包含多个结果集的存储过程Stored Procedures with Multiple Result Sets

10/23/2016

本文内容

有时，在使用存储过程时，您需要返回多个结果集。Sometimes when using stored procedures you will need to return more than one result set. 此方案通常用于减少构成单个屏幕所需的数据库往返次数。This scenario is commonly used to reduce the number of database round trips required to compose a single screen.在 EF5 之前，实体框架允许调用存储过程，但只将第一个结果集返回给调用代码。Prior to EF5, Entity Framework would allow the stored procedure to be called but would only return the first result set to the calling code.

本文将介绍两种方法，可用于从实体框架中的存储过程访问多个结果集。This article will show you two ways that you can use to access more than one result set from a stored procedure in Entity Framework. 一个只使用代码，并处理代码 first 和 EF 设计器，另一个仅适用于 EF 设计器的。One that uses just code and works with both Code first and the EF Designer and one that only works with the EF Designer. 此方面的工具和 API 支持应在实体框架的未来版本中得以改善。The tooling and API support for this should improve in future versions of Entity Framework.

“模型”Model

本文中的示例使用的是基本的博客和文章模型，其中的博客包含多篇文章，张贴内容属于单个博客。The examples in this article use a basic Blog and Posts model where a blog has many posts and a post belongs to a single blog. 我们将使用数据库中的存储过程，该存储过程返回所有博客和帖子，如下所示：We will use a stored procedure in the database that returns all blogs and posts, something like this:

CREATE PROCEDURE [dbo].[GetAllBlogsAndPosts]

AS

SELECT * FROM dbo.Blogs

SELECT * FROM dbo.Posts

用代码访问多个结果集Accessing Multiple Result Sets with Code

我们可以执行使用代码发出原始 SQL 命令，以执行存储过程。We can execute use code to issue a raw SQL command to execute our stored procedure. 此方法的优点是它适用于代码 first 和 EF 设计器。The advantage of this approach is that it works with both Code first and the EF Designer.

为了获得多个结果集，我们需要使用 IObjectContextAdapter 接口删除 ObjectContext API。In order to get multiple result sets working we need to drop to the ObjectContext API by using the IObjectContextAdapter interface.

获得 ObjectContext 后，我们可以使用转换方法将存储过程的结果转换为可在 EF 中跟踪和使用的实体。Once we have an ObjectContext then we can use the Translate method to translate the results of our stored procedure into entities that can be tracked and used in EF as normal. 下面的代码示例演示如何执行此操作。The following code sample demonstrates this in action.

using (var db = new BloggingContext())

{

// If using Code First we need to make sure the model is built before we open the connection

// This isn't required for models created with the EF Designer

db.Database.Initialize(force: false);

// Create a SQL command to execute the sproc

var cmd = db.Database.Connection.CreateCommand();

cmd.CommandText = "[dbo].[GetAllBlogsAndPosts]";

try

{

db.Database.Connection.Open();

// Run the sproc

var reader = cmd.ExecuteReader();

// Read Blogs from the first result set

var blogs = ((IObjectContextAdapter)db)

.ObjectContext

.Translate(reader, "Blogs", MergeOption.AppendOnly);

foreach (var item in blogs)

{

Console.WriteLine(item.Name);

}

// Move to second result set and read Posts

reader.NextResult();

var posts = ((IObjectContextAdapter)db)

.ObjectContext

.Translate(reader, "Posts", MergeOption.AppendOnly);

foreach (var item in posts)

{

Console.WriteLine(item.Title);

}

}

finally

{

db.Database.Connection.Close();

}

}

转换方法接受我们在执行过程、EntitySet 名称和 MergeOption 时收到的读取器。The Translate method accepts the reader that we received when we executed the procedure, an EntitySet name, and a MergeOption. EntitySet 名称将与派生上下文上的 DbSet 属性相同。The EntitySet name will be the same as the DbSet property on your derived context. MergeOption 枚举控制在内存中已存在相同的实体时如何处理结果。The MergeOption enum controls how results are handled if the same entity already exists in memory.

在这里，我们将循环访问博客的集合，然后调用 NextResult，这对于上述代码非常重要，因为在移动到下一个结果集之前必须使用第一个结果集。Here we iterate through the collection of blogs before we call NextResult, this is important given the above code because the first result set must be consumed before moving to the next result set.

一旦调用这两个转换方法，EF 就会以与任何其他实体相同的方式跟踪博客和公告实体，因此可以修改或删除它们并将其保存为正常。Once the two translate methods are called then the Blog and Post entities are tracked by EF the same way as any other entity and so can be modified or deleted and saved as normal.

备注

当使用转换方法创建实体时，EF 不会考虑任何映射。EF does not take any mapping into account when it creates entities using the Translate method. 它只是将结果集中的列名称与类的属性名进行匹配。It will simply match column names in the result set with property names on your classes.

备注

这种情况下，如果启用了延迟加载，则访问其中一个博客实体上的 "发布" 属性后，EF 将连接到数据库以延迟加载所有发布，即使我们已经加载了所有发布。That if you have lazy loading enabled, accessing the posts property on one of the blog entities then EF will connect to the database to lazily load all posts, even though we have already loaded them all. 这是因为 EF 无法知道是否已加载所有发布或数据库中是否存在其他内容。This is because EF cannot know whether or not you have loaded all posts or if there are more in the database. 如果要避免这种情况，则需要禁用延迟加载。If you want to avoid this then you will need to disable lazy loading.

在 EDMX 中配置的多个结果集Multiple Result Sets with Configured in EDMX

备注

必须针对 .NET Framework 4.5，才能在 EDMX 中配置多个结果集。You must target .NET Framework 4.5 to be able to configure multiple result sets in EDMX. 如果面向的是 .NET 4.0，则可以使用上一节中所示的基于代码的方法。If you are targeting .NET 4.0 you can use the code-based method shown in the previous section.

如果使用的是 EF 设计器，则还可以修改模型，使其了解将返回的不同结果集。If you are using the EF Designer, you can also modify your model so that it knows about the different result sets that will be returned. 在手头之前需要了解的一点是，该工具不是多个结果集感知，因此您需要手动编辑该 edmx 文件。One thing to know before hand is that the tooling is not multiple result set aware, so you will need to manually edit the edmx file. 编辑此类 edmx 文件的操作将起作用，但它也会破坏 VS 中模型的验证。Editing the edmx file like this will work but it will also break the validation of the model in VS. 如果验证模型，将始终会出现错误。So if you validate your model you will always get errors.

要执行此操作，您需要将该存储过程添加到您的模型中，就像对单个结果集查询执行此操作一样。In order to do this you need to add the stored procedure to your model as you would for a single result set query.

完成后，需要右键单击模型，然后选择 "打开方式"。Once you have this then you need to right click on your model and select Open With.. then Xmlthen Xml

将模型作为 XML 打开后，需要执行以下步骤：Once you have the model opened as XML then you need to do the following steps:

在模型中查找复杂类型和函数导入：Find the complex type and function import in your model:

...

...

...

删除复杂类型Remove the complex type

更新函数 import，使其映射到你的实体，在本例中，它将如下所示：Update the function import so that it maps to your entities, in our case it will look like the following:

这会告知模型，存储过程将返回两个集合：一个博客项和一个发布项。This tells the model that the stored procedure will return two collections, one of blog entries and one of post entries.

查找函数映射元素：Find the function mapping element:

...

...

将结果映射替换为每个要返回的实体，如下所示：Replace the result mapping with one for each entity being returned, such as the following:

还可以将结果集映射到复杂类型，如默认创建的类型。It is also possible to map the result sets to complex types, such as the one created by default. 为此，您创建了一个新的复杂类型，而不是删除它们，并使用在上述示例中使用了实体名称的任何位置的复杂类型。To do this you create a new complex type, instead of removing them, and use the complex types everywhere that you had used the entity names in the examples above.

更改这些映射后，你可以保存模型并执行以下代码以使用该存储过程：Once these mappings have been changed then you can save the model and execute the following code to use the stored procedure:

using (var db = new BlogEntities())

{

var results = db.GetAllBlogsAndPosts();

foreach (var result in results)

{

Console.WriteLine("Blog: " + result.Name);

}

var posts = results.GetNextResult();

foreach (var result in posts)

{

Console.WriteLine("Post: " + result.Title);

}

Console.ReadLine();

}

备注

如果手动编辑模型的 edmx 文件，则从数据库重新生成模型时，它将被覆盖。If you manually edit the edmx file for your model it will be overwritten if you ever regenerate the model from the database.

摘要Summary

这里，我们介绍了两种不同的方法来使用实体框架访问多个结果集。Here we have shown two different methods of accessing multiple result sets using Entity Framework. 这两种方法都是相同的，具体取决于你的情况和首选项，你应选择最适合你的环境的方法。Both of them are equally valid depending on your situation and preferences and you should choose the one that seems best for your circumstances. 它计划在未来版本的实体框架中对多个结果集的支持进行改进，并且不再需要执行本文档中的步骤。It is planned that the support for multiple result sets will be improved in future versions of Entity Framework and that performing the steps in this document will no longer be necessary.