HOW TO：篩選資料 (Entity Framework)

本主題將說明如何篩選查詢結果。此範例會傳回代表 $2,500 以上之所有線上訂單的 SalesOrderHeader 物件集合。此外，也會顯示使用下列 實體架構 查詢技術的相同範例：

• LINQ to Entities

• 使用 ObjectQuery<T> 的 Entity SQL

• ObjectQuery<T> 的查詢產生器方法

本主題的範例是根據 Adventure Works Sales Model。若要執行此範例中的程式碼，您必須已經將 AdventureWorks Sales Model 加入到專案中，並設定您的專案使用 實體架構。若要這樣做，請完成 HOW TO：手動設定 Entity Framework 專案和 HOW TO：以手動方式定義 Entity Data Model (Entity Framework) 中的程序。您也可以使用 [Entity Data Model 精靈] 來定義 AdventureWorks Sales Model。如需詳細資訊，請參閱 HOW TO：使用 Entity Data Model 精靈 (Entity Framework)。

範例

以下是 LINQ 到實體 範例。

Using context As AdventureWorksEntities = _
New AdventureWorksEntities()

    ' Specify the order amount.
    Dim orderCost As Integer = 2500

    Try
        ' Define a LINQ query that returns only online orders
        ' more than the specified amount.
        Dim onlineOrders = _
        From order As SalesOrderHeader In context.SalesOrderHeader() _
            Where order.OnlineOrderFlag = True And _
            order.TotalDue > orderCost _
            Select order

        ' Print order information.
        For Each onlineOrder In onlineOrders

            Console.WriteLine("Order ID:{0}Order date: " _
                + "{1}:d Order number: {2}", _
                onlineOrder.SalesOrderID, _
                onlineOrder.OrderDate, _
                onlineOrder.SalesOrderNumber)
        Next
    Catch ex As EntitySqlException
        Console.WriteLine(ex.ToString())
    End Try
End Using

using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    // Specify the order amount.
    int orderCost = 2500;

    try
    {
        // Define a LINQ query that returns only online orders
        // more than the specified amount.
        var onlineOrders =
            from order in context.SalesOrderHeader
            where order.OnlineOrderFlag == true &&
            order.TotalDue > orderCost
            select order;

        // Print order information.
        foreach (var onlineOrder in onlineOrders)
        {
            Console.WriteLine("Order ID: {0} Order date: "
                + "{1:d} Order number: {2}",
                onlineOrder.SalesOrderID,
                onlineOrder.OrderDate,
                onlineOrder.SalesOrderNumber);
        }
    }
    catch (EntitySqlException ex)
    {
        Console.WriteLine(ex.ToString());
    }
}

以下是 實體 SQL 範例。

Using context As AdventureWorksEntities = _
New AdventureWorksEntities()

    ' Specify the order amount.
    Dim orderCost As Integer = 2500

    ' Specify the Entity SQL query that returns only online orders
    ' more than the specified amount.
    Dim queryString As String = "SELECT VALUE o FROM SalesOrderHeader AS o " _
    + "WHERE o.OnlineOrderFlag = TRUE AND o.TotalDue > @ordercost"

    Try
        ' Define an ObjectQuery and pass the maxOrderCost parameter.
        Dim onlineOrders As ObjectQuery(Of SalesOrderHeader) = _
            New ObjectQuery(Of SalesOrderHeader)(queryString, context)
        onlineOrders.Parameters.Add( _
            New ObjectParameter("ordercost", orderCost))

        ' Print order information.
        For Each onlineOrder In onlineOrders
            Console.WriteLine("Order ID:{0}Order date: " _
                + "{1}:d Order number: {2}", _
                onlineOrder.SalesOrderID, _
                onlineOrder.OrderDate, _
                onlineOrder.SalesOrderNumber)
        Next
    Catch ex As EntitySqlException
        Console.WriteLine(ex.ToString())
    End Try
End Using

using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    // Specify the order amount.
    decimal orderCost = 2500;

    // Specify the Entity SQL query that returns only online orders
    // more than the specified amount.
    string queryString = @"SELECT VALUE o FROM SalesOrderHeader AS o 
        WHERE o.OnlineOrderFlag = TRUE AND o.TotalDue > @ordercost";

    try
    {
        // Define an ObjectQuery and pass the maxOrderCost parameter.
        ObjectQuery<SalesOrderHeader> onlineOrders =
            new ObjectQuery<SalesOrderHeader>(queryString, context);
        onlineOrders.Parameters.Add(
            new ObjectParameter("ordercost", orderCost));

        // Print order information.
        foreach (var onlineOrder in onlineOrders)
        {
            Console.WriteLine("Order ID: {0} Order date: "
                + "{1:d} Order number: {2}",
                onlineOrder.SalesOrderID,
                onlineOrder.OrderDate,
                onlineOrder.SalesOrderNumber);
        }
    }
    catch (EntitySqlException ex)
    {
        Console.WriteLine(ex.ToString());
    }
}

以下是查詢產生器方法範例。

Using context As AdventureWorksEntities = _
New AdventureWorksEntities()

    ' Specify the order amount.
    Dim orderCost As Integer = 2500

    Try

        ' Define an ObjectQuery that returns only online orders 
        ' more than the specified amount.
        Dim onlineOrders As ObjectQuery(Of SalesOrderHeader) = _
        context.SalesOrderHeader.Where("it.OnlineOrderFlag = TRUE") _
            .Where("it.TotalDue > @ordercost", _
            New ObjectParameter("ordercost", orderCost))

        ' Print order information.
        For Each onlineOrder In onlineOrders
            Console.WriteLine("Order ID:{0}Order date: " _
                + "{1}:d Order number: {2}", _
                onlineOrder.SalesOrderID, _
                onlineOrder.OrderDate, _
                onlineOrder.SalesOrderNumber)
        Next
    Catch ex As EntitySqlException
        Console.WriteLine(ex.ToString())
    End Try
End Using

using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    // Specify the order amount.
    int orderCost = 2500;

   try
    {
        // Define an ObjectQuery that returns only online orders 
        // more than the specified amount.
        ObjectQuery<SalesOrderHeader> onlineOrders =
            context.SalesOrderHeader
            .Where("it.OnlineOrderFlag = TRUE AND it.TotalDue > @ordercost",
            new ObjectParameter("ordercost", orderCost));

        // Print order information.
        foreach (var onlineOrder in onlineOrders)
        {
            var items = (from item in context.SalesOrderDetail
                        where item.SalesOrderHeader == onlineOrder
                        select item).Take(3);
             Console.WriteLine("Order ID: {0} Order date: "
                + "{1:d} Order number: {2}",
                onlineOrder.SalesOrderID,
                onlineOrder.OrderDate,
                onlineOrder.SalesOrderNumber);
        }
    }
    catch (EntitySqlException ex)
    {
        Console.WriteLine(ex.ToString());
    }
}

另請參閱

其他資源

查詢 Entity Data Model (Entity Framework 工作)