LINQ query with Distinct and Union

Question

I currently have 2 queries that are returning lists of MyModel like this:

var q1 = ....
         select new MyModel()
         {
             TheData1 = ...
         


        

Answer 1

I think frenchie wants a list of MyModel back instead of just the TheUniqueID.

You need to create a MyModelTheUniqueIDComparer class and pass a new instance of it as a second argument into Union:

class MyModelTheUniqueIDComparer : IEqualityComparer
{
    public bool Equals(MyModel x, MyModel y)
    {
        return x.TheUniqueID == y.TheUniqueID;
    }

    // If Equals() returns true for a pair of objects 
    // then GetHashCode() must return the same value for these objects.

    public int GetHashCode(MyModel myModel)
    {
        return myModel.TheUniqueID.GetHashCode();
    }
}

Then you can call to get the result:

var result = q1.Union(q2, new MyModelTheUniqueIDComparer());

See http://msdn.microsoft.com/en-us/library/bb358407.aspx for a more details.

Update:

Try this:

public class A
{
    public string TheData1 { get; set; }
    public string TheData2 { get; set; }
    public string UniqueID { get; set; }
}

public class AComparer : IEqualityComparer
{

    #region IEqualityComparer Members

    public bool Equals(A x, A y)
    {
        return x.UniqueID == y.UniqueID;
    }

    public int GetHashCode(A obj)
    {
        return obj.UniqueID.GetHashCode();
    }

    #endregion
}

And test with this:

var listOfA = new List();
var q1 = from a in listOfA
                 select new A()
             {
                 TheData1 = "TestData",
                 TheData2 = "TestData",
                 UniqueID = a.UniqueID
             };

var anotherListOfA = new List();
var q2 = from a in anotherListOfA
                 select new A()
                 {
                     TheData1 = "TestData",
                     TheData2 = "TestData",
                     UniqueID = a.UniqueID
                 };

q1.Union(q2, new AComparer());

Make sure you have using System.Linq;