SQLite.Net SQLiteException 约束

Question

I've looked here before with this error but the results won't work for me.

I have made a login form and it works fine for one time. After I logged in once and restart the app and try to log in I'm getting the error.

Function:

public int SaveUser(User user)
{
    lock (locker)
    {
        if (user.Id != 0)
        {
            database.Update(user);
            return user.Id;
        }

        else
        {
            return database.Insert(user);
        }
    }
}

User model:

[Table("User")]
public class User
{   
    [PrimaryKey, AutoIncrement, NotNull]
    public int Id { get; set; }
    [Unique]
    public string Username { get; set; }
    public string Password { get; set; }
}

Update: I hope this are the details that's needed for further help.

02-27 14:13:15.806 I/MonoDroid(23447): at SQLite.PreparedSqlLiteInsertCommand.ExecuteNonQuery (System.Object[] source) [0x00121] in /Users/vagrant/git/src/SQLite.cs:2668 02-27 14:13:15.806 I/MonoDroid(23447): at SQLite.SQLiteConnection.Insert (System.Object obj, System.String extra, System.Type objType) [0x000f4] in /Users/vagrant/git/src/SQLite.cs:1415 02-27 14:13:15.806 I/MonoDroid(23447): at SQLite.SQLiteConnection.Insert (System.Object obj) [0x00005] in /Users/vagrant/git/src/SQLite.cs:1281 02-27 14:13:15.806 I/MonoDroid(23447): at KleynGroup.Data.UserDatabaseController.SaveUser (KleynGroup.User user) [0x00038] in C:\\Users\\[name]\\source\\repos\\KleynGroup\\KleynGroup\\KleynGroup\\Data\\UserDatabaseController.cs:48

Sorry if there are a lot of mistakes. I'm new to Xamarin and still learning.

I hope you guys can help me

Answer 1

According to the error messages the exception is thrown by Insert , hence I'd assume that you are trying to insert the User ( User.Id seems to be 0 ). Anyway, since it's not a new, but an existing user name, inserting it fails because of the UNIQUE constraint of Username .

You have to make sure, that when the user is loaded and then saved, it still has the correct ID, to prevent that exception.