Save many to many relations into join table

callback_shared.go

@@ -3,6 +3,7 @@ package gorm
 import (
 	"fmt"
 	"reflect"
+	"strings"
 )
 
 func BeginTransaction(scope *Scope) {
@@ -49,12 +50,36 @@ func SaveAfterAssociations(scope *Scope) {
 					newDB := scope.NewDB()
 					elem := value.Index(i).Addr().Interface()
 
-					if field.JoinTable != nil && field.JoinTable.foreignKey != "" {
+					if field.JoinTable != nil && field.JoinTable.joinTable == "" && field.JoinTable.foreignKey != "" {
 						newDB.NewScope(elem).SetColumn(field.JoinTable.foreignKey, scope.PrimaryKeyValue())
 					}
 
 					scope.Err(newDB.Save(elem).Error)
-					fmt.Sprintf("INSERT INTO %v (%v, %v) SELECT (%v, %v) FROM %v WHERE NOT EXISTS (SELECT * FROM %v WHERE %v = %v AND %v = %v) limit 1;")
+
+					if field.JoinTable != nil && field.JoinTable.joinTable != "" {
+						newScope := scope.New(elem)
+						joinTable := field.JoinTable.joinTable
+						foreignKey := ToSnake(field.JoinTable.foreignKey)
+						foreignValue := fmt.Sprintf("%v", scope.PrimaryKeyValue())
+						associationForeignKey := ToSnake(field.JoinTable.associationForeignKey)
+						associationForeignValue := fmt.Sprintf("%v", newScope.PrimaryKeyValue())
+
+						newScope.Raw(fmt.Sprintf(
+							"INSERT INTO %v (%v) SELECT %v %v WHERE NOT EXISTS (SELECT * FROM %v WHERE %v = %v AND %v = %v);",
+							joinTable,
+							strings.Join([]string{scope.Quote(foreignKey), scope.Quote(associationForeignKey)}, ","),
+							strings.Join([]string{newScope.AddToVars(foreignValue), newScope.AddToVars(associationForeignValue)}, ","),
+							scope.Dialect().SelectFromDummyTable(),
+							joinTable,
+							scope.Quote(foreignKey),
+							newScope.AddToVars(foreignValue),
+							scope.Quote(associationForeignKey),
+							newScope.AddToVars(associationForeignValue),
+						))
+						if _, err := scope.DB().Exec(newScope.Sql, newScope.SqlVars...); err != nil {
+							scope.Err(err)
+						}
+					}
 				}
 			default:
 				newDB := scope.NewDB()

common_dialect.go

@@ -64,6 +64,10 @@ func (s *commonDialect) ReturningStr(key string) string {
 	return ""
 }
 
+func (s *commonDialect) SelectFromDummyTable() string {
+	return ""
+}
+
 func (s *commonDialect) Quote(key string) string {
 	return fmt.Sprintf("`%s`", key)
 }

dialect.go

@@ -14,6 +14,7 @@ type Dialect interface {
 	SqlTag(value reflect.Value, size int) string
 	PrimaryKeyTag(value reflect.Value, size int) string
 	ReturningStr(key string) string
+	SelectFromDummyTable() string
 	Quote(key string) string
 	HasTable(scope *Scope, tableName string) bool
 	HasColumn(scope *Scope, tableName string, columnName string) bool

mysql.go

@@ -65,6 +65,10 @@ func (s *mysql) ReturningStr(key string) string {
 	return ""
 }
 
+func (s *mysql) SelectFromDummyTable() string {
+	return "FROM DUAL"
+}
+
 func (s *mysql) Quote(key string) string {
 	return fmt.Sprintf("`%s`", key)
 }

postgres.go

@@ -66,6 +66,10 @@ func (s *postgres) ReturningStr(key string) string {
 	return fmt.Sprintf("RETURNING \"%v\"", key)
 }
 
+func (s *postgres) SelectFromDummyTable() string {
+	return ""
+}
+
 func (s *postgres) Quote(key string) string {
 	return fmt.Sprintf("\"%s\"", key)
 }

scope.go

@@ -269,8 +269,8 @@ func (scope *Scope) Fields() []*Field {
 
 			// parse association
 			typ := indirectValue.Type()
-			foreignKey := settings["FOREIGNKEY"]
-			associationForeignKey := settings["ASSOCIATIONFOREIGNKEY"]
+			foreignKey := SnakeToUpperCamel(settings["FOREIGNKEY"])
+			associationForeignKey := SnakeToUpperCamel(settings["ASSOCIATIONFOREIGNKEY"])
 			many2many := settings["MANY2MANY"]
 
 			switch indirectValue.Kind() {

scope_private.go

@@ -432,6 +432,19 @@ func (scope *Scope) createTable() *Scope {
 		if !field.IsIgnored && len(field.SqlTag) > 0 {
 			sqls = append(sqls, scope.Quote(field.DBName)+" "+field.SqlTag)
 		}
+		if field.JoinTable != nil && field.JoinTable.joinTable != "" {
+			if !scope.Dialect().HasTable(scope, field.JoinTable.joinTable) {
+				newScope := scope.db.NewScope("")
+				primaryKeySqlType := scope.Dialect().SqlTag(reflect.ValueOf(scope.PrimaryKeyValue()), 255)
+				newScope.Raw(fmt.Sprintf("CREATE TABLE %v (%v)",
+					field.JoinTable.joinTable,
+					strings.Join([]string{
+						scope.Quote(ToSnake(field.JoinTable.foreignKey)) + " " + primaryKeySqlType,
+						scope.Quote(ToSnake(field.JoinTable.associationForeignKey)) + " " + primaryKeySqlType}, ",")),
+				).Exec()
+				scope.Err(newScope.db.Error)
+			}
+		}
 	}
 	scope.Raw(fmt.Sprintf("CREATE TABLE %v (%v)", scope.QuotedTableName(), strings.Join(sqls, ","))).Exec()
 	return scope

sqlite3.go

@@ -56,6 +56,10 @@ func (s *sqlite3) ReturningStr(key string) string {
 	return ""
 }
 
+func (s *sqlite3) SelectFromDummyTable() string {
+	return ""
+}
+
 func (s *sqlite3) Quote(key string) string {
 	return fmt.Sprintf("\"%s\"", key)
 }