Question

We have the following code to check if the given username and password exists in database:

    public User GetUserByUserNameAndPassword(string userName, string userPassword)
    {
        using (var context = DataObjectFactory.CreateContext())
        {
            return Mapper.Map(context.UserEntities.Single(u => u.UserName == userName && u.UserPassword == userPassword));
        }
    }

If we have the username and password in database this works fine but throws an error if username or password is wrong and no records found.

This might be simple but as I am new to lambda could not get get it right.

How can I change the lambda query so we can handle nulls?

Thanks

Answer 1

Use SingleOrDefault, which will return only one record or null if none exists.

return Mapper.Map(context.UserEntities.SingleOrDefault(u => u.UserName == userName && u.UserPassword == userPassword));

Later you can check:

User returnedObject = GetUserByUserNameAndPassword(username,password)

if(returnedObject == null)
{
//User doesn't exist
}

Remember Single/SingleOrDefault will throw an exception if multiple records exist against the criteria.