index: add composite id

schema/index.go

@@ -1,6 +1,7 @@
 package schema
 
 import (
+	"fmt"
 	"sort"
 	"strconv"
 	"strings"
@@ -31,7 +32,12 @@ func (schema *Schema) ParseIndexes() map[string]Index {
 
 	for _, field := range schema.Fields {
 		if field.TagSettings["INDEX"] != "" || field.TagSettings["UNIQUEINDEX"] != "" {
-			for _, index := range parseFieldIndexes(field) {
+			fieldIndexes, err := parseFieldIndexes(field)
+			if err != nil {
+				schema.err = err
+				break
+			}
+			for _, index := range fieldIndexes {
 				idx := indexes[index.Name]
 				idx.Name = index.Name
 				if idx.Class == "" {
@@ -82,7 +88,7 @@ func (schema *Schema) LookIndex(name string) *Index {
 	return nil
 }
 
-func parseFieldIndexes(field *Field) (indexes []Index) {
+func parseFieldIndexes(field *Field) (indexes []Index, err error) {
 	for _, value := range strings.Split(field.Tag.Get("gorm"), ";") {
 		if value != "" {
 			v := strings.Split(value, ":")
@@ -106,7 +112,20 @@ func parseFieldIndexes(field *Field) (indexes []Index) {
 				}
 
 				if name == "" {
-					name = field.Schema.namer.IndexName(field.Schema.Table, field.Name)
+					subName := field.Name
+					const key = "COMPOSITE"
+					if composite, found := settings[key]; found {
+						if len(composite) == 0 || composite == key {
+							err = fmt.Errorf(
+								"The composite tag of %s.%s cannot be empty",
+								field.Schema.Name,
+								field.Name)
+							return
+						}
+						subName = composite
+					}
+					name = field.Schema.namer.IndexName(
+						field.Schema.Table, subName)
 				}
 
 				if (k == "UNIQUEINDEX") || settings["UNIQUE"] != "" {
@@ -138,5 +157,6 @@ func parseFieldIndexes(field *Field) (indexes []Index) {
 		}
 	}
 
+	err = nil
 	return
 }