如何使用GORM检查CRUD操作中的错误？

Question

The official documentation for GORM demonstrates a way in which one can test for the existence of a record, i.e.:

user := User{Name: "Jinzhu", Age: 18, Birthday: time.Now()}

// returns true if record hasn’t been saved (primary key `Id` is blank)
db.NewRecord(user) // => true

db.Create(&user)

// will return false after `user` created
db.NewRecord(user) // => false

This can be used to test indirectly for errors in record creation but reports no useful information in the event of a failure.

Having checked the source code for db.Create, there seems to be some sort of stack-frame inspection that checks for errors before proceeding, meaning that transactional errors will fail silently:

func Create(scope *Scope) {
    defer scope.Trace(NowFunc())

    if !scope.HasError() {
        // actually perform the transaction
    }
}

• Is this a bug, or am I missing something?
• How can/should I be informed of a failed transaction?
• Where can I get useful debugging information?

Answer 1

DB.Create() returns a new (cloned) gorm.DB which is a struct and has a field Error:

type DB struct {
    Value        interface{}
    Error        error
    RowsAffected int64
    // contains filtered or unexported fields
}

You can store the returned *gorm.DB value and check its DB.Error field like this:

if dbc := db.Create(&user); dbc.Error != nil {
    // Create failed, do something e.g. return, panic etc.
    return
}

If you don't need anything else from the returned gorm.DB, you can directly check its Error field:

if db.Create(&user).Error != nil {
    // Create failed, do something e.g. return, panic etc.
    return
}