SQLite net with linq on Windows Phone 8.1

Question

Suppose I have following table:

public class User
{

    public User()
    { 
    }
    public User(string name, string pass)
    {
        addUser(name, pass);
    }

    public void addUser(string name, string pass)
    {
        //todo cryptography
        this.login = name;
        this.password = pass;
    }


    [PrimaryKey, AutoIncrement]
    public int ID { get; set; }
    [Unique, MaxLength(20)]
    public string login { get; set; }
    [MaxLength(20)]
    private string password { get; set; }
    public string group { get; set; }
}

1. I have unique keyword in login field. If I add another person with same login, exception will be thrown or this insert command will be skiped?

2. What is a best way to get user name from User table? To get all users depending on some name condition I use this example function for my test purpose.

     public async void GetRow(string name) { var query = dbConnection.Table<User>().Where(x => x.login.Contains(name)); var result = await query.ToListAsync(); foreach (var item in result) { User u = item as User; MessageDialog msgbox = new MessageDialog(u.login); await msgbox.ShowAsync(); } } 

Suppose I want to get only 1 record from Users table based on a given name, what would be best way to do that. I tried something like this:

from u in dbConection.Table<User> select u.Login where u.Login = name;

3. How to return from GetRow function described in 2 question user password? I can recieve only list of items, I search on the web and I find FirstOrDefault function but is there any better way to do it?

Edit:

ad 1. Throws exception

ad 2.This works only if record exists in table, in other case throws exception

 var query = (from s in dbConnection.Table<User>() where s.login == name && s.password == password select s).FirstAsync();  
    User qr = query.Result;

Answer 1

I find solution. This is a simple validation function. Thank You for Your help.

            try
            {
                var query = (from s in dbConnection.Table<User>() where s.login == name && s.password == password select s).FirstAsync();
                User x = await query;

                if (x != null) return true;
                else return false;                
            }
            catch (Exception)
            {
                return false;
            }

Answer 2

var some_strings = new List<string> {"Szcz","epan"};
string first_string = some_strings.FirstOrDefault();
//first_string = "szcz";

some_strings = new List<string>();
first_string = some_strings.FirstOrDefault();
//first_string = null;
if (first_string != null)
    // do your stuff here.

if you were dealing with Int 's, then the default would have been zero. IF it's a custom class, it'll be whatever your default for the class is.