ObjectQuery<T>.Distinct 方法

定義

命名空間:

System.Data.Objects

組件:

System.Data.Entity.dll

將查詢限制為唯一的結果。

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>

一個與原始實例相同的新 ObjectQuery<T> 實例，並套用了 SELECT DISTINCT 。

範例

這個範例使用 UnionAll 方法來建立一個新 ObjectQuery<T> 物件。 接著它呼叫 Distinct 新 ObjectQuery<T> 物件，取得該查詢的唯一結果。

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);
}

備註

此查詢建構方法回傳 ObjectQuery<T> 一個與原始查詢（ SELECT DISTINCT 套用後）等價的實例。

DISTINCT此運算子無法套用於包含與資料來源中不可比較欄位對應的物件（如 ntext ）。

另請參閱

• 以物件形式查詢資料（實體框架）