如何：查看存储命令（实体框架）

本主题演示如何使用 ToTraceString 方法来查看实体框架中 ObjectQuery 的存储命令。本主题中的示例演示如何查看一个查询的存储命令，该查询从 Production.Product 表返回 Product 对象。将使用以下每种 实体框架 查询技术演示同一示例：

• LINQ to Entities

• Entity SQL with ObjectQuery<T>

• ObjectQuery <T> 的查询生成器方法

本主题中的示例基于 Adventure Works 销售模型。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

这是 LINQ to Entities 示例。

Using advWorksContext As New AdventureWorksEntities()
    Try
        ' Define an ObjectQuery to use with the LINQ query.
        Dim products As ObjectQuery(Of Product) = advWorksContext.Product

        ' Define a LINQ query that returns a selected product.
        Dim result = From product In products _
                     Where product.ProductID = 900 _
                     Select product

        ' Cast the inferred type to a ObjectQuery
        ' and then write the store commands for the query.
        Console.WriteLine(CType(result, ObjectQuery(Of Product)).ToTraceString())
    Catch ex As EntitySqlException
        Console.WriteLine(ex.ToString())
    End Try
End Using

using (AdventureWorksEntities advWorksContext =
    new AdventureWorksEntities())
{
    try
    {
        // Define an ObjectQuery to use with the LINQ query.
        ObjectQuery<Product> products = advWorksContext.Product;

        // Define a LINQ query that returns a selected product.
        var result = from product in products 
                     where product.ProductID == 900
                     select product;

        // Cast the inferred type var to an ObjectQuery
        // and then write the store commands for the query.
        Console.WriteLine(((ObjectQuery<Product>)result).ToTraceString());
    }
    catch (EntitySqlException ex)
    {
        Console.WriteLine(ex.ToString());
    }
}

这是 Entity SQL 示例。

Using advWorksContext As New AdventureWorksEntities
    Try
        ' Define the Entity SQL query string.
        Dim queryString As String = _
            "SELECT VALUE Product FROM AdventureWorksEntities.Product AS Product " & _
            "WHERE Product.ProductID = 900"

        ' Define the object query with the query string.
        Dim productQuery As New ObjectQuery(Of Product) _
            (queryString, advWorksContext, MergeOption.AppendOnly)

        ' Write the store commands for the query.
        Console.WriteLine(productQuery.ToTraceString())
    Catch ex As EntitySqlException
        Console.WriteLine(ex.ToString)
    End Try
End Using

using (AdventureWorksEntities advWorksContext =
    new AdventureWorksEntities())
{
    try
    {
        // Define the Entity SQL query string.
        string queryString =
            @"SELECT VALUE Product FROM AdventureWorksEntities.Product AS Product 
          WHERE Product.ProductID = 900";

        // Define the object query with the query string.
        ObjectQuery<Product> productQuery =
            new ObjectQuery<Product>(queryString, advWorksContext, MergeOption.AppendOnly);

        // Write the store commands for the query.
        Console.WriteLine(productQuery.ToTraceString());
    }
    catch (EntitySqlException ex)
    {
        Console.WriteLine(ex.ToString());
    }
}

这是查询生成器方法示例。

Using advWorksContext As New AdventureWorksEntities()
    Try
        ' Define the object query for the specific product.
        Dim productQuery As ObjectQuery(Of Product) = _
            advWorksContext.Product.Where("it.ProductID = 900")

        ' Write the store commands for the query.
        Console.WriteLine(productQuery.ToTraceString())
    Catch ex As EntitySqlException
        Console.WriteLine(ex.ToString())
    End Try
End Using

using (AdventureWorksEntities advWorksContext =
    new AdventureWorksEntities())
{
    try
    {
        // Define the object query for the specific product.
        ObjectQuery<Product> productQuery =
            advWorksContext.Product.Where("it.ProductID = 900");

        // Write the store commands for the query.
        Console.WriteLine(productQuery.ToTraceString());
    }
    catch (EntitySqlException ex)
    {
        Console.WriteLine(ex.ToString());
    }
}

另请参见

概念

对象查询（实体框架）
查询生成器方法（实体框架）
Entity SQL 概述

其他资源

LINQ to Entities
查询实体数据模型（实体框架任务）