support named params in Select API (#4142)

* adds support for named arguments in select

* changes clause identifies and adds test

Author: ratanphayade

chainable_api.go

@@ -98,7 +98,12 @@ func (db *DB) Select(query interface{}, args ...interface{}) (tx *DB) {
 				Distinct:   db.Statement.Distinct,
 				Expression: clause.Expr{SQL: v, Vars: args},
 			})
-		} else {
+		} else if strings.Count(v, "@") > 0 && len(args) > 0 {
+			tx.Statement.AddClause(clause.Select{
+				Distinct:   db.Statement.Distinct,
+				Expression: clause.NamedExpr{SQL: v, Vars: args},
+			})
+		}  else {
 			tx.Statement.Selects = []string{v}
 
 			for _, arg := range args {

clause/clause.go

@@ -62,9 +62,9 @@ func (c Clause) Build(builder Builder) {
 }
 
 const (
-	PrimaryKey   string = "@@@py@@@" // primary key
-	CurrentTable string = "@@@ct@@@" // current table
-	Associations string = "@@@as@@@" // associations
+	PrimaryKey   string = "~~~py~~~" // primary key
+	CurrentTable string = "~~~ct~~~" // current table
+	Associations string = "~~~as~~~" // associations
 )
 
 var (

tests/query_test.go

@@ -628,6 +628,12 @@ func TestSelect(t *testing.T) {
 		t.Fatalf("Build Select with func, but got %v", r.Statement.SQL.String())
 	}
 
+	// named arguments
+	r = dryDB.Table("users").Select("COALESCE(age, @default)", sql.Named("default", 42)).Find(&User{})
+	if !regexp.MustCompile(`SELECT COALESCE\(age,.*\) FROM .*users.*`).MatchString(r.Statement.SQL.String()) {
+		t.Fatalf("Build Select with func, but got %v", r.Statement.SQL.String())
+	}
+
 	if _, err := DB.Table("users").Select("COALESCE(age,?)", "42").Rows(); err != nil {
 		t.Fatalf("Failed, got error: %v", err)
 	}