ObjectQuery<T>.Distinct Method ()

 
System_CAPS_noteNote

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Limits the query to unique results.

Namespace:   System.Data.Objects
Assembly:  System.Data.Entity (in System.Data.Entity.dll)

public ObjectQuery<T> Distinct()

Return Value

Type: System.Data.Objects.ObjectQuery<T>

A new ObjectQuery<T> instance that is equivalent to the original instance with SELECT DISTINCT applied.

This query builder method returns an ObjectQuery<T> instance that is equivalent to the original query with SELECT DISTINCT applied.

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).

The example in this topic is based on the AdventureWorks Sales Model. The example uses UnionAll method to create a new ObjectQuery<T> object. 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);
}

.NET Framework
Available since 3.5
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