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。 同時使用下列 Entity Framework 查詢技術顯示相同範例：

• LINQ to Entities

• Entity SQL with ObjectQuery<T>

• Query builder methods of ObjectQuery<T>

本主題的範例根據 Adventure Works Sales Model。若要執行此主題中的程式碼，您必須已經將 Adventure Works Sales Model 加入到專案中，並設定您的專案使用 Entity Framework。如需詳細資訊，請參閱 HOW TO：使用實體資料模型精靈 (Entity Framework) 或 HOW TO：手動設定 Entity Framework 專案及 HOW TO：手動設定 Entity Framework 專案。

範例

以下是 LINQ to Entities 範例。

Using context As New AdventureWorksEntities()
    ' Specify the order amount. 
    Dim orderCost As Integer = 2500

    ' Define a LINQ query that returns only online orders 
    ' more than the specified amount. 
    Dim onlineOrders = From order In context.SalesOrderHeaders _
        Where order.OnlineOrderFlag = True AndAlso order.TotalDue > orderCost _
        Select order

    ' Print order information. 
    For Each onlineOrder In onlineOrders
        Console.WriteLine("Order ID: {0} Order date: ", onlineOrder.SalesOrderID)
        Console.WriteLine("Order date: {0:d}", onlineOrder.OrderDate)
        Console.WriteLine("Order number: {0}", onlineOrder.SalesOrderNumber)
    Next
End Using

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

    // Define a LINQ query that returns only online orders
    // more than the specified amount.
    var onlineOrders =
        from order in context.SalesOrderHeaders
        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);
    }
}

以下是 Entity SQL 範例。

Using context As New AdventureWorksEntities()
    ' Specify the order amount. 
    Dim orderCost As Decimal = 2500

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

    ' Define an ObjectQuery and pass the maxOrderCost parameter. 
    Dim onlineOrders As 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
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 AdventureWorksEntities.SalesOrderHeaders AS o 
        WHERE o.OnlineOrderFlag = TRUE AND o.TotalDue > @ordercost";

    // 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);
    }
}

以下是查詢產生器方法範例。

Using context As New AdventureWorksEntities()
    ' Specify the order amount. 
    Dim orderCost As Integer = 2500

    ' Define an ObjectQuery that returns only online orders 
    ' more than the specified amount. 
    Dim onlineOrders As ObjectQuery(Of SalesOrderHeader) = _
        context.SalesOrderHeaders.Where("it.OnlineOrderFlag = TRUE AND 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
End Using

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

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