Question

I have the following class called SearchItem, which extends another class called Claim. For brevity, I’m simply including the class names and their properties.

public class SearchItem : Claim {

    public int FileStreamID { get; set; }
    public Int16 UploadedByLabID { get; set; }
    public string FileName { get; set; }
    public string TypeDesc { get; set; }
    public string UploadedByLab { get; set; }
    public string UploadedByUser { get; set; }
    public DateTime? UploadDate { get; set; }

}

public class Claim {

    public int ClaimID { get; set; }
    public string DOB_Format {
        get {
            string s = "";
            if (this.DOB.HasValue)
                s = this.DOB.Value.ToString("MM/dd/yyyy");
            return s;
        }
    }
    public string FirstName { get; set; }
    public string FullClaimDesc {
        get {
            return this.FullName + " (" + this.SSN_Mask + ")";
        }
    }
    public string FullName {
        get {
            string s = this.LastName + ", " + this.FirstName;
            if (!string.IsNullOrEmpty(this.MiddleName))
                s += " " + this.MiddleName;
            return s;
        }
    }
    public string LastName { get; set; }
    public string MiddleName { get; set; }
    public string SSN { get; set; }
    public string SSN_Mask {
        get {
            string s = "";
            if (this.SSN.Length > 0)
                s = Claim.FormatHyphens(this.SSN);
            return s;
        }
    }
    public string Suffix { get; set; }
    public DateTime? DOB { get; set; }
    public DateTime? RequestDate { get; set; }
    public Int16 OwnedByLabID { get; set; }
    public List<Int16> lstLabRecipientID { get; set; }
}

I have two lists that contains n SearchItems.

List<SearchItems> lstMain = new List<SearchItems>();
List<SearchItems> lstTemp = new List<SearchItems>();

Assume that lstMain contains 25 SearchItems and lstTemp contains 5 SearchItems. What I would like to do is use Intersect in order to retrieve the SearchItems that are the same between lstMain and lstTemp.

IEnumerable<SearchItem> results = lstMain.Intersect(lstTemp);

However, results always comes up empty. I am certain that the two lists contains 3 SearchItems that are identical, and by identical I mean that their properties yield the same values (ie – lstMain[2].ClaimID = 965 and lstTemp[0].ClaimID = 965, etc.).

So am I expecting too much out of the Intersect extension method? Can it not handle complext types that implement inheritance?

Answer 1

Since I assume the class instances for the items that are considered “the same” are different in both lists you need a custom IEqualityComparer<SearchItem> to use Intersect(), you can pass it as a second parameter.

In your implementation of IEqualityComparer<SearchItem> you would then have to compare the properties of two SearchItem instances to determine if they should be considered equal, an example can be found here.