我的查找功能是否遵循最佳实践

Question

I want to make sure my query to find models by ID is correct as I will be using this same pattern for all my structs/models.

func (dbs *DbService) GetUserLocationId(locationId int) (User, error) {
    var model User
    if dbs.deps.db.Where("location_id = ?", locationId).Find(&model).RecordNotFound() {
        return model, errors.New("User not found")
    }
    return model, nil
}

So a common usecase in a web application is to lookup a model, if it does not exist that I will insert a new record.

using the above I will do:

user, err := GetUserLocationById(123)
if err != nil {
  err := InsertNewUser(user)
}

Now what thing I am struggling with is this. If the errors is not nil, then I should insert a new user. But what if the error is because my query inside the function GetUserLocationById has the wrong column name? I dont' want to start inserting rows when they really do exist.

Looking for some advice to make sure I am doing this correctly.

Answer 1

Regarding "best practices", it's better to post under the dedicated SO website.

var ErrUserNotFound = errors.New("User not found")

func (dbs *DbService) GetUserLocationId(locationId int) (user User, err error)
    record := dbs.deps.db.Where("location_id = ?", locationId).Find(&user)
    if record.RecordNotFound() {
        err = ErrUserNotFound
    }
    return
}

Okay this is closer to the GO "best practices" standards IMHO. It's considered good practices to create package error values for commonly returned errors. It helps the caller handle each case properly (should there be), but it's not really the case here.

For the other snippet, you really won't want to do this like that. First of all you omitted the pointer receiver for both methods GetUserLocationById and InsertNewUser. Then, you usually don't want to shadow the parent's scope err variable, but it's ok here...

user, err := dbs.GetUserLocationById(123)
if err != nil {
   err = dbs.InsertNewUser(user)
   // handle err here
}

Anyways, I think that doing this with errors is too bad for there are no really other possibilities than "ErrUserNotFound" here. I would advise going for a ok boolean instead.

func (dbs *DbService) GetUserLocationId(locationId int) (user User, ok bool)
    record := dbs.deps.db.Where("location_id = ?", locationId).Find(&user)
    ok = !record.RecordNotFound()
    return
}

and then

var user User
if user, ok := dbs.GetUserLocationId(123); !ok {
    if err := dbs.InsertNewUser(user); err != nil {
        panic(err)
    }
}