Intersecting two lists using LINQ

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开发者_运维知识库].ClaimID = 965, etc.).

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

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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.

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Since your class doesn't implement IEquatable<SearchItems>, you'll need to use the overload of Intersect which allows for an IEqualityComparer<T>.

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You should implement the GetHashCode and Equals methods on SearchItem, so that two different instances can be compared. (By default, two objects are considered equal if they are references to the same instance)