如何获得受Go-Gorm关联模式影响的行

Question

I insert a relation by the following code:

db.Where(exercise).FirstOrCreate(&exercise).Model(&User{ID: userID}).Association("Exercises").Append(&exercise)

Corresponding SQL printed by debug console to the code is:

INSERT INTO `user_exercise` (`user_id`,`exercise_id`) SELECT 1,1 FROM DUAL WHERE NOT EXISTS (SELECT * FROM `user_exercise` WHERE `user_id` = 1 AND `exercise_id` = 1)  

I want know if there are new record created in user_exercise, but due to the generated SQL, if a relation in user_exercise already exists, it won't insert and produce no error.

Go-Gorm's Association object doesn't have a RowsAffected attribute, so I can't get RowsAffected from the query to confirm if a new record is created.

Though I can get RowsAffected from the first db object, like

db.Where(exercise).FirstOrCreate(&exercise).Model(&User{ID: userID}).Association("Exercises").Append(&exercise)
if db.RowsAffected == 1 {
    // do something
}

I wonder since the db is shared by all queries, if another query executed at the same time and affected rows > 0, is it safe to get RowsAffected from the global db object?

Answer 1

Assuming that the user_execise table has an unique constraint (user_id, exercise_id) the insert should return an error if you try to do it to an already created record. (Exactly what you want) So just do something like this...

db.Where(exercise).FirstOrCreate(&exercise)
ue := struct {
  UserID uint
  ExerciseID uint
}{
  UserID: userID,
  ExerciseID exercise.ID
}
if err := db.Table("user_exercise").Create(&ue).Error; err != nil {
  // will enter here if it wasn't created
}

If it doesn't returns an Error means that a new record was created