do not initialize task cache volumes for one off builds

You cannot have task caches for one off builds, but we were never
disallowing that before.

Also, we shouldn't be ignoring foreign key violations and doing a Safe
Retry.

#230

Signed-off-by: Maria Shaldibina <mshaldibina@pivotal.io>

db/worker_task_cache_factory.go

@@ -126,10 +126,6 @@ func (wtc WorkerTaskCache) FindOrCreate(
 				QueryRow().
 				Scan(&id)
 			if err != nil {
-				if pqErr, ok := err.(*pq.Error); ok && pqErr.Code.Name() == "foreign_key_violation" {
-					return nil, ErrSafeRetryFindOrCreate
-				}
-
 				if pqErr, ok := err.(*pq.Error); ok && pqErr.Code.Name() == "unique_violation" {
 					return nil, ErrSafeRetryFindOrCreate
 				}

exec/task_action.go

@@ -403,19 +403,22 @@ func (action *TaskAction) registerOutputs(logger lager.Logger, repository *worke
 		}
 	}
 
-	logger.Debug("initializing-caches", lager.Data{"caches": config.Caches})
+	// Do not initialize caches for one-off builds
+	if action.jobID != 0 {
+		logger.Debug("initializing-caches", lager.Data{"caches": config.Caches})
 
-	for _, cacheConfig := range config.Caches {
-		for _, volumeMount := range volumeMounts {
-			if volumeMount.MountPath == filepath.Join(action.artifactsRoot, cacheConfig.Path) {
-				logger.Debug("initializing-cache", lager.Data{"path": volumeMount.MountPath})
+		for _, cacheConfig := range config.Caches {
+			for _, volumeMount := range volumeMounts {
+				if volumeMount.MountPath == filepath.Join(action.artifactsRoot, cacheConfig.Path) {
+					logger.Debug("initializing-cache", lager.Data{"path": volumeMount.MountPath})
 
-				err := volumeMount.Volume.InitializeTaskCache(logger, action.jobID, action.stepName, cacheConfig.Path, bool(action.privileged))
-				if err != nil {
-					return err
-				}
+					err := volumeMount.Volume.InitializeTaskCache(logger, action.jobID, action.stepName, cacheConfig.Path, bool(action.privileged))
+					if err != nil {
+						return err
+					}
 
-				continue
+					continue
+				}
 			}
 		}
 	}

exec/task_action_test.go

@@ -673,6 +673,18 @@ var _ = Describe("TaskAction", func() {
 						Expect(cachePath).To(Equal("some-path-2"))
 						Expect(p).To(Equal(bool(privileged)))
 					})
+
+					Context("when task does not belong to job (one-off build)", func() {
+						BeforeEach(func() {
+							jobID = 0
+						})
+
+						It("does not initialize caches", func() {
+							Eventually(process.Wait()).Should(Receive(BeNil()))
+							Expect(fakeVolume1.InitializeTaskCacheCallCount()).To(Equal(0))
+							Expect(fakeVolume2.InitializeTaskCacheCallCount()).To(Equal(0))
+						})
+					})
 				})
 
 				Context("when the configuration specifies paths for outputs", func() {