LINQ Check exist Username then get that User's ID

Question

I have an Account table:

    table Account
    (
    UserId int identity(1, 1),
    UserName nvarchar(20) not null unique,
    Password nvarchar(20) not null
    )

By using LINQ. Whether I can check exist UserName for an account then. And it's true then get UserId for that account (I'm use ASP MVC 4 with Entity Framework)

score 3 · Answer 1 · answered Apr 01 '14 at 15:57

3

var user = Context.Accounts.SinlgeOrDefault(user => user.UserName=="yourValue");
if(user!=null)
{
// you can safely access the user properties here
}

answered Apr 01 '14 at 15:57

Massimiliano Peluso

26,379
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Andre Figueiredo · Accepted Answer · 2014-04-01T16:08:30.867

3

When using Linq to query from DB, I prefer to use query expression, that is closer to SQL notation than Lambda notation.

Given that you have the username:

try {
    int userId = (from x in context.Account
                   where x.UserName == username
                   select x.UserId).SingleOrDefault());

    if (userId > 0){
        // user exists
    }
    else {
        // user does not exist
    }
}
catch(InvalidOperationException ex){
    // has more than one element
}

edited Apr 01 '14 at 16:08

answered Apr 01 '14 at 15:57

Andre Figueiredo

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Edit: Much better. :) – JC Ford Apr 01 '14 at 15:59
1

Wait. Actually no it will still return 0. So userId will have a value. – JC Ford Apr 01 '14 at 16:02
yes, I've updated this. "OrDefault()" means that will return `default(TSource)` and not `default(TDestiny)` :) – Andre Figueiredo Apr 01 '14 at 16:05
1

Yeah. You could maybe project the UserId into a nullable int inside the query, in which case SingleOrDefault() might then return a nullable with no value. Haven't tested this though. – JC Ford Apr 01 '14 at 16:07
yes, that's why I've declared userId as `int?` before, but I think that could be better to use same type for `userId` and `x.UserId` – Andre Figueiredo Apr 01 '14 at 16:10
Dry coding here, but would this work? `int? userId = (from x in context.Account where x.UserName == username select new Nullable(x.UserId)).SingleOrDefault());` – JC Ford Apr 01 '14 at 16:13
Won't because this `new int?(x.CodPreco)` is not supported in Linq. – Andre Figueiredo Apr 01 '14 at 16:21
int? and Nullable are the same thing. Or rather int? is just shorthand for Nullable. – JC Ford Apr 01 '14 at 16:23
1

It works okay, too! It maybe better ideas in some cases for `trycatch` that it return more than one element. I thank you too for the anwser – haind Apr 01 '14 at 16:30
@JC. [int? is same thing that Nullable](http://stackoverflow.com/questions/4028830) – Andre Figueiredo Apr 01 '14 at 16:31
What I mean is that `int?` and `Nullable` are the same thing indeed. But Linq does not **support** `int?` constructor. – Andre Figueiredo Jul 14 '15 at 18:53

LINQ Check exist Username then get that User's ID

2 Answers2