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c#listiequalitycomparer

List.Contains is not working as hoped

If I have an object of type MyBull and a List<MyBull> orig:

// Just an example
MyBull x = getMeTheObjectWithIdFromDB(9);

orig.add(x);

// Again same? data object
MyBull y = getMeTheObjectWithIdFromDB(9);

Why is this false then?

// This is false, even though all the properties
// of x and y are the same.
orig.Contains<MyBull>(y);
Solution

  • By default objects will expose reference based equality. If you want custom rules, such as equality based on id fields, you need to override the Equals and GetHashCode methods.