如何：执行参数化查询（实体框架）

项目
08/22/2008

本主题说明如何使用 ObjectQuery 执行具有参数的 Entity SQL 查询。本示例将两个参数传递到 ObjectQuery，执行查询，并循环访问 Contact 项的集合。将使用以下每种实体框架查询技术演示同一示例：

Entity SQL with ObjectQuery<T>
ObjectQuery <T> 的查询生成器方法

本主题中的示例基于 AdventureWorks 销售模型 (EDM)。若要运行本示例中的代码，必须已将 AdventureWorks 销售模型添加到您的项目中，并将项目配置为使用实体框架。为此，请完成如何：手动配置实体框架项目和如何：手动定义实体数据模型（实体框架）中的过程。也可以使用实体数据模型向导定义 AdventureWorks 销售模型。有关更多信息，请参见如何：使用实体数据模型向导（实体框架）。

示例

以下是 Entity SQL 示例。

Using advWorksContext As New AdventureWorksEntities
    Try
        ' Create a query that takes two parameters.
        Dim queryString As String = "SELECT VALUE Contact FROM AdventureWorksEntities.Contact " & _
            "AS Contact WHERE Contact.LastName = @ln AND " & _
            "Contact.FirstName = @fn"

        ' Add parameters to the collection.
        Dim contactQuery As New ObjectQuery(Of Contact)(queryString, advWorksContext, MergeOption.NoTracking)
        contactQuery.Parameters.Add(New ObjectParameter("ln", "Adams"))
        contactQuery.Parameters.Add(New ObjectParameter("fn", "Frances"))

        ' Iterate through the collection of Contact items.
        For Each result As Contact In contactQuery
            Console.WriteLine("Last Name: {0} First Name: {1}", _
            result.LastName, result.FirstName)
        Next

    Catch ex As EntityException
        Console.WriteLine(ex.ToString)
    Catch ex As InvalidOperationException
        Console.WriteLine(ex.ToString())
    End Try
End Using

using (AdventureWorksEntities advWorksContext =
    new AdventureWorksEntities())
{
    try
    {
        // Create a query that takes two parameters.
        string queryString =
            @"SELECT VALUE Contact FROM AdventureWorksEntities.Contact 
                    AS Contact WHERE Contact.LastName = @ln AND
                    Contact.FirstName = @fn";

        ObjectQuery<Contact> contactQuery =
            new ObjectQuery<Contact>(queryString, advWorksContext);

        // Add parameters to the collection.
        contactQuery.Parameters.Add(new ObjectParameter("ln", "Adams"));
        contactQuery.Parameters.Add(new ObjectParameter("fn", "Frances"));

        // Iterate through the collection of Contact items.
        foreach (Contact result in contactQuery)
            Console.WriteLine("Last Name: {0}; First Name: {1}",
            result.LastName, result.FirstName);
    }
    catch (EntityException ex)
    {
        Console.WriteLine(ex.ToString());
    }
    catch (InvalidOperationException ex)
    {
        Console.WriteLine(ex.ToString());
    }
}

这是查询生成器方法示例。

Dim firstName As String = "Frances"
Dim lastName As String = "Adams"

Using context As New AdventureWorksEntities
    Try
        ' Get the contacts with the specified name.
        Dim contactQuery As ObjectQuery(Of Contact) = _
            context.Contact _
            .Where("it.LastName = @ln AND it.FirstName = @fn", _
            New ObjectParameter("ln", lastName), _
            New ObjectParameter("fn", firstName))

        ' Iterate through the collection of Contact items.
        For Each result As Contact In contactQuery
            Console.WriteLine("Last Name:{0}First Name: {1}", _
            result.LastName, result.FirstName)
        Next

    Catch ex As EntitySqlException
        Console.WriteLine(ex.ToString())
    End Try
End Using

string firstName = @"Frances";
string lastName = @"Adams";

using (AdventureWorksEntities context =
    new AdventureWorksEntities())
{
    try
    {
        // Get the contacts with the specified name.
        ObjectQuery<Contact> contactQuery = context.Contact
            .Where("it.LastName = @ln AND it.FirstName = @fn",
            new ObjectParameter("ln", lastName), 
            new ObjectParameter("fn", firstName));

        // Iterate through the collection of Contact items.
        foreach (Contact result in contactQuery)
            Console.WriteLine("Last Name: {0}; First Name: {1}",
            result.LastName, result.FirstName);
    }
    catch (EntitySqlException ex)
    {
        Console.WriteLine(ex.ToString());
    }
}

另请参见

通过

如何：执行参数化查询（实体框架）

示例

另请参见

任务

概念

其他资源

其他资源