Question

Supposse, I have a class:

public class PersonalInfo
{
   public string Firsname {get;set;}
   public string Lastname {get;set;}
   public string Email {get;set;}
   public string Phone {get;set;}
}

The data come from file.
And, I need to select data from file by this property:

private IList<PersonalInfo> FindByPersonalData(string firstName, string lastName, string email, string phone)
{
...
}

Several properties can be empty, but if they filled then search by them. I can check every combination, but it’s ugly. What is the best solution?
Thanks

Answer 1

A typical sub-query would be to use a short-circuit on each field. Making some assumptions about your data structures, that could look something like this:

var result = from p in PersonalInfoList
         where (string.IsNullOrEmpty(firstName) || firstName == p.FirstName)
            && (string.IsNullOrEmpty(lastName) || lastName == p.LastName)
            && (string.IsNullOrEmpty(email) || email == p.Email)
            && (string.IsNullOrEmpty(phone) || phone == p.Phone)
         select p

Or, depending on your Linq preference:

var result = PersonalInfoList.Where(p =>
            (string.IsNullOrEmpty(firstName) || firstName == p.FirstName)
            && (string.IsNullOrEmpty(lastName) || lastName == p.LastName)
            && (string.IsNullOrEmpty(email) || email == p.Email)
            && (string.IsNullOrEmpty(phone) || phone == p.Phone))

So, if any parameter is null/empty, the comparison with the data will be skipped.