Throwing exception if lambda expression fails

Question

To simplify, let's say I have a method that should return a User object from an ID found in a list of users. If no user is found I want to throw an Exception.

My current code works:

public User GetUserFromID(int id)
{
    foreach (User u in Users)
        if (u.id == id)
            return u;
    
    throw new Exception("No user is found");
}

But my problem comes when I want to find a user with a lambda expression instead of the foreach loop. The following code succeeds in returning the correct User object but never throws an exception if nothing is found.

public User GetUserFromID(int id)
{
    return Users.Find(u => u.id == id);
    
    throw new Exception("No user is found");
}

MarredCheese · Accepted Answer · 2021-08-21 04:13:35Z

1

You could use User.Single(...) which would throw an exception if there isn't exactly one match:

public User GetUserFromID(int id)
{
    return Users.Single(u => u.id == id);
}

Just for completeness, if you wanted to throw your own exception, then you could do something like this.

Using SingleOrDefault will return null if there is no match or if there is more than 1 match, so you can check for null to determine if an exception should be thrown:

public User GetUserFromID(int id)
{
    var user = Users.SingleOrDefault(u => u.id == id);

    if(user == null)
        throw new Exception("No user is found");
 
    return user;
}

edited Aug 21, 2021 at 4:13

MarredCheese

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answered Jan 17, 2017 at 9:14

musefan

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Comments

MarredCheese · Accepted Answer · 2021-08-21 04:10:44Z

0

public User GetUserFromID(int id)
{
    return Users.Single(u => u.id == id);
}

Users.Single will throw an exception when there is not exactly one match.

edited Aug 21, 2021 at 4:10

MarredCheese

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answered Jan 17, 2017 at 9:15

madoxdev

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