/// <summary>
/// verify if the employer has active contracts, if it is true, we can not delete him
/// </summary>
/// <param name="oldEmployer"></param>
public void DelEmployer(Employer oldEmployer)
{
IEnumerable <Contract> verification = from contract in dal.ReturnContracts()
where contract.employerId == oldEmployer.id && contract.hasBeenSigned
select contract;
if (verification.Any(contract => contract.endWork < DateTime.Now))
{
throw new Exception("we can not delete employer because he has active contracts");
}
dal.DelEmployer(oldEmployer);
}