Add 'user friendly' datastore API.

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 (
+        "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
+
+// RawFilter is the function signature for a filter RDS 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 {
+        if f, ok := c.Value(rawDatastoreKey).(RawFactory); ok && f != nil {
+                return f(c)
+        }
+        return nil
+}
+
+// GetRaw gets the RawInterface implementation from context.
+func GetRaw(c context.Context) RawInterface {
+        ret := getUnfiltered(c)
+        if ret == nil {
+                return nil
+        }
+        for _, f := range getCurFilters(c) {
+                ret = f(c, ret)
+        }
+        return applyCheckFilter(c, ret)
+}
+
+// Get gets the Interface implementation from context.
+func Get(c context.Context) Interface {
+        return &datastoreImpl{GetRaw(c)}
+}
+
+// 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 })
+}
+
+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)
+}