getting all email address that does not exists in another list

Question

I have two List of objects like this:

List<EmployeeInfo> emp = getEmployees();
List<EmailList> emailist = getMasterList();

I want to get all the employees email address, firstname, lastName that exists in emailList, but do not exists in emp list. In other words, I want to exclude the email address of the users that exists in emp list. I wrote below LINQ to achieve this:

  List<EmployeeInfo> result = emp
                     .Where(w => !emailist.Contains(w.EmailAddress))
                        .ToList();

above keeps giving me an error saying "cannot convert from string to emailList.

This is the model for both employeeInfo and emailList

public partial class EmployeeInfo
{
    public int EmployeeInfoId { get; set; }
    public DateTime DateFormFilled { get; set; }
    public string EmployeeNumber { get; set; } = null!;
    public string LastName { get; set; } = null!;
    public string FirstName { get; set; } = null!;
    public string? MiddleName { get; set; }
    public string EmailAddress { get; set; } = null!;
}
public partial class EmailList {
public string? LastName { get; set; }
public string? FirstName { get; set; }
public string? Eid { get; set; }
public string? Email { get; set; }
public DateTime LoadDate { get; set; }
}

any help will be appreciated.

Answer 1

as suggested you use the Any() instead of Contains(). Now this will be a nested loop and pretty slow if the lists are large - O(n^2). convert the knockout list to a hash set and its linear O(1):

var emailHash = new HashSet<string>(emailList.Select(r => r.EmailAddress));
List<Employee> result = emp
    .Where(r => !emailHash.Contains(r.EmailAddress))
    .ToList();

Answer 2

Please try the following:

List<Employee> result = emp
    .Where(w => emailist.FirstOrDefault(m => m.Email == w.EmailAddress) == null)
    .ToList();