ObjectQuery<T>.Distinct Method

Definition

Schränkt die Abfrage auf eindeutige Ergebnisse ein.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

ObjectQuery<T>

Eine neue ObjectQuery<T>-Instanz, die der ursprünglichen Instanz entspricht, für die jedoch SELECT DISTINCT festgelegt ist.A new ObjectQuery<T> instance that is equivalent to the original instance with SELECT DISTINCT applied.

Examples

Das Beispiel in diesem Thema basiert auf den Microsoft SQL Server Product Samples: Database.The example in this topic is based on the Microsoft SQL Server Product Samples: Database. In dem Beispiel wird die UnionAll-Methode zur Erstellung eines neuen ObjectQuery<T>-Objekts verwendet.The example uses UnionAll method to create a new ObjectQuery<T> object. Anschließend wird Distinct für das neue ObjectQuery<T>-Objekt aufgerufen, um die eindeutigen Ergebnisse dieser Abfrage abzurufen.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

Diese Abfrage-Generator-Methode gibt eine ObjectQuery<T>-Instanz zurück, die der ursprünglichen Abfrage entspricht, bei der SELECT-unter schiedliche verwendet werden.This query builder method returns an ObjectQuery<T> instance that is equivalent to the original query with SELECT DISTINCT applied.

Der DISTINCT-Operator kann nicht auf ein Objekt angewendet werden, das eine Zuordnung zu einer nicht vergleichbaren Spalte in der Datenquelle (z. b. ntext) einschließt.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