我可以从指定的迁移中解码EntityFramework模型吗？ [英] Can I get decode an EntityFramework Model from a specified migration?

问题描述

显然，IMigrationMetadata.Target对EF模型的状态进行编码。
我可以用它来为特定的迁移重建模型吗？

Apparently IMigrationMetadata.Target encodes the state of the EF model. Can I use this to reconstruct the model for a particular migration?

推荐答案

是的，有可能。我自己很好奇那些魔术资源字符串到底存储了什么。通过深入研究实体框架源代码（请参见 DbMigrator.GetLastModel（）方法），我发现 IMigrationMetadata.Target 仅存储包含gzip压缩XML的base-64字符串数据。为了测试这一点，我创建了一个新的控制台应用程序，其中包含一个简单的代码优先模型，定义如下：

Yes, it is possible. I was myself curious what exactly those magic resource strings were storing. By digging into the Entity Framework source (see the DbMigrator.GetLastModel() method), I found out that the IMigrationMetadata.Target just stores a base-64 string containing gzipped XML data. To test this, I created a new console application containing a simple code-first model defined as follows:

public class ContactContext : DbContext
{
    public virtual IDbSet<Contact> Contacts { get; set; }
}

public class Contact 
{
    public int Id {get; set;}
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

然后，我使用NuGet软件包管理器控制台创建了迁移：

Then I created a migration using the NuGet Package Manager Console:

PM> Enable-Migrations
PM> Add-Migration MyMigration

接下来，我将以下代码添加到应用程序的 Main（ ）方法来解码该字符串中的值并将其转储到控制台：

Next I added the following code to my application's Main() method to decode the value in that string and dump it to the console:

var migration = new MyMigration();
var metadata = (IMigrationMetadata)migration;
var compressedBytes = Convert.FromBase64String(metadata.Target);
var memoryStream = new MemoryStream(compressedBytes);
var gzip = new GZipStream(memoryStream, CompressionMode.Decompress);
var reader = new StreamReader(gzip);
Console.WriteLine(reader.ReadToEnd());

此输出一个EDMX文件，该文件表示与创建迁移的我 DbContext 关联的实体数据模型。如果我将此输出写入扩展名为 .edmx 的文件中，则可以使用Visual Studio将其打开并在实体设计器中查看。

This outputs an EDMX file representing the Entity Data Model associated with my DbContext that created the migration. If I write this output to a file with the .edmx extension, I'm able to open it with Visual Studio and view it in the Entity Designer.

然后，如果由于某种原因我想重新生成 DbContext 和生成模型的实体类，则需要仅执行以下操作：

Then if for some reason I wanted to regenerate the DbContext and entity classes that produced the model, I would need only do the following:

1. 将 .edmx 文件添加到Visual Studio项目中。


2. 安装用于C＃的EF 5.x DbContext Generator （如果我还没有的话）。


3. 通过选择添加->添加相关的T4模板。


4. 修改新添加的 .tt 文件，替换 $ edmxInputFile $ ，其文件名为我的 .edmx 文件。


5. 观看两个模板神奇地将我的代码优先类型重新生成为各自的 .cs 文件。

1. Add the .edmx file to a Visual Studio project.
2. Install the EF 5.x DbContext Generator for C# if I don't already have it.
3. Add the related T4 templates by selecting Add -> New Item from project node context menu.
4. Modify the newly added .tt files, replacing $edmxInputFile$ with the name of my .edmx file.
5. Watch as the two templates magically regenerate my code-first types to their respective .cs files.

<希望能回答您的问题！ :-D

Hope that answers your question! :-D

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