以编程方式检索流利的配置，而无需实例化DbContext [英] Retrieving fluent configuration programmatically without instantiating DbContext

问题描述

我有一个DbContext派生类，其成员实体类是使用Fluent API配置的。我想以编程方式检索这些配置和关系。

I have a DbContext derived class whose member entity classes are configured using Fluent API. I want to retrieve these configurations and relationships programmatically. the code to do this is already in place and I am porting it to a T4 template for code generation.

虽然大多数代码生成使用反射，但流畅的配置需要使用以下代码：要实例化的上下文类，以便获得：

While most of the code generation uses reflection, fluent configuration requires the context class to be instantiated in order to get:

• ObjectContext


• EntityObjects


• EntityContainer


• EntitySets


• Etcetera

• ObjectContext
• EntityObjects
• EntityContainer
• EntitySets
• Etcetera

因为我们没有使用属性属性，所以反射没有帮助。

Since we are not using property attributes, reflection is of no help.

这在运行时效果很好，但是在T4模板中实例化DbContext会导致所有错误。各种各样的问题。有时它会导致VS崩溃，产生奇怪的错误，创建周期性依赖关系等。

This works fine during runtime, but instantiating the DbContext within a T4 template is causing all sorts of problems. It sometimes crashes VS, gives weird errors, creates a cyclic dependency, etc.

如果我调试T4模板，它的确运行没有错误，但是后台进程锁定了项目包含DbContext类和实体。因此，每次对实体进行更改时，我必须重新启动VS三次，执行不同的步骤。

If I debug the T4 template, it does run without errors but the background process locks the project containing the DbContext class and entities. So every time there is a change to the entities, I have to restart VS three times performing different steps. Yuck!

我想知道是否存在一种无需实例化上下文类即可检索实体元数据/配置的方法。

I was wondering if there is a way to retrieve entity metadata/configuration without instantiating the context class. Any guidance would be appreciated.

推荐答案

好，您需要加载上下文，因为它需要调用 OnModelBuilding（DbModelBuilder）至少要做一次生意；

Well, you need to load the context because it needs to call OnModelBuilding(DbModelBuilder) at least once to do it's business; otherwise there is no model to interrogate.

如果需要，可以使用 EdmxWriter ;

If you want, you can store off the information as XML using EdmxWriter;

    public static string ToEdmx(this System.Data.Entity.DbContext context)
    {
        var sb = new StringBuilder();

        using (var textWriter = new StringWriter(sb))
        using (var xmlWriter = System.Xml.XmlWriter.Create(textWriter, new System.Xml.XmlWriterSettings { Indent = true, IndentChars = "    " }))
        {
            System.Data.Entity.Infrastructure.EdmxWriter.WriteEdmx(context, xmlWriter);
            textWriter.Flush();
        }

        return sb.ToString();
    }

这将为您提供带有数据模型的XML文档。您可能可以通过一个进程将其保存到磁盘，然后在TT文件中查询该文件。

This will give you an XML document with the data model. You can probably save that to disk in one process, and interrogate that file in your TT file.

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