ObjectQuery<T>.Distinct 方法

定義

將查詢限制為唯一的結果。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)

傳回

ObjectQuery<T>

新的 ObjectQuery<T> 執行個體,它就相當於套用了 SELECT DISTINCT 的原始執行個體。A new ObjectQuery<T> instance that is equivalent to the original instance with SELECT DISTINCT applied.

範例

本主題中的範例是以 Microsoft SQL Server 產品範例: Database為基礎。The example in this topic is based on the Microsoft SQL Server Product Samples: Database. 此範例會使用 UnionAll 方法來建立新的 ObjectQuery<T> 物件。The example uses UnionAll method to create a new ObjectQuery<T> object. 然後,它會針對新的 Distinct 物件呼叫 ObjectQuery<T>,以便取得這個查詢的唯一結果。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

備註

此查詢產生器方法會傳回一個 ObjectQuery<T> 實例,此實例等同于已套用 SELECT DISTINCT 的原始查詢。This query builder method returns an ObjectQuery<T> instance that is equivalent to the original query with SELECT DISTINCT applied.

DISTINCT運算子無法套用至物件,該物件包含資料來源 ((例如 Ntext) )中不可比較資料行的對應。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).

適用於