From 0e1cb6ece9d27b56ee6c1e514987175bba94711b Mon Sep 17 00:00:00 2001
From: Amit Yadav <154998+ayadav@users.noreply.github.com>
Date: Fri, 9 Feb 2018 19:50:26 +0530
Subject: [PATCH] Add support to remove foreign key constraints (#1686)

---
 main.go  |  8 ++++++++
 scope.go | 10 ++++++++++
 2 files changed, 18 insertions(+)

diff --git a/main.go b/main.go
index 16fa0b79..b23ae2f2 100644
--- a/main.go
+++ b/main.go
@@ -611,6 +611,14 @@ func (s *DB) AddForeignKey(field string, dest string, onDelete string, onUpdate
 	return scope.db
 }
 
+// RemoveForeignKey Remove foreign key from the given scope, e.g:
+//     db.Model(&User{}).RemoveForeignKey("city_id", "cities(id)")
+func (s *DB) RemoveForeignKey(field string, dest string) *DB {
+	scope := s.clone().NewScope(s.Value)
+	scope.removeForeignKey(field, dest)
+	return scope.db
+}
+
 // Association start `Association Mode` to handler relations things easir in that mode, refer: https://jinzhu.github.io/gorm/associations.html#association-mode
 func (s *DB) Association(column string) *Association {
 	var err error
diff --git a/scope.go b/scope.go
index c447d8a0..4c404b38 100644
--- a/scope.go
+++ b/scope.go
@@ -1175,6 +1175,16 @@ func (scope *Scope) addForeignKey(field string, dest string, onDelete string, on
 	scope.Raw(fmt.Sprintf(query, scope.QuotedTableName(), scope.quoteIfPossible(keyName), scope.quoteIfPossible(field), dest, onDelete, onUpdate)).Exec()
 }
 
+func (scope *Scope) removeForeignKey(field string, dest string) {
+	keyName := scope.Dialect().BuildForeignKeyName(scope.TableName(), field, dest)
+
+	if !scope.Dialect().HasForeignKey(scope.TableName(), keyName) {
+		return
+	}
+	var query = `ALTER TABLE %s DROP CONSTRAINT %s;`
+	scope.Raw(fmt.Sprintf(query, scope.QuotedTableName(), scope.quoteIfPossible(keyName))).Exec()
+}
+
 func (scope *Scope) removeIndex(indexName string) {
 	scope.Dialect().RemoveIndex(scope.TableName(), indexName)
 }