已編譯查詢 (LINQ to Entities)

當您的應用程式執行了 Entity Framework 中結構類似的查詢多次時，您可經常增加效能，其方式是編譯查詢一次，然後使用不同的參數執行查詢多次。 例如，應用程式可能必須擷取特定城市中的所有客戶；此城市是使用者在執行階段於表單中所指定。 LINQ to Entities 支援針對這個用途所編譯的查詢。

從 .NET Framework 4.5 開始會自動快取 LINQ 查詢。 不過，之後執行時您仍可以使用已編譯的 LINQ 查詢減少這種成本，且已編譯查詢可能比自動快取的 LINQ 查詢更有效率。 不會自動快取將 Enumerable.Contains 運算子套用至記憶體中集合的 LINQ to Entities 查詢。 此外，也不允許在已編譯的 LINQ 查詢中參數化記憶體中的集合。

CompiledQuery 類別提供查詢的編譯和快取以供重複使用。 就概念而言，這個類別包含數個多載之 CompiledQuery 的 Compile 方法。 呼叫 Compile 方法可建立新委派來代表已編譯的查詢。 Compile 所提供的 ObjectContext 方法和參數值會傳回一個產生某個結果 (例如 IQueryable<T> 執行個體) 的委派。 此查詢只會在第一次執行期間編譯一次。 不過，您之後無法變更在編譯階段中，針對查詢所設定的合併選項。 一旦查詢已編譯之後，您就只能提供基本型別的參數，但是無法取代會變更產生之 SQL 的查詢部分。 如需詳細資訊，請參閱 EF 合併選項和編譯的查詢 (英文)。

CompiledQuery 之 Compile 方法所編譯的 LINQ to Entities 查詢運算式是由其中一個泛型 Func 委派代表，例如 Func<T1,T2,T3,T4,TResult>。 查詢運算式最多只能封裝一個 ObjectContext 參數、一個傳回參數和十六個查詢參數。 如果需要使用十六個以上的查詢參數，您可以建立其屬性代表查詢參數的結構。 然後，當您設定這些參數之後，就可以將此結構的屬性用於查詢運算式中。

範例 1

下列範例會先編譯然後再叫用接受 Decimal 輸入參數的查詢，並且傳回訂單序列，其中的總到期金額大於或等於 $200.00：

static readonly Func<AdventureWorksEntities, Decimal, IQueryable<SalesOrderHeader>> s_compiledQuery2 =
    CompiledQuery.Compile<AdventureWorksEntities, Decimal, IQueryable<SalesOrderHeader>>(
            (ctx, total) => from order in ctx.SalesOrderHeaders
                            where order.TotalDue >= total
                            select order);

static void CompiledQuery2()
{
    using (AdventureWorksEntities context = new AdventureWorksEntities())
    {
        Decimal totalDue = 200.00M;

        IQueryable<SalesOrderHeader> orders = s_compiledQuery2.Invoke(context, totalDue);

        foreach (SalesOrderHeader order in orders)
        {
            Console.WriteLine("ID: {0}  Order date: {1} Total due: {2}",
                order.SalesOrderID,
                order.OrderDate,
                order.TotalDue);
        }
    }
}

ReadOnly s_compQuery2 As Func(Of AdventureWorksEntities, Decimal, IQueryable(Of SalesOrderHeader)) = _
    CompiledQuery.Compile(Of AdventureWorksEntities, Decimal, IQueryable(Of SalesOrderHeader))( _
                Function(ctx As AdventureWorksEntities, total As Decimal) _
                    From order In ctx.SalesOrderHeaders _
                    Where (order.TotalDue >= total) _
                    Select order)

Sub CompiledQuery2()
    Using context As New AdventureWorksEntities()

        Dim totalDue As Decimal = 200.0

        Dim orders As IQueryable(Of SalesOrderHeader) = s_compQuery2.Invoke(context, totalDue)

        For Each order In orders
            Console.WriteLine("ID: {0}  Order date: {1} Total due: {2}", _
                                    order.SalesOrderID, _
                                    order.OrderDate, _
                                    order.TotalDue)
        Next
    End Using
End Sub

範例 2

下列範例會先編譯再叫用傳回 ObjectQuery<T> 執行個體的查詢：

static readonly Func<AdventureWorksEntities, ObjectQuery<SalesOrderHeader>> s_compiledQuery1 =
    CompiledQuery.Compile<AdventureWorksEntities, ObjectQuery<SalesOrderHeader>>(
            ctx => ctx.SalesOrderHeaders);

static void CompiledQuery1_MQ()
{

    using (AdventureWorksEntities context = new AdventureWorksEntities())
    {
        IQueryable<SalesOrderHeader> orders = s_compiledQuery1.Invoke(context);

        foreach (SalesOrderHeader order in orders)
            Console.WriteLine(order.SalesOrderID);
    }
}

ReadOnly s_compQuery1 As Func(Of AdventureWorksEntities, ObjectQuery(Of SalesOrderHeader)) = _
    CompiledQuery.Compile(Of AdventureWorksEntities, ObjectQuery(Of SalesOrderHeader))( _
                Function(ctx) ctx.SalesOrderHeaders)

Sub CompiledQuery1_MQ()

    Using context As New AdventureWorksEntities()

        Dim orders As ObjectQuery(Of SalesOrderHeader) = s_compQuery1.Invoke(context)

        For Each order In orders
            Console.WriteLine(order.SalesOrderID)
        Next

    End Using
End Sub

範例 3

下列範例會先編譯再叫用一個查詢，此查詢會以 Decimal 值形式傳回產品標價的平均值。

static readonly Func<AdventureWorksEntities, Decimal> s_compiledQuery3MQ = CompiledQuery.Compile<AdventureWorksEntities, Decimal>(
            ctx => ctx.Products.Average(product => product.ListPrice));

static void CompiledQuery3_MQ()
{

    using (AdventureWorksEntities context = new AdventureWorksEntities())
    {
        Decimal averageProductPrice = s_compiledQuery3MQ.Invoke(context);

        Console.WriteLine("The average of the product list prices is $: {0}", averageProductPrice);
    }
}

Using context As New AdventureWorksEntities()
    Dim compQuery = CompiledQuery.Compile(Of AdventureWorksEntities, Decimal)( _
            Function(ctx) ctx.Products.Average(Function(Product) Product.ListPrice))

    Dim averageProductPrice As Decimal = compQuery.Invoke(context)

    Console.WriteLine("The average of the product list prices is $: {0}", averageProductPrice)
End Using

範例 4

下列範例會先編譯然後再叫用接受 String 輸入參數的查詢，然後傳回電子郵件地址以指定字串開始的 Contact：

static readonly Func<AdventureWorksEntities, string, Contact> s_compiledQuery4MQ =
    CompiledQuery.Compile<AdventureWorksEntities, string, Contact>(
            (ctx, name) => ctx.Contacts.First(contact => contact.EmailAddress.StartsWith(name)));

static void CompiledQuery4_MQ()
{
    using (AdventureWorksEntities context = new AdventureWorksEntities())
    {
        string contactName = "caroline";
        Contact foundContact = s_compiledQuery4MQ.Invoke(context, contactName);

        Console.WriteLine("An email address starting with 'caroline': {0}",
            foundContact.EmailAddress);
    }
}

Using context As New AdventureWorksEntities()
    Dim compQuery = CompiledQuery.Compile(Of AdventureWorksEntities, String, Contact)( _
            Function(ctx, name) ctx.Contacts.First(Function(contact) contact.EmailAddress.StartsWith(name)))

    Dim contactName As String = "caroline"
    Dim foundContact As Contact = compQuery.Invoke(context, contactName)

    Console.WriteLine("An email address starting with 'caroline': {0}", _
            foundContact.EmailAddress)
End Using

範例 5

下列範例會先編譯然後再叫用接受 DateTime 和 Decimal 輸入參數的查詢，並且傳回訂單序列，其中的訂單日期晚於 2003 年 3 月 8 日，總應付金額則少於 $300.00：

static readonly Func<AdventureWorksEntities, DateTime, Decimal, IQueryable<SalesOrderHeader>> s_compiledQuery5 =
    CompiledQuery.Compile<AdventureWorksEntities, DateTime, Decimal, IQueryable<SalesOrderHeader>>(
            (ctx, orderDate, totalDue) => from product in ctx.SalesOrderHeaders
                                          where product.OrderDate > orderDate
                                             && product.TotalDue < totalDue
                                          orderby product.OrderDate
                                          select product);

static void CompiledQuery5()
{
    using (AdventureWorksEntities context = new AdventureWorksEntities())
    {
        DateTime date = new DateTime(2003, 3, 8);
        Decimal amountDue = 300.00M;

        IQueryable<SalesOrderHeader> orders = s_compiledQuery5.Invoke(context, date, amountDue);

        foreach (SalesOrderHeader order in orders)
        {
            Console.WriteLine("ID: {0} Order date: {1} Total due: {2}", order.SalesOrderID, order.OrderDate, order.TotalDue);
        }
    }
}

ReadOnly s_compQuery5 = _
   CompiledQuery.Compile(Of AdventureWorksEntities, DateTime, Decimal, IQueryable(Of SalesOrderHeader))( _
                Function(ctx, orderDate, totalDue) From product In ctx.SalesOrderHeaders _
                                                   Where product.OrderDate > orderDate _
                                                      And product.TotalDue < totalDue _
                                                   Order By product.OrderDate _
                                                   Select product)
Sub CompiledQuery5()

    Using context As New AdventureWorksEntities()

        Dim orderedAfterDate As DateTime = New DateTime(2003, 3, 8)
        Dim amountDue As Decimal = 300.0

        Dim orders As IQueryable(Of SalesOrderHeader) = _
            s_compQuery5.Invoke(context, orderedAfterDate, amountDue)

        For Each order In orders
            Console.WriteLine("ID: {0} Order date: {1} Total due: {2}", _
                              order.SalesOrderID, order.OrderDate, order.TotalDue)
        Next

    End Using
End Sub

範例 6

下列範例會先編譯然後再叫用接受 DateTime 輸入參數的查詢，並且傳回訂單序列，其中的訂單日期晚於 2004 年 3 月 8 日。 此查詢會傳回匿名型別序列形式的訂單資訊。 匿名型別是由編譯器所推斷，所以您無法在 CompiledQuery 的 Compile 方法中指定型別參數，而且此型別會在查詢本身定義。

using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    var compiledQuery = CompiledQuery.Compile((AdventureWorksEntities ctx, DateTime orderDate) =>
        from order in ctx.SalesOrderHeaders
        where order.OrderDate > orderDate
        select new {order.OrderDate, order.SalesOrderID, order.TotalDue});

    DateTime date = new DateTime(2004, 3, 8);
    var results = compiledQuery.Invoke(context, date);

    foreach (var order in results)
    {
        Console.WriteLine("ID: {0} Order date: {1} Total due: {2}", order.SalesOrderID, order.OrderDate, order.TotalDue);
    }
}

Using context As New AdventureWorksEntities()
    Dim compQuery = CompiledQuery.Compile( _
            Function(ctx As AdventureWorksEntities, orderDate As DateTime) _
                From order In ctx.SalesOrderHeaders _
                Where order.OrderDate > orderDate _
                Select New With {order.OrderDate, order.SalesOrderID, order.TotalDue})

    Dim orderedAfterDate As DateTime = New DateTime(2004, 3, 8)

    Dim orders = compQuery.Invoke(context, orderedAfterDate)

    For Each order In orders
        Console.WriteLine("ID: {0} Order date: {1} Total due: {2}", _
                          order.SalesOrderID, order.OrderDate, order.TotalDue)
    Next

End Using

範例 7

下列範例會先編譯然後再叫用接受使用者定義結構輸入參數的查詢，並且傳回訂單序列。 此結構會定義開始日期、結束日期和應付總額查詢參數，而且此查詢會傳回在 2003 年 3 月 3 日與 3 月 8 日之間出貨而且應付總額超過 $700.00 的訂單。

static Func<AdventureWorksEntities, MyParams, IQueryable<SalesOrderHeader>> s_compiledQuery =
    CompiledQuery.Compile<AdventureWorksEntities, MyParams, IQueryable<SalesOrderHeader>>(
            (ctx, myparams) => from sale in ctx.SalesOrderHeaders
                               where sale.ShipDate > myparams.startDate && sale.ShipDate < myparams.endDate
                               && sale.TotalDue > myparams.totalDue
                               select sale);
static void CompiledQuery7()
{

    using (AdventureWorksEntities context = new AdventureWorksEntities())
    {
        MyParams myParams = new MyParams();
        myParams.startDate = new DateTime(2003, 3, 3);
        myParams.endDate = new DateTime(2003, 3, 8);
        myParams.totalDue = 700.00M;

        IQueryable<SalesOrderHeader> sales = s_compiledQuery.Invoke(context, myParams);

        foreach (SalesOrderHeader sale in sales)
        {
            Console.WriteLine("ID: {0}", sale.SalesOrderID);
            Console.WriteLine("Ship date: {0}", sale.ShipDate);
            Console.WriteLine("Total due: {0}", sale.TotalDue);
        }
    }
}

ReadOnly s_compQuery = CompiledQuery.Compile(Of AdventureWorksEntities, MyParams, IQueryable(Of SalesOrderHeader))( _
                Function(ctx, mySearchParams) _
                    From sale In ctx.SalesOrderHeaders _
                    Where sale.ShipDate > mySearchParams.startDate _
                       And sale.ShipDate < mySearchParams.endDate _
                       And sale.TotalDue > mySearchParams.totalDue _
                    Select sale)

Sub CompiledQuery7()

    Using context As New AdventureWorksEntities()

        Dim myParams As MyParams = New MyParams()
        myParams.startDate = New DateTime(2003, 3, 3)
        myParams.endDate = New DateTime(2003, 3, 8)
        myParams.totalDue = 700.0

        Dim sales = s_compQuery.Invoke(context, myParams)

        For Each sale In sales
            Console.WriteLine("ID: {0}", sale.SalesOrderID)
            Console.WriteLine("Ship date: {0}", sale.ShipDate)
            Console.WriteLine("Total due: {0}", sale.TotalDue)
        Next

    End Using
End Sub

定義查詢參數的結構：

struct MyParams
{
    public DateTime startDate;
    public DateTime endDate;
    public decimal totalDue;
}

Public Structure MyParams
    Public startDate As DateTime
    Public endDate As DateTime
    Public totalDue As Decimal
End Structure

另請參閱

• ADO.NET Entity Framework
• LINQ to Entities
• EF 合併選項與已編譯的查詢