Fix unhandled rejections if an error occurs in a transaction that was just committed

changelog.md

@@ -2,6 +2,7 @@
 - [BUG] fix showIndexQuery so appropriate indexes are returned when a schema is used
 - [BUG] Fix addIndexQuery error when the model has a schema
 - [BUG] Fix app crash in sqlite while running in special unique constraint errors [3730](https://github.com/sequelize/sequelize/pull/3730)
+- [BUG] Fix trying to roll back a comitted transaction if an error occured while comitting resulting in an unhandled rejection [3726](https://github.com/sequelize/sequelize/pull/3726)
 
 # 2.1.3
 - [BUG] Fix regression introduced in 2.1.2: updatedAt not set anymore [3667](https://github.com/sequelize/sequelize/pull/3667)

lib/sequelize.js

@@ -1149,9 +1149,13 @@ module.exports = (function() {
             });
           });
         }).catch(function(err) {
-          transaction.rollback().finally(function () {
+          if (transaction.finished === 'commit') {
             reject(err);
-          });
+          } else {
+            transaction.rollback().finally(function () {
+              reject(err);
+            });
+          }
         });
       };
 

test/integration/transaction.test.js

@@ -73,6 +73,30 @@ describe(Support.getTestDialectTeaser('Transaction'), function() {
         expect(t.finished).to.be.equal('rollback');
       });
     });
+
+    if (dialect === 'postgres' || dialect === 'mssql') {
+      it('do not rollback if already committed', function() {
+        var SumSumSum = this.sequelize.define('transaction', {
+              value: {
+                type: Support.Sequelize.DECIMAL(10, 3),
+                field: 'value'
+              }
+            })
+          , transTest = function (val) {
+              return self.sequelize.transaction({isolationLevel: 'SERIALIZABLE'}, function(t) {
+                return SumSumSum.sum('value', {transaction: t}).then(function (balance) {
+                  return SumSumSum.create({value: -val}, {transaction: t});
+                });
+              });
+            }
+          , self = this;
+
+        return SumSumSum.sync({force: true}).then(function () {
+          return (expect(Promise.join(transTest(80), transTest(80))).to.eventually.be.rejectedWith('could not serialize access due to read/write dependencies among transactions'));
+        });
+      });
+    }
+
   });
 
   it('does not allow queries after commit', function() {

test/support.js

@@ -17,7 +17,12 @@ chai.config.includeStack = true;
 chai.should();
 
 // Make sure errors get thrown when testing
+process.on('uncaughtException', function(e, promise) {
+  console.error('An unhandled exception occured:');
+  throw e;
+});
 Sequelize.Promise.onPossiblyUnhandledRejection(function(e, promise) {
+  console.error('An unhandled rejection occured:');
   throw e;
 });
 Sequelize.Promise.longStackTraces();