ObjectQuery<T>.Distinct ObjectQuery<T>.Distinct ObjectQuery<T>.Distinct ObjectQuery<T>.Distinct Method

Definition

Limits the query to unique results.

public:
 System::Data::Objects::ObjectQuery<T> ^ Distinct();
public System.Data.Objects.ObjectQuery<T> Distinct ();
member this.Distinct : unit -> System.Data.Objects.ObjectQuery<'T>
Public Function Distinct () As ObjectQuery(Of T)

Returns

A new ObjectQuery<T> instance that is equivalent to the original instance with SELECT DISTINCT applied.

Examples

The example in this topic is based on the AdventureWorks Sales Model. The example uses UnionAll method to create a new ObjectQuery<T> object. Then it calls Distinct on the new ObjectQuery<T> object to get the unique results of this query.

int productID = 100;
using (AdventureWorksEntities context =
    new AdventureWorksEntities())
{
    string queryString =
        @"SELECT VALUE product FROM AdventureWorksEntities.Products 
            AS product WHERE product.ProductID < @productID";

    ObjectQuery<Product> productQuery =
        new ObjectQuery<Product>(queryString,
            context, MergeOption.NoTracking);

    ObjectQuery<Product> productQuery2 =
        new ObjectQuery<Product>(queryString,
            context, MergeOption.NoTracking);

    ObjectQuery<Product> productQuery3 =
        productQuery.UnionAll(productQuery2);

    productQuery3.Parameters.Add(new ObjectParameter("productID", productID));

    Console.WriteLine("Result of UnionAll");
    Console.WriteLine("------------------");

    // Iterate through the collection of Product items, 
    // after the UnionAll method was called on two queries.
    foreach (Product result in productQuery3)
    {
        Console.WriteLine("Product Name: {0}", result.ProductID);
    }
    ObjectQuery<Product> productQuery4 = productQuery3.Distinct();

    Console.WriteLine("\nResult of Distinct");
    Console.WriteLine("------------------");

    // Iterate through the collection of Product items.
    // after the Distinct method was called on a query. 
    foreach (Product result in productQuery4)
        Console.WriteLine("Product Name: {0}", result.ProductID);
}
Dim productID = 100
Using context As New AdventureWorksEntities()
    Dim queryString As String = "SELECT VALUE product FROM AdventureWorksEntities.Products " & _
            " AS product WHERE product.ProductID < @productID"

    Dim productQuery As New ObjectQuery(Of Product)(queryString, context, MergeOption.NoTracking)

    Dim productQuery2 As New ObjectQuery(Of Product)(queryString, context, MergeOption.NoTracking)

    Dim productQuery3 As ObjectQuery(Of Product) = productQuery.UnionAll(productQuery2)

    productQuery3.Parameters.Add(New ObjectParameter("productID", productID))

    Console.WriteLine("Result of UnionAll")
    Console.WriteLine("------------------")

    ' Iterate through the collection of Product items, 
    ' after the UnionAll method was called on two queries. 
    For Each result As Product In productQuery3
        Console.WriteLine("Product Name: {0}", result.ProductID)
    Next
    Dim productQuery4 As ObjectQuery(Of Product) = productQuery3.Distinct()

    Console.WriteLine(vbLf & "Result of Distinct")
    Console.WriteLine("------------------")

    ' Iterate through the collection of Product items. 
    ' after the Distinct method was called on a query. 
    For Each result As Product In productQuery4
        Console.WriteLine("Product Name: {0}", result.ProductID)
    Next
End Using

Remarks

This query builder method returns an ObjectQuery<T> instance that is equivalent to the original query with SELECT DISTINCT applied.

The DISTINCT operator cannot be applied to an object that includes a mapping to a non-comparable column in the data source (such as ntext).

Applies to

See also