ObjectQuery<T>.Distinct 方法

定义

命名空间:

System.Data.Objects

程序集:

System.Data.Entity.dll

将查询限制为唯一结果。

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)

返回

ObjectQuery<T>

一个新的 ObjectQuery<T> 实例，等效于应用了 SELECT DISTINCT 的原始实例。

示例

此示例使用 UnionAll 方法创建新 ObjectQuery<T> 对象。 然后对新的 Distinct 对象调用 ObjectQuery<T>，以获取此查询的唯一结果。

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);
}

注解

此查询生成器方法返回一个 ObjectQuery<T> 实例，该实例等效于应用 了 SELECT DISTINCT 的原始查询。

运算符 DISTINCT 不能应用于包含到数据源 (中非可比列的映射的对象，例如 ntext) 。

另请参阅

• 以对象形式查询数据（实体框架）