Merge into statement and Entity Framework

Question

I have a Merge stored proc. I mapped the proc to my entity for both insert and update. When I run I get the following error - Any Ideas?

Schema specified is not valid. Errors: Model1.msl(23,14): error 2038: The parameter DataField is bound multiple times.

The Proc:

ALTER PROCEDURE [dbo].[USP_UPSERT_SimpleTableExample]
(
    @NaturalKey1 nchar(10),
    @NaturalKey2 nchar(10),
    @NaturalKey3 nchar(10),
    @DataField nchar(10)
 )

AS
BEGIN
    -- Start Transaction
    BEGIN TRAN

    MERGE INTO dbo.SimpleTableExample ChangeSet
    USING (SELECT   @NaturalKey1 as key1,
                    @NaturalKey2 as key2,
                    @NaturalKey3 as key3) CurrentSet
    ON  ChangeSet.NaturalKey1 = CurrentSet.key1 AND
        ChangeSet.NaturalKey2 = CurrentSet.key2 AND
        ChangeSet.NaturalKey3 = CurrentSet.key3     
    WHEN MATCHED THEN 
        UPDATE SET DataField = @DataField

    WHEN NOT MATCHED 
        THEN INSERT VALUES
           (@NaturalKey1,
           @NaturalKey2,
           @NaturalKey3,
           @DataField) 

    OUTPUT INSERTED.SurrogateKey;

    COMMIT TRAN        

END

And My test code;

static void Main(string[] args)
{
    Class1 c1 = new Class1();

    var test = new SimpleTableExample();
    test.DataField = "data1";
    test.NaturalKey1 = "1";
    test.NaturalKey2 = "2";
    test.NaturalKey3 = "3";

    c1.test(test);
}

public string test(SimpleTableExample ste)
{

    ExamplesEntities1 ex1 = new ExamplesEntities1();

    ex1.AddToSimpleTableExamples(ste);
    ex1.SaveChanges();

    Console.WriteLine("SurrogateKey:0", ste.SurrogateKey);
    Console.WriteLine("EntityKey:0", ste.EntityKey);
    return ste.EntityKey.ToString();
}

Answer 1

Problem solved. The error was added because I mapped the Upsert proc to the table two times, once as the insert and once as the update. This was wrong!

I removed the table mapping to the stored proc.

I changed the stored proc to instead of returning the surogate key to return the entire dataset of what was inserted or updated, which includes the surrogate key.

Next I added function import to the storedproc and had it return a collection so my table.

Then I changed the poc code to take the results of the collection and return the first surrogatekey;

public string test(SimpleTableExample ste)
        {

            ExamplesEntities1 ex1 = new ExamplesEntities1();
            var results = ex1.USP_UPSERT_SimpleTableExample(ste.NaturalKey1, ste.NaturalKey2, ste.NaturalKey3, ste.DataField).ToList<SimpleTableExample>();
            string returnvalue = results.First().SurrogateKey.ToString();
            return returnvalue;
        }

A Test did an insert when there was no matching naturalkeys and an update when natural keys matched.