Why does the compiler swear at the method in the delegate passed to FirstOrDefault?

Question

C++ / C#

Call

user = db.Users.FirstOrDefault(u => u.Login == loginTextBox.Text && u.PasswordHash == GetMD5Hash(passwordTextBox.Text));

Method

public static string GetMD5Hash(string str)
{            
    MD5 md5 = MD5.Create();
    byte[] hash = md5.ComputeHash(Encoding.UTF8.GetBytes(str));
    StringBuilder stringBuilder = new StringBuilder();
    for (int i = 0; i < hash.Length; i++)
    {
        stringBuilder.Append(hash[i].ToString("x2"));
    }
    return stringBuilder.ToString();
}

Mistake:

Answer 1

In this case, LINQ is trying to convert a LINQ query into a server-side SQL query, and a method such as GetMD5Hash does not exist for it, so it throws an error. When converting, it does not first execute the GetMD5Hash method, with a continuation, but immediately tries to get the SQL code. Therefore, in this case, it can simply be taken out.