add @unique support in schema

schema/parse.go

@@ -73,6 +73,9 @@ func parseDirective(it *lex.ItemIterator, schema *pb.SchemaUpdate, t types.TypeI
 		schema.Count = true
 	case "upsert":
 		schema.Upsert = true
+	case "unique":
+		schema.Directive = pb.SchemaUpdate_INDEX
+		schema.Unique = true
 	case "noconflict":
 		schema.NoConflict = true
 	case "lang":
@@ -261,7 +264,7 @@ func resolveTokenizers(updates []*pb.SchemaUpdate) error {
 			continue
 		}
 
-		if len(schema.Tokenizer) == 0 && schema.Directive == pb.SchemaUpdate_INDEX {
+		if len(schema.Tokenizer) == 0 && schema.Directive == pb.SchemaUpdate_INDEX && !schema.Unique {
 			return errors.Errorf("Require type of tokenizer for pred: %s of type: %s for indexing.",
 				schema.Predicate, typ.Name())
 		} else if len(schema.Tokenizer) > 0 && schema.Directive != pb.SchemaUpdate_INDEX {

worker/mutation.go

@@ -399,11 +399,11 @@ func checkSchema(s *pb.SchemaUpdate) error {
 			x.ParseAttr(s.Predicate))
 	}
 
-	if s.Directive == pb.SchemaUpdate_INDEX && len(s.Tokenizer) == 0 {
+	if s.Directive == pb.SchemaUpdate_INDEX && len(s.Tokenizer) == 0 && !s.Unique {
 		return errors.Errorf("Tokenizer must be specified while indexing a predicate: %+v", s)
 	}
 
-	if len(s.Tokenizer) > 0 && s.Directive != pb.SchemaUpdate_INDEX {
+	if len(s.Tokenizer) > 0 && s.Directive != pb.SchemaUpdate_INDEX && !s.Unique {
 		return errors.Errorf("Directive must be SchemaUpdate_INDEX when a tokenizer is specified")
 	}
 
@@ -424,6 +424,32 @@ func checkSchema(s *pb.SchemaUpdate) error {
 			x.ParseAttr(s.Predicate))
 	}
 
+	if s.Unique {
+		if s.ValueType == pb.Posting_STRING {
+			checkTerm := func() bool {
+				for _, value := range s.Tokenizer {
+					return value == "term"
+				}
+				return false
+			}
+			if len(s.Tokenizer) == 0 {
+				s.Tokenizer = append(s.Tokenizer, "exact")
+			} else if checkTerm() {
+				return errors.New("term index is not allowed")
+			}
+		}
+		if s.ValueType == pb.Posting_INT {
+			if len(s.Tokenizer) == 0 {
+				s.Tokenizer = append(s.Tokenizer, "int")
+			}
+		}
+		if s.ValueType == pb.Posting_FLOAT {
+			if len(s.Tokenizer) == 0 {
+				s.Tokenizer = append(s.Tokenizer, "float")
+			}
+		}
+	}
+
 	t, err := schema.State().TypeOf(s.Predicate)
 	if err != nil {
 		// No schema previously defined, so no need to do checks about schema conversions.

worker/schema.go

@@ -56,7 +56,7 @@ func getSchema(ctx context.Context, s *pb.SchemaRequest) (*pb.SchemaResult, erro
 	if len(s.Fields) > 0 {
 		fields = s.Fields
 	} else {
-		fields = []string{"type", "index", "tokenizer", "reverse", "count", "list", "upsert",
+		fields = []string{"type", "index", "tokenizer", "reverse", "count", "list", "upsert", "unique",
 			"lang", "noconflict"}
 	}
 
@@ -110,6 +110,8 @@ func populateSchema(attr string, fields []string) *pb.SchemaNode {
 			schemaNode.List = pred.GetList()
 		case "upsert":
 			schemaNode.Upsert = pred.GetUpsert()
+		case "unique":
+			schemaNode.Upsert = pred.GetUnique()
 		case "lang":
 			schemaNode.Lang = pred.GetLang()
 		case "noconflict":