使用 LINQ 删除 SQL in visual studio

Question

我在 visual studio 中使用 LINQ to SQL 与我的数据库进行交互。现在我添加了添加、更改等方法到我的代码，但我无法删除一行。这是我的删除方法：

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

您必须在删除之前附加实体：

    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();

见documentation here。

Answer 2

您可以使用Linq的扩展方法来删除记录。

    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();

使用 LINQ 删除 SQL in visual studio

deletion with LINQ to SQL in visual studio

.net

c#

linq

linq-to-sql