实体框架，跨多个上下文的代码优先和一对多关系 [英] Entity Framework, Code First and One-to-Many relationship across multiple contexts

问题描述

我首先使用VS 2010和Entity Framework代码（版本6）。我在各自的上下文中有两个实体，我想在它们之间创建一对多关系。

I am using VS 2010 and Entity Framework code first (version 6). I have two entities each in its own context and I want to create a one-to-many relationship between them.

上下文1具有以下实体：

Context 1 has the following entity:

public class MyTrust
{
    public int MyTrustID { get; set; }
    public string MyTrustName { get; set; }
}

并且上下文2具有以下实体：

and Context 2 has the following entity:

public class MyLocation
{
    public int MyLocationID { get; set; }
    public int MyTrustID { get; set; }
    public virtual MyTrust MyTrust { get; set; }
}

具有以下Fluent API

with the following Fluent API

modelBuilder.Entity<MyLocation>()
    .HasRequired(m => m.MyTrust);

上下文2的迁移文件包含正确的键，但还为<$ c $创建了一个新表c> MyTrust 在其他上下文中已经存在。

The migration file for Context 2 contains the correct keys but also creates a new table for MyTrust which already exists in the other context.

我知道我可以编辑迁移文件，但这不是解决方案。

I know that I can edit the migration file but that is not a solution.

我的问题是，如何停止第二个 MyTrust 表的创建。

My question is, how to I stop the creation of the second MyTrust table.

更新

上面有一个主要缺陷，就是我将错误的代码粘贴到了上下文2中。现在已更正。抱歉。

There was a major flaw above in that I pasted the wrong code into Context 2. Now corrected. Apologies.

推荐答案

您正在使用所谓的绑定上下文。 Julie Lerman在此博客中解释了此类上下文的好处以及如何使用它们。

You are working with so-called bounded contexts. The benefit of such contexts and how to work with them is explained in this blog by Julie Lerman.

本部分将解决您遇到的所有上下文都不能在迁移中使用的问题：

The problem you experience, none of the contexts can be used in migrations, is addressed in this part:

如果您正在进行新开发，并且想让Code First根据您的类创建或迁移数据库，则需要使用以下命令创建超级模型 DbContext，其中包含构建代表数据库的完整模型所需的所有类和关系。

If you’re doing new development and you want to let Code First create or migrate your database based on your classes, you’ll need to create an "uber-model" using a DbContext that includes all of the classes and relationships needed to build a complete model that represents the database.

请注意，您可以共享如果您遵守以下规则（在Lerman& Miller的书 DbContext ，第233页），则在所有上下文之间输入 MyTrust 类型：

Note that you can share the MyTrust type between all contexts, if you observe these rules (from Lerman & Miller's book DbContext, p 233):

• 一次只能将一个实体附加到一个上下文。这种架构最适合
  的短期生存环境，在这种情况下，要共享的实例在连接到另一个环境之前将完全从一个环境中分离出
  。

更新 >

在EF6中，您可以将多个上下文用于一个迁移路径。参见本演练。

In EF6 you can use multiple contexts for one migration path. See this walkthrough.

这篇关于实体框架，跨多个上下文的代码优先和一对多关系的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！