatedInstance) {
+      if (associatedInstance && !alreadyAssociated) {
         if (!(associatedInstance instanceof association.target.Instance)) {
         if (!(associatedInstance instanceof association.target.Instance)) {
           var tmpInstance = {};
           var tmpInstance = {};
           tmpInstance[association.target.primaryKeyAttribute] = associatedInstance;
           tmpInstance[association.target.primaryKeyAttribute] = associatedInstance;

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

@@ -334,6 +334,28 @@ describe(Support.getTestDialectTeaser('BelongsTo'), function() {
         });
         });
       });
       });
     });
     });
+
+    it('supports setting same association twice', function () {
+      var Home = this.sequelize.define('home', {})
+        , User = this.sequelize.define('user');
+
+      Home.belongsTo(User);
+
+      return this.sequelize.sync({ force: true }).bind({}).then(function () {
+        return Promise.all([
+          Home.create(),
+          User.create()
+        ]);
+      }).spread(function (home, user) {
+        this.home = home;
+        this.user = user;
+        return home.setUser(user);
+      }).then(function() {
+        return this.home.setUser(this.user);
+      }).then(function () {
+        return expect(this.home.getUser()).to.eventually.have.property('id', this.user.get('id'));
+      });
+    });
   });
   });
 
 
   describe('createAssociation', function() {
   describe('createAssociation', function() {

test/integration/associations/has-one.test.js

@@ -217,6 +217,28 @@ describe(Support.getTestDialectTeaser('HasOne'), function() {
         });
         });
       });
       });
     });
     });
+
+    it('supports setting same association twice', function () {
+      var Home = this.sequelize.define('home', {})
+        , User = this.sequelize.define('user');
+
+      User.hasOne(Home);
+
+      return this.sequelize.sync({ force: true }).bind({}).then(function () {
+        return Promise.all([
+          Home.create(),
+          User.create()
+        ]);
+      }).spread(function (home, user) {
+        this.home = home;
+        this.user = user;
+        return user.setHome(home);
+      }).then(function() {
+        return this.user.setHome(this.home);
+      }).then(function () {
+        return expect(this.user.getHome()).to.eventually.have.property('id', this.home.get('id'));
+      });
+    });
   });
   });
 
 
   describe('createAssociation', function() {
   describe('createAssociation', function() {