Merge pull request #28

add save() test case and update readme

README.md

@@ -20,14 +20,19 @@ DB.First(&user)
 DB.Model(&user).Update("age", 18)
 // UPDATE `users` SET `age`=18,`version`=`version`+1 WHERE `users`.`version` = 1 AND `id` = 1
 
+// Ignoring the optimistic lock check.
 DB.Unscoped().Model(&user).Update("age", 18)
 // UPDATE `users` SET `age`=18,`version`=`version`+1 WHERE `id` = 1
 
-// The Model's Version value passed in to Updates will be ignored
+// Ignoring the passed Version value.
 DB.Model(&user).Updates(&User{Age: 18, Version: optimisticlock.Version{Int64: 1}})
 // UPDATE `users` SET `age`=18,`version`=`version`+1 WHERE `users`.`version` = 3 AND `id` = 1
 
-// Model's Version is zero, then no condition will be added to the WHERE
+// If the Model's Version value is zero, Without considering optimistic lock check.
 DB.Model(&User{}).Where("id = 1").Update("age", 12)
 // UPDATE `users` SET `age`=12,`version`=`version`+1 WHERE id = 1
+
+// When want to use GORM's Save method, need to call Select. Otherwise, will return primary key duplicate error.
+// The Select param is the fields that you want to update or "*".
+DB.Model(&user).Select("*").Updates(&User{Age: 18})
 ```

version_test.go

@@ -109,6 +109,12 @@ func TestVersion(t *testing.T) {
 	require.Equal(t, date, user.UpdatedAt)
 	DB.NowFunc = time.Now
 
+	// Call Select method. Otherwise, will return primary key duplicate error.
+	user.Name = "lucky"
+	tx := DB.Select("*").Save(&user)
+	require.Nil(t, tx.Error)
+	require.Equal(t, int64(0), tx.RowsAffected)
+
 	// support create
 	users := []User{{Name: "foo", Age: 30}, {Name: "bar", Age: 40, Version: Version{Int64: 100}}}
 	DB.Create(&users)