Refactor Join ON

callbacks/query.go

@@ -125,19 +125,6 @@ func BuildQuerySQL(db *gorm.DB) {
 						})
 					}
 
-					if join.On != nil {
-						primaryFields := make([]clause.Column, len(relation.FieldSchema.PrimaryFieldDBNames))
-						for idx, ref := range relation.FieldSchema.PrimaryFieldDBNames {
-							primaryFields[idx] = clause.Column{Table: tableAliasName, Name: ref}
-						}
-
-						exprs := db.Statement.BuildCondition("(?) = (?)", primaryFields, join.On)
-						joins = append(joins, clause.Join{
-							Type:  clause.LeftJoin,
-							Table: clause.Table{Name: relation.FieldSchema.Table, Alias: tableAliasName},
-							ON:    clause.Where{Exprs: exprs},
-						})
-					} else {
 					exprs := make([]clause.Expression, len(relation.References))
 					for idx, ref := range relation.References {
 						if ref.OwnPrimaryKey {
@@ -160,12 +147,26 @@ func BuildQuerySQL(db *gorm.DB) {
 						}
 					}
 
+					if join.On != nil {
+						onStmt := gorm.Statement{Table: tableAliasName, DB: db}
+						join.On.Build(&onStmt)
+						onSQL := onStmt.SQL.String()
+						vars := onStmt.Vars
+						for idx, v := range onStmt.Vars {
+							bindvar := strings.Builder{}
+							onStmt.Vars = vars[0 : idx+1]
+							db.Dialector.BindVarTo(&bindvar, &onStmt, v)
+							onSQL = strings.Replace(onSQL, bindvar.String(), "?", 1)
+						}
+
+						exprs = append(exprs, clause.Expr{SQL: onSQL, Vars: vars})
+					}
+
 					joins = append(joins, clause.Join{
 						Type:  clause.LeftJoin,
 						Table: clause.Table{Name: relation.FieldSchema.Table, Alias: tableAliasName},
 						ON:    clause.Where{Exprs: exprs},
 					})
-					}
 				} else {
 					joins = append(joins, clause.Join{
 						Expression: clause.NamedExpr{SQL: join.Name, Vars: join.Conds},

chainable_api.go

@@ -177,7 +177,9 @@ func (db *DB) Joins(query string, args ...interface{}) (tx *DB) {
 
 	if len(args) > 0 {
 		if db, ok := args[0].(*DB); ok {
-			tx.Statement.Joins = append(tx.Statement.Joins, join{Name: query, Conds: args[1:], On: db})
+			if where, ok := db.Statement.Clauses["WHERE"].Expression.(clause.Where); ok {
+				tx.Statement.Joins = append(tx.Statement.Joins, join{Name: query, Conds: args[1:], On: &where})
+			}
 			return
 		}
 	}

statement.go

@@ -50,7 +50,7 @@ type Statement struct {
 type join struct {
 	Name  string
 	Conds []interface{}
-	On    interface{}
+	On    *clause.Where
 }
 
 // StatementModifier statement modifier interface

tests/joins_test.go

@@ -109,14 +109,15 @@ func TestJoinOn(t *testing.T) {
 	DB.Save(&user)
 
 	var user1 User
-	onQuery := DB.Select("id").Where("user_id = users.id AND name = ?", "joins-on_pet_1").Model(&Pet{})
+	onQuery := DB.Where(&Pet{Name: "joins-on_pet_1"})
 
 	if err := DB.Joins("NamedPet", onQuery).Where("users.name = ?", user.Name).First(&user1).Error; err != nil {
 		t.Fatalf("Failed to load with joins on, got error: %v", err)
 	}
+
 	AssertEqual(t, user1.NamedPet.Name, "joins-on_pet_1")
 
-	onQuery2 := DB.Select("id").Where("user_id = users.id AND name = ?", "joins-on_pet_2").Model(&Pet{})
+	onQuery2 := DB.Where(&Pet{Name: "joins-on_pet_2"})
 	var user2 User
 	if err := DB.Joins("NamedPet", onQuery2).Where("users.name = ?", user.Name).First(&user2).Error; err != nil {
 		t.Fatalf("Failed to load with joins on, got error: %v", err)