在visual studio中刪除LINQ to SQL

Question

我在visual studio中使用LINQ to SQL與我的數據庫進行交互。 現在我添加了添加，更改等代碼到我的代碼的方法，但我不能刪除一行。 這是我的刪除方法：

public bool removeUser(User toBeRemoved)
{
    try
    {
        theDBDataContext db = new theDBDataContext();
        UserDB u = new UserDB();
        u.username = toBeRemoved.userName;
        u.password = toBeRemoved.password;
        u.role = toBeRemoved.role;
        db.UserDBs.DeleteOnSubmit(u);
        db.SubmitChanges();
        return true;
    }
    catch (Exception e)
    {
        Log.writelog("Cannot Access DB");
        return false;
    }
}

Answer 1

您必須在刪除前附加實體：

    theDBDataContext db = new theDBDataContext();
    UserDB u = new UserDB();
    u.username = toBeRemoved.userName;
    u.password = toBeRemoved.password;
    u.role = toBeRemoved.role;
    db.Orders.Attach(u, false);
    db.UserDBs.DeleteOnSubmit(u);
    db.SubmitChanges();

請參閱此處的文檔

Answer 2

您可以使用Linq的擴展方法刪除記錄。

    theDBDataContext db = new theDBDataContext();
     UserDB u = db.UserDBs.Where(u=>(u.username == toBeRemoved.userName & u.password == toBeRemoved.password & u.role==toBeRemoved.role)).FirstOrDefault(); 
     db.UserDBs.DeleteOnSubmit(u);
     db.SubmitChanges();