Auto-project on distinct inequality fields.

service/datastore/query.go

Index: service/datastore/query.go
diff --git a/service/datastore/query.go b/service/datastore/query.go
index fc30f5f686808fc6f697a000c6be3bdf94e0cf65..2e60b90cda8e90ce8fe0b95f88a21635cd6d3dcd 100644
--- a/service/datastore/query.go
+++ b/service/datastore/query.go
@@ -573,6 +573,12 @@ func (q *Query) Finalize() (*FinalizedQuery, error) {
 	if q.project != nil {
 		ret.project = q.project.ToSlice()
 		ret.distinct = q.distinct && q.project.Len() > 0
+
+		// If we're DISTINCT && have an inequality filter, we must project that
+		// inequality property as well.
+		if ret.distinct && ret.ineqFiltProp != "" && !q.project.Has(ret.ineqFiltProp) {
+			ret.project = append([]string{ret.ineqFiltProp}, ret.project...)
+		}
 	}
 
 	seenOrders := stringset.New(len(q.order))