From c915471169b7e6696edfa9bfc2c8e7b816e70ad6 Mon Sep 17 00:00:00 2001
From: Jinzhu <wosmvp@gmail.com>
Date: Tue, 3 Nov 2020 10:30:05 +0800
Subject: [PATCH] Support Expression for OrderBy clause

---
 clause/expression.go    |  7 ++++---
 clause/order_by.go      | 21 +++++++++++++--------
 clause/order_by_test.go |  8 ++++++++
 tests/query_test.go     | 10 ++++++++++
 4 files changed, 35 insertions(+), 11 deletions(-)

diff --git a/clause/expression.go b/clause/expression.go
index 5822a314..725a4909 100644
--- a/clause/expression.go
+++ b/clause/expression.go
@@ -19,8 +19,9 @@ type NegationExpressionBuilder interface {
 
 // Expr raw expression
 type Expr struct {
-	SQL  string
-	Vars []interface{}
+	SQL                string
+	Vars               []interface{}
+	WithoutParentheses bool
 }
 
 // Build build raw expression
@@ -32,7 +33,7 @@ func (expr Expr) Build(builder Builder) {
 
 	for _, v := range []byte(expr.SQL) {
 		if v == '?' && len(expr.Vars) > idx {
-			if afterParenthesis {
+			if afterParenthesis || expr.WithoutParentheses {
 				if _, ok := expr.Vars[idx].(driver.Valuer); ok {
 					builder.AddVar(builder, expr.Vars[idx])
 				} else {
diff --git a/clause/order_by.go b/clause/order_by.go
index a8a9539a..41218025 100644
--- a/clause/order_by.go
+++ b/clause/order_by.go
@@ -7,7 +7,8 @@ type OrderByColumn struct {
 }
 
 type OrderBy struct {
-	Columns []OrderByColumn
+	Columns    []OrderByColumn
+	Expression Expression
 }
 
 // Name where clause name
@@ -17,14 +18,18 @@ func (orderBy OrderBy) Name() string {
 
 // Build build where clause
 func (orderBy OrderBy) Build(builder Builder) {
-	for idx, column := range orderBy.Columns {
-		if idx > 0 {
-			builder.WriteByte(',')
-		}
+	if orderBy.Expression != nil {
+		orderBy.Expression.Build(builder)
+	} else {
+		for idx, column := range orderBy.Columns {
+			if idx > 0 {
+				builder.WriteByte(',')
+			}
 
-		builder.WriteQuoted(column.Column)
-		if column.Desc {
-			builder.WriteString(" DESC")
+			builder.WriteQuoted(column.Column)
+			if column.Desc {
+				builder.WriteString(" DESC")
+			}
 		}
 	}
 }
diff --git a/clause/order_by_test.go b/clause/order_by_test.go
index 2ea2d192..8fd1e2a8 100644
--- a/clause/order_by_test.go
+++ b/clause/order_by_test.go
@@ -39,6 +39,14 @@ func TestOrderBy(t *testing.T) {
 			},
 			"SELECT * FROM `users` ORDER BY `name`", nil,
 		},
+		{
+			[]clause.Interface{
+				clause.Select{}, clause.From{}, clause.OrderBy{
+					Expression: clause.Expr{SQL: "FIELD(id, ?)", Vars: []interface{}{[]int{1, 2, 3}}, WithoutParentheses: true},
+				},
+			},
+			"SELECT * FROM `users` ORDER BY FIELD(id, ?,?,?)", []interface{}{1, 2, 3},
+		},
 	}
 
 	for idx, result := range results {
diff --git a/tests/query_test.go b/tests/query_test.go
index bb9aa26d..dc2907e6 100644
--- a/tests/query_test.go
+++ b/tests/query_test.go
@@ -12,6 +12,7 @@ import (
 	"time"
 
 	"gorm.io/gorm"
+	"gorm.io/gorm/clause"
 	. "gorm.io/gorm/utils/tests"
 )
 
@@ -659,6 +660,15 @@ func TestOrder(t *testing.T) {
 	if !regexp.MustCompile("SELECT \\* FROM .*users.* ORDER BY age desc,name").MatchString(result.Statement.SQL.String()) {
 		t.Fatalf("Build Order condition, but got %v", result.Statement.SQL.String())
 	}
+
+	stmt := dryDB.Clauses(clause.OrderBy{
+		Expression: clause.Expr{SQL: "FIELD(id,?)", Vars: []interface{}{[]int{1, 2, 3}}, WithoutParentheses: true},
+	}).Find(&User{}).Statement
+
+	explainedSQL := dryDB.Dialector.Explain(stmt.SQL.String(), stmt.Vars...)
+	if !regexp.MustCompile("SELECT \\* FROM .*users.* ORDER BY FIELD\\(id,1,2,3\\)").MatchString(explainedSQL) {
+		t.Fatalf("Build Order condition, but got %v", explainedSQL)
+	}
 }
 
 func TestLimit(t *testing.T) {