Implement clause.Expression interface for field.Expr (#750)

do.go

@@ -256,11 +256,16 @@ func (d *DO) Order(columns ...field.Expr) Dao {
 
 func (d *DO) toOrderValue(columns ...field.Expr) string {
 	// eager build Columns
-	orderArray := make([]string, len(columns))
+	stmt := &gorm.Statement{DB: d.db.Statement.DB, Table: d.db.Statement.Table, Schema: d.db.Statement.Schema}
+
 	for i, c := range columns {
-		orderArray[i] = c.Build(d.db.Statement).String()
+		if i != 0 {
+			stmt.WriteByte(',')
+		}
+		c.Build(stmt)
 	}
-	return strings.Join(orderArray, ",")
+
+	return stmt.SQL.String()
 }
 
 // Distinct ...
@@ -281,11 +286,17 @@ func (d *DO) Group(columns ...field.Expr) Dao {
 	if len(columns) == 0 {
 		return d
 	}
-	name := string(columns[0].Build(d.db.Statement))
-	for _, col := range columns[1:] {
-		name += "," + string(col.Build(d.db.Statement))
+
+	stmt := &gorm.Statement{DB: d.db.Statement.DB, Table: d.db.Statement.Table, Schema: d.db.Statement.Schema}
+
+	for i, c := range columns {
+		if i != 0 {
+			stmt.WriteByte(',')
+		}
+		c.Build(stmt)
 	}
-	return d.getInstance(d.db.Group(name))
+
+	return d.getInstance(d.db.Group(stmt.SQL.String()))
 }
 
 // Having ...

field/expr.go

@@ -18,10 +18,12 @@ type AssignExpr interface {
 
 // Expr a query expression about field
 type Expr interface {
+	// Clause Expression interface
+	Build(clause.Builder)
+
 	As(alias string) Expr
 	ColumnName() sql
 	BuildColumn(*gorm.Statement, ...BuildOpt) sql
-	Build(*gorm.Statement) sql
 	BuildWithArgs(*gorm.Statement) (query sql, args []interface{})
 	RawExpr() expression
 
@@ -110,13 +112,15 @@ func (e expr) BuildColumn(stmt *gorm.Statement, opts ...BuildOpt) sql {
 	return sql(stmt.Quote(col))
 }
 
-func (e expr) Build(stmt *gorm.Statement) sql {
+func (e expr) Build(builder clause.Builder) {
 	if e.e == nil {
-		return sql(e.BuildColumn(stmt, WithAll))
+		if stmt, ok := builder.(*gorm.Statement); ok {
+			builder.WriteString(string(e.BuildColumn(stmt, WithAll)))
+			return
+		}
 	}
-	newStmt := &gorm.Statement{DB: stmt.DB, Table: stmt.Table, Schema: stmt.Schema}
-	e.e.Build(newStmt)
-	return sql(newStmt.SQL.String())
+
+	e.e.Build(builder)
 }
 
 func (e expr) BuildWithArgs(stmt *gorm.Statement) (sql, []interface{}) {

tests/go.mod

@@ -3,13 +3,15 @@ module gorm.io/gen/tests
 go 1.16
 
 require (
-	golang.org/x/mod v0.6.0 // indirect
-	gorm.io/driver/mysql v1.4.3
-	gorm.io/driver/sqlite v1.4.3
-	gorm.io/gen v0.3.16
-	gorm.io/gorm v1.24.0
+	github.com/mattn/go-sqlite3 v1.14.16 // indirect
+	golang.org/x/tools v0.5.0 // indirect
+	gorm.io/datatypes v1.1.0 // indirect
+	gorm.io/driver/mysql v1.4.5
+	gorm.io/driver/sqlite v1.4.4
+	gorm.io/gen v0.3.19
+	gorm.io/gorm v1.24.3
 	gorm.io/hints v1.1.1 // indirect
-	gorm.io/plugin/dbresolver v1.3.0
+	gorm.io/plugin/dbresolver v1.4.0
 )
 
 replace gorm.io/gen => ../