Add ability to override just the metadata in a struct.

service/datastore/pls_test.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.
 
 // adapted from github.com/golang/appengine/datastore
 
 package datastore
 
 import (
         "bytes"
@@ skipping 519 matching lines @@
 }
 
 type DerivedKey struct {
         K *Key
 }
 
 type IfaceKey struct {
         K *Key
 }
 
+type IDParser struct {
+        _kind string `gae:"$kind,CoolKind"`
+
+        // real $id is myParentName|myID
+        parent string `gae:"-"`
+        id     int64  `gae:"-"`
+}
+
+var _ MetaGetterSetter = (*IDParser)(nil)
+
+func (i *IDParser) getFullID() string {
+        return fmt.Sprintf("%s|%d", i.parent, i.id)
+}
+
+func (i *IDParser) GetAllMeta() PropertyMap {
+        pm := PropertyMap{}
+        pm.SetMeta("id", i.getFullID())
+        return pm
+}
+
+func (i *IDParser) GetMeta(key string) (interface{}, error) {
+        if key == "id" {
+                return i.getFullID(), nil
+        }
+        return nil, ErrMetaFieldUnset
+}
+
+func (i *IDParser) GetMetaDefault(key string, dflt interface{}) interface{} {
+        return GetMetaDefaultImpl(i.GetMeta, key, dflt)
+}
+
+func (i *IDParser) SetMeta(key string, value interface{}) (err error) {
+        if key == "id" {
+                // let the panics flooowwww
+                vS := strings.SplitN(value.(string), "|", 2)
+                i.parent = vS[0]
+                i.id, err = strconv.ParseInt(vS[1], 10, 64)
+                return
+        }
+        return ErrMetaFieldUnset
+}
+
+type KindOverride struct {
+        ID int64 `gae:"$id"`
+
+        customKind string `gae:"-"`
+}
+
+var _ MetaGetterSetter = (*KindOverride)(nil)
+
+func (i *KindOverride) GetAllMeta() PropertyMap {
+        pm := PropertyMap{}
+        if i.customKind != "" {
+                pm.SetMeta("kind", i.customKind)
+        }
+        return pm
+}
+
+func (i *KindOverride) GetMeta(key string) (interface{}, error) {
+        if key == "kind" && i.customKind != "" {
+                return i.customKind, nil
+        }
+        return nil, ErrMetaFieldUnset
+}
+
+func (i *KindOverride) GetMetaDefault(key string, dflt interface{}) interface{} {
+        return GetMetaDefaultImpl(i.GetMeta, key, dflt)
+}
+
+func (i *KindOverride) SetMeta(key string, value interface{}) error {
+        if key == "kind" {
+                kind := value.(string)
+                if kind != "KindOverride" {
+                        i.customKind = kind
+                } else {
+                        i.customKind = ""
+                }
+                return nil
+        }
+        return ErrMetaFieldUnset
+}
+
 type testCase struct {
         desc       string
         src        interface{}
         want       interface{}
         plsErr     string
         saveErr    string
         plsLoadErr string
         loadErr    string
 }
 
@@ skipping 1161 matching lines @@
                         So(v, ShouldEqual, int64(10))
                 })
 
                 Convey("Bad default meta type", func() {
                         type BadDefault struct {
                                 Val time.Time `gae:"$meta,tomorrow"`
                         }
                         pls := GetPLS(&BadDefault{})
                         So(pls.Problem().Error(), ShouldContainSubstring, "bad type")
                 })
+
+                Convey("MetaGetterSetter implementation (IDParser)", func() {
+                        idp := &IDParser{parent: "moo", id: 100}
+                        pls := GetPLS(idp)
+                        So(pls.GetMetaDefault("id", ""), ShouldEqual, "moo|100")
+                        So(pls.GetMetaDefault("kind", ""), ShouldEqual, "CoolKind")
+
+                        So(pls.SetMeta("kind", "Something"), ShouldErrLike, "unexported field")
+                        So(pls.SetMeta("id", "happy|27"), ShouldBeNil)
+
+                        So(idp.parent, ShouldEqual, "happy")
+                        So(idp.id, ShouldEqual, 27)
+
+                        So(pls.GetAllMeta(), ShouldResemble, PropertyMap{
+                                "$id":   {MkPropertyNI("happy|27")},
+                                "$kind": {MkPropertyNI("CoolKind")},
+                        })
+                })
+
+                Convey("MetaGetterSetter implementation (KindOverride)", func() {
+                        ko := &KindOverride{ID: 20}
+                        pls := GetPLS(ko)
+                        So(pls.GetMetaDefault("kind", ""), ShouldEqual, "KindOverride")
+
+                        ko.customKind = "something"
+                        So(pls.GetMetaDefault("kind", ""), ShouldEqual, "something")
+
+                        So(pls.SetMeta("kind", "Nerp"), ShouldBeNil)
+                        So(ko.customKind, ShouldEqual, "Nerp")
+
+                        So(pls.SetMeta("kind", "KindOverride"), ShouldBeNil)
+                        So(ko.customKind, ShouldEqual, "")
+
+                        So(pls.GetAllMeta(), ShouldResemble, PropertyMap{
+                                "$id":   {MkPropertyNI(20)},
+                                "$kind": {MkPropertyNI("KindOverride")},
+                        })
+                        ko.customKind = "wut"
+                        So(pls.GetAllMeta(), ShouldResemble, PropertyMap{
+                                "$id":   {MkPropertyNI(20)},
+                                "$kind": {MkPropertyNI("wut")},
+                        })
+                })
         })
 }