Re-add metadata passthrough on Get operations

service/datastore/multiarg.go

Index: service/datastore/multiarg.go
diff --git a/service/datastore/multiarg.go b/service/datastore/multiarg.go
index 494d3952c9f2ad4fc8b6eecc502053083ceeb3eb..3398b1e4ab3490aa3fba5e871f29793de044c201 100644
--- a/service/datastore/multiarg.go
+++ b/service/datastore/multiarg.go
@@ -21,26 +21,21 @@ type multiArgType struct {
 	newElem func() reflect.Value
 }
 
-func (mat *multiArgType) GetKeys(nk newKeyFunc, slice reflect.Value) ([]Key, error) {
-	ret := make([]Key, slice.Len())
-	lme := errors.LazyMultiError{Size: len(ret)}
-	for i := range ret {
+func (mat *multiArgType) GetKeysPMs(nk newKeyFunc, slice reflect.Value) ([]Key, []PropertyMap, error) {
+	retKey := make([]Key, slice.Len())
+	retPM := make([]PropertyMap, slice.Len())
+	lme := errors.LazyMultiError{Size: len(retKey)}
+	for i := range retKey {
 		key, err := mat.getKey(nk, slice.Index(i))
-		lme.Assign(i, err)
-		ret[i] = key
-	}
-	return ret, lme.Get()
-}
-
-func (mat *multiArgType) GetPMs(slice reflect.Value) ([]PropertyMap, error) {
-	ret := make([]PropertyMap, slice.Len())
-	lme := errors.LazyMultiError{Size: len(ret)}
-	for i := range ret {
-		key, err := mat.getPM(slice.Index(i))
-		lme.Assign(i, err)
-		ret[i] = key
+		if !lme.Assign(i, err) {
+			retKey[i] = key
+			pm, err := mat.getPM(slice.Index(i))
+			if !lme.Assign(i, err) {
+				retPM[i] = pm
+			}
+		}
 	}
-	return ret, lme.Get()
+	return retKey, retPM, lme.Get()
 }
 
 // parseMultiArg checks that v has type []S, []*S, []I, []P or []*P, for some