From 8e7d807ebf902bf239ac9ccd509b42659ee378ba Mon Sep 17 00:00:00 2001
From: Nathan Osman <nathan@quickmediasolutions.com>
Date: Fri, 22 Dec 2017 17:59:15 -0800
Subject: [PATCH] Allow name of column to be customized to support
 self-referencing many2many fields.

---
 customize_column_test.go | 22 ++++++++++++++++++++++
 join_table_handler.go    | 19 ++++++++++++++++++-
 model_struct.go          | 15 ++++++++++++++-
 3 files changed, 54 insertions(+), 2 deletions(-)

diff --git a/customize_column_test.go b/customize_column_test.go
index ddb536b8..c96b2d40 100644
--- a/customize_column_test.go
+++ b/customize_column_test.go
@@ -279,3 +279,25 @@ func TestBelongsToWithPartialCustomizedColumn(t *testing.T) {
 		t.Errorf("should preload discount from coupon")
 	}
 }
+
+type SelfReferencingUser struct {
+	gorm.Model
+	Friends []*SelfReferencingUser `gorm:"many2many:UserFriends;AssociationForeignKey:ID=friend_id"`
+}
+
+func TestSelfReferencingMany2ManyColumn(t *testing.T) {
+	DB.DropTable(&SelfReferencingUser{}, "UserFriends")
+	DB.AutoMigrate(&SelfReferencingUser{})
+
+	friend := SelfReferencingUser{}
+	if err := DB.Create(&friend).Error; err != nil {
+		t.Errorf("no error should happen, but got %v", err)
+	}
+
+	user := SelfReferencingUser{
+		Friends: []*SelfReferencingUser{&friend},
+	}
+	if err := DB.Create(&user).Error; err != nil {
+		t.Errorf("no error should happen, but got %v", err)
+	}
+}
diff --git a/join_table_handler.go b/join_table_handler.go
index 2d1a5055..b4be6cf9 100644
--- a/join_table_handler.go
+++ b/join_table_handler.go
@@ -109,7 +109,24 @@ func (s JoinTableHandler) getSearchMap(db *DB, sources ...interface{}) map[strin
 // Add create relationship in join table for source and destination
 func (s JoinTableHandler) Add(handler JoinTableHandlerInterface, db *DB, source interface{}, destination interface{}) error {
 	scope := db.NewScope("")
-	searchMap := s.getSearchMap(db, source, destination)
+	searchMap := map[string]interface{}{}
+
+	// getSearchMap() cannot be used here since the source and destination
+	// model types may be identical
+
+	sourceScope := db.NewScope(source)
+	for _, foreignKey := range s.Source.ForeignKeys {
+		if field, ok := sourceScope.FieldByName(foreignKey.AssociationDBName); ok {
+			searchMap[foreignKey.DBName] = field.Field.Interface()
+		}
+	}
+
+	destinationScope := db.NewScope(destination)
+	for _, foreignKey := range s.Destination.ForeignKeys {
+		if field, ok := destinationScope.FieldByName(foreignKey.AssociationDBName); ok {
+			searchMap[foreignKey.DBName] = field.Field.Interface()
+		}
+	}
 
 	var assignColumns, binVars, conditions []string
 	var values []interface{}
diff --git a/model_struct.go b/model_struct.go
index 315028c4..463ec517 100644
--- a/model_struct.go
+++ b/model_struct.go
@@ -289,11 +289,24 @@ func (scope *Scope) GetModelStruct() *ModelStruct {
 									}
 
 									for _, name := range associationForeignKeys {
+
+										// In order to allow self-referencing many2many tables, the name
+										// may be followed by "=" to allow renaming the column
+										parts := strings.Split(name, "=")
+										name = parts[0]
+
 										if field, ok := toScope.FieldByName(name); ok {
 											// association foreign keys (db names)
 											relationship.AssociationForeignFieldNames = append(relationship.AssociationForeignFieldNames, field.DBName)
+
+											// If a new name was provided for the field, use it
+											name = field.DBName
+											if len(parts) > 1 {
+												name = parts[1]
+											}
+
 											// join table foreign keys for association
-											joinTableDBName := ToDBName(elemType.Name()) + "_" + field.DBName
+											joinTableDBName := ToDBName(elemType.Name()) + "_" + name
 											relationship.AssociationForeignDBNames = append(relationship.AssociationForeignDBNames, joinTableDBName)
 										}
 									}