Fix Count with Select when Model not specfied, close #3220

finisher_api.go

@@ -274,11 +274,18 @@ func (db *DB) Count(count *int64) (tx *DB) {
 		expr := clause.Expr{SQL: "count(1)"}
 
 		if len(tx.Statement.Selects) == 1 {
+			dbName := tx.Statement.Selects[0]
 			if tx.Statement.Parse(tx.Statement.Model) == nil {
-				if f := tx.Statement.Schema.LookUpField(tx.Statement.Selects[0]); f != nil {
-					expr = clause.Expr{SQL: "COUNT(DISTINCT(?))", Vars: []interface{}{clause.Column{Name: f.DBName}}}
+				if f := tx.Statement.Schema.LookUpField(dbName); f != nil {
+					dbName = f.DBName
 				}
 			}
+
+			if tx.Statement.Distinct {
+				expr = clause.Expr{SQL: "COUNT(DISTINCT(?))", Vars: []interface{}{clause.Column{Name: dbName}}}
+			} else {
+				expr = clause.Expr{SQL: "COUNT(?)", Vars: []interface{}{clause.Column{Name: dbName}}}
+			}
 		}
 
 		tx.Statement.AddClause(clause.Select{Expression: expr})

schema/schema.go

@@ -72,6 +72,10 @@ type Tabler interface {
 
 // get data type from dialector
 func Parse(dest interface{}, cacheStore *sync.Map, namer Namer) (*Schema, error) {
+	if dest == nil {
+		return nil, fmt.Errorf("%w: %+v", ErrUnsupportedDataType, dest)
+	}
+
 	modelType := reflect.ValueOf(dest).Type()
 	for modelType.Kind() == reflect.Slice || modelType.Kind() == reflect.Array || modelType.Kind() == reflect.Ptr {
 		modelType = modelType.Elem()

tests/count_test.go

@@ -2,6 +2,7 @@ package tests_test
 
 import (
 	"fmt"
+	"regexp"
 	"testing"
 
 	"gorm.io/gorm"
@@ -55,4 +56,15 @@ func TestCount(t *testing.T) {
 	if count3 != 2 {
 		t.Errorf("Should get correct count for count with group, but got %v", count3)
 	}
+
+	dryDB := DB.Session(&gorm.Session{DryRun: true})
+	result := dryDB.Table("users").Select("name").Count(&count)
+	if !regexp.MustCompile(`SELECT COUNT\(.name.\) FROM .*users.*`).MatchString(result.Statement.SQL.String()) {
+		t.Fatalf("Build count with select, but got %v", result.Statement.SQL.String())
+	}
+
+	result = dryDB.Table("users").Distinct("name").Count(&count)
+	if !regexp.MustCompile(`SELECT COUNT\(DISTINCT\(.name.\)\) FROM .*users.*`).MatchString(result.Statement.SQL.String()) {
+		t.Fatalf("Build count with select, but got %v", result.Statement.SQL.String())
+	}
 }