diff --git a/dialect.go b/dialect.go
index 5f6439c1..506a6e86 100644
--- a/dialect.go
+++ b/dialect.go
@@ -72,6 +72,12 @@ func RegisterDialect(name string, dialect Dialect) {
 	dialectsMap[name] = dialect
 }
 
+// GetDialect gets the dialect for the specified dialect name
+func GetDialect(name string) (dialect Dialect, ok bool) {
+	dialect, ok = dialectsMap[name]
+	return
+}
+
 // ParseFieldStructForDialect get field's sql data type
 var ParseFieldStructForDialect = func(field *StructField, dialect Dialect) (fieldValue reflect.Value, sqlType string, size int, additionalType string) {
 	// Get redirected field type
diff --git a/dialects/mssql/mssql.go b/dialects/mssql/mssql.go
index e0606465..a8d3c45a 100644
--- a/dialects/mssql/mssql.go
+++ b/dialects/mssql/mssql.go
@@ -130,7 +130,14 @@ func (s mssql) RemoveIndex(tableName string, indexName string) error {
 }
 
 func (s mssql) HasForeignKey(tableName string, foreignKeyName string) bool {
-	return false
+	var count int
+	currentDatabase, tableName := currentDatabaseAndTable(&s, tableName)
+	s.db.QueryRow(`SELECT count(*) 
+	FROM sys.foreign_keys as F inner join sys.tables as T on F.parent_object_id=T.object_id 
+		inner join information_schema.tables as I on I.TABLE_NAME = T.name 
+	WHERE F.name = ? 
+		AND T.Name = ? AND I.TABLE_CATALOG = ?;`, foreignKeyName, tableName, currentDatabase).Scan(&count)
+	return count > 0
 }
 
 func (s mssql) HasTable(tableName string) bool {
diff --git a/main.go b/main.go
index c26e05c8..25c3a06b 100644
--- a/main.go
+++ b/main.go
@@ -61,6 +61,8 @@ func Open(dialect string, args ...interface{}) (db *DB, err error) {
 		dbSQL, err = sql.Open(driver, source)
 	case SQLCommon:
 		dbSQL = value
+	default:
+		return nil, fmt.Errorf("invalid database source: %v is not a valid type", value)
 	}
 
 	db = &DB{
@@ -491,7 +493,8 @@ func (s *DB) Begin() *DB {
 
 // Commit commit a transaction
 func (s *DB) Commit() *DB {
-	if db, ok := s.db.(sqlTx); ok && db != nil {
+	var emptySQLTx *sql.Tx
+	if db, ok := s.db.(sqlTx); ok && db != nil && db != emptySQLTx {
 		s.AddError(db.Commit())
 	} else {
 		s.AddError(ErrInvalidTransaction)
@@ -501,7 +504,8 @@ func (s *DB) Commit() *DB {
 
 // Rollback rollback a transaction
 func (s *DB) Rollback() *DB {
-	if db, ok := s.db.(sqlTx); ok && db != nil {
+	var emptySQLTx *sql.Tx
+	if db, ok := s.db.(sqlTx); ok && db != nil && db != emptySQLTx {
 		s.AddError(db.Rollback())
 	} else {
 		s.AddError(ErrInvalidTransaction)
diff --git a/main_test.go b/main_test.go
index 66c46af0..265e0be7 100644
--- a/main_test.go
+++ b/main_test.go
@@ -8,6 +8,7 @@ import (
 	"path/filepath"
 	"reflect"
 	"strconv"
+	"strings"
 	"testing"
 	"time"
 
@@ -79,6 +80,22 @@ func OpenTestConnection() (db *gorm.DB, err error) {
 	return
 }
 
+func TestOpen_ReturnsError_WithBadArgs(t *testing.T) {
+	stringRef := "foo"
+	testCases := []interface{}{42, time.Now(), &stringRef}
+	for _, tc := range testCases {
+		t.Run(fmt.Sprintf("%v", tc), func(t *testing.T) {
+			_, err := gorm.Open("postgresql", tc)
+			if err == nil {
+				t.Error("Should got error with invalid database source")
+			}
+			if !strings.HasPrefix(err.Error(), "invalid database source:") {
+				t.Errorf("Should got error starting with \"invalid database source:\", but got %q", err.Error())
+			}
+		})
+	}
+}
+
 func TestStringPrimaryKey(t *testing.T) {
 	type UUIDStruct struct {
 		ID   string `gorm:"primary_key"`
diff --git a/scope.go b/scope.go
index 2f39e073..397ccf0b 100644
--- a/scope.go
+++ b/scope.go
@@ -1215,7 +1215,7 @@ func (scope *Scope) addForeignKey(field string, dest string, onDelete string, on
 }
 
 func (scope *Scope) removeForeignKey(field string, dest string) {
-	keyName := scope.Dialect().BuildKeyName(scope.TableName(), field, dest)
+	keyName := scope.Dialect().BuildKeyName(scope.TableName(), field, dest, "foreign")
 
 	if !scope.Dialect().HasForeignKey(scope.TableName(), keyName) {
 		return