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();

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。

範例

這個範例會使用 UnionAll 方法來建立新的 ObjectQuery<T> 物件。 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。

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

這個查詢產生器方法會傳 ObjectQuery<T> 回實例，這個實例相當於套用 SELECT DISTINCT 的原始查詢。

DISTINCT運算子無法套用至物件，該物件包含數據源中非可比較數據行的對應 (，例如 ntext) 。

適用於

另請參閱

• 以物件形式查詢資料 (Entity Framework)