Function CheckAndModifyPreDefPredicate

schema/schema.go:875–899

CheckAndModifyPreDefPredicate returns true if the initial update for the pre-defined predicate is different from the passed update. It may also modify certain predicates under specific conditions. If the passed update is not a pre-defined predicate, it returns false.

(update *pb.SchemaUpdate)

// under specific conditions.
// If the passed update is not a pre-defined predicate, it returns false.
func CheckAndModifyPreDefPredicate(update *pb.SchemaUpdate) bool {
	// Return false for non-pre-defined predicates.
	if !x.IsPreDefinedPredicate(update.Predicate) {
		return false
	}
	ns := x.ParseNamespace(update.Predicate)
	initialSchema := CompleteInitialSchema(ns)
	for _, original := range initialSchema {
		if original.Predicate != update.Predicate {
			continue
		}

		// For the dgraph.xid predicate, only the Unique field is allowed to be changed.
		// Previously, the Unique attribute was not applied to the dgraph.xid predicate.
		// For users upgrading from a lower version, we will set Unique to true.
		if update.Predicate == x.NamespaceAttr(ns, "dgraph.xid") && !update.Unique {
			if isDgraphXidChangeValid(original, update) {
				update.Unique = true
				return false
			}
		}
		return !proto.Equal(original, update)
	}
	return true
}

// isDgraphXidChangeValid returns true if the change in the dgraph.xid predicate is valid.
func isDgraphXidChangeValid(original, update *pb.SchemaUpdate) bool {