LINQ To SQL C＃更新类

Question

I have users table with generated LINQ-class with followed structure:

class User {
    int Id;
    string Login;
    string Password;
    string Mail;
    ...

Now I need to update specified columns (for ex. only Login and Password) and because I don't want to overwrite other fields, my code looks like this:

public User UpdateUser(int userId, User newUser)
{
    User user = (from u in _context.Users
                where u.Id == userId
                select u).FirstOrDefault();

    if (newUser.Login != default(string)) user.Login = newUser.Login;
    if (newUser.Mail != default(string)) user.Mail = newUser.Mail;
    if (newUser.Password != default(string)) user.Password = newUser.Password;
    ...

    _context.SubmitChanges();
    return user;
}

And call it like this:

var user = new User { Password = "123" };
UpdateUser(123, user);

For each field I need to write IF statement and I thinking that I doing something wrong. Also because I am using comparsion with default(string) I cannot set empty values to rows. Please, tell me, what is right way to do this?

PS: Please, sorry for my bad English.

Answer 1

You are misusing LINQ 2 SQL. You shouldn't even have a generic UpdateUser method because you don't need it. If you want to write a certain field of an entity, just do it:

var user = GetUser(userId);
user.Password = "123";

And you're done. When you have made all changes to the object model, call SubmitChanges at the end. It is not necessary to call it after each mutation.

You are using LINQ 2 SQL as a CRUD repository but it is not meant to be one. It is meant to give you a live object model that you can treat like normal C# objects. In the end you synchronize with the database by calling SubmitChanges .

Answer 2

This is possible just with SubmitChanges:

This gets the user:
    var user=context.User.Where(m=>m.id == "xyz").FirstOrDefault();

This updates the above user:
user.Password = "xyz";
context.User.SubmitChanges();

Answer 3

I think you are looking into the wrong way for optimization. An update command on single column isn't much different than on every other column than PK. Your validation logics might take more time to process than your optimized update command.

However if it is always the password that needs to be updated, you can do it this way :

public User ChangePassword(int userId, string password)
{
  var user = new User() { Id = userId };
  _context.Users.Attach(user); 
  user.Password = password;
  _context.SaveChanges();

  return user;
}