Add API to allow you to get the non-transactional datastore or taskqueue.

service/datastore/context.go

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package datastore
 
 import (
         "github.com/luci/gae/service/info"
         "golang.org/x/net/context"
 )
 
 type key int
 
 var (
         rawDatastoreKey       key
         rawDatastoreFilterKey key = 1
 )
 
 // RawFactory is the function signature for factory methods compatible with
-// SetRawFactory.
-type RawFactory func(context.Context) RawInterface
+// SetRawFactory. wantTxn is true if the Factory should return the datastore in
+// the current transaction, and false if the Factory should return the
+// non-transactional (root) datastore.
+type RawFactory func(c context.Context, wantTxn bool) RawInterface
 
 // RawFilter is the function signature for a RawFilter implementation. It
 // gets the current RDS implementation, and returns a new RDS implementation
 // backed by the one passed in.
 type RawFilter func(context.Context, RawInterface) RawInterface
 
 // getUnfiltered gets gets the RawInterface implementation from context without
 // any of the filters applied.
-func getUnfiltered(c context.Context) RawInterface {
+func getUnfiltered(c context.Context, wantTxn bool) RawInterface {
         if f, ok := c.Value(rawDatastoreKey).(RawFactory); ok && f != nil {
-                return f(c)
+                return f(c, wantTxn)
         }
         return nil
 }
 
-// GetRaw gets the RawInterface implementation from context.
-func GetRaw(c context.Context) RawInterface {
-        ret := getUnfiltered(c)
+// getFiltered gets the datastore (transactional or not), and applies all of
+// the currently installed filters to it.
+func getFiltered(c context.Context, wantTxn bool) RawInterface {
+        ret := getUnfiltered(c, wantTxn)
         if ret == nil {
                 return nil
         }
         for _, f := range getCurFilters(c) {
                 ret = f(c, ret)
         }
         return applyCheckFilter(c, ret)
 }
 
+// GetRaw gets the RawInterface implementation from context.
+func GetRaw(c context.Context) RawInterface {
+        return getFiltered(c, true)
+}
+
+// GetRawNoTxn gets the RawInterface implementation from context. If there's a
+// currently active transaction, this will return a non-transactional connection
+// to the datastore, otherwise this is the same as GetRaw.
+func GetRawNoTxn(c context.Context) RawInterface {
+        return getFiltered(c, false)
+}
+
 // Get gets the Interface implementation from context.
 func Get(c context.Context) Interface {
         inf := info.Get(c)
         return &datastoreImpl{
                 GetRaw(c),
                 inf.FullyQualifiedAppID(),
                 inf.GetNamespace(),
         }
 }
 
+// GetNoTxn gets the Interface implementation from context. If there's a
+// currently active transaction, this will return a non-transactional connection
+// to the datastore, otherwise this is the same as GetRaw.
+// Get gets the Interface implementation from context.
+func GetNoTxn(c context.Context) Interface {
+        inf := info.Get(c)
+        return &datastoreImpl{
+                GetRawNoTxn(c),
+                inf.FullyQualifiedAppID(),
+                inf.GetNamespace(),
+        }
+}
+
 // SetRawFactory sets the function to produce Datastore instances, as returned by
 // the GetRaw method.
 func SetRawFactory(c context.Context, rdsf RawFactory) context.Context {
         return context.WithValue(c, rawDatastoreKey, rdsf)
 }
 
 // SetRaw sets the current Datastore object in the context. Useful for testing
 // with a quick mock. This is just a shorthand SetRawFactory invocation to set
 // a factory which always returns the same object.
 func SetRaw(c context.Context, rds RawInterface) context.Context {
-        return SetRawFactory(c, func(context.Context) RawInterface { return rds })
+        return SetRawFactory(c, func(context.Context, bool) RawInterface { return rds })
 }
 
 func getCurFilters(c context.Context) []RawFilter {
         curFiltsI := c.Value(rawDatastoreFilterKey)
         if curFiltsI != nil {
                 return curFiltsI.([]RawFilter)
         }
         return nil
 }
 
 // AddRawFilters adds RawInterface filters to the context.
 func AddRawFilters(c context.Context, filts ...RawFilter) context.Context {
         if len(filts) == 0 {
                 return c
         }
         cur := getCurFilters(c)
         newFilts := make([]RawFilter, 0, len(cur)+len(filts))
         newFilts = append(newFilts, getCurFilters(c)...)
         newFilts = append(newFilts, filts...)
         return context.WithValue(c, rawDatastoreFilterKey, newFilts)
 }