多个DbContexts在一个数据库与代码优先迁移 [英] Multiple DbContexts on one DB with Code First Migrations

问题描述

我偶然发现了与这个问题。此外，我不想从数据库中删除__migrationHistory表。

I stumbled uppon the same problem as described in this question. In addition, i didn't want to loose the __migrationHistory table from the database.

我尝试使用一个使用一个超级上下文的解决方案，其中包含所有DbSet< ;> s并使用正常的Contexts，但我有一个错误。 （模型支持DbContext已被更改）
如果您只是从SQL服务器中删除__migrationHistory表，但是正如我所说，我想保留历史记录，这很容易避免。

I tried it with the suggested Solution of using one "super" context which contains all DbSet<>s and using the normal Contexts, but i got a error. ("Model backing DbContext has been changed") This is easily avoidable if you just kill the __migrationHistory table from the SQL server, but as i said, i want to keep the history.

我发现一个简单而简单的解决方案，请看下面我的答案。

I found a simple and easy solution, see my answer below.

推荐答案

首先，你必须为迁移配置创建一个超级上下文。

First, you have to create a "Super" Context for the Migrations Configuration.

MySuperContext : DbContext
{
    // All DbSet<> s from your different contexts have to be referenced here once, you will only use this class for the migrations.

    public MySuperContext() : base("YourConnectionString")
    {
        System.Data.Entity.Database.SetInitializer(new MigrateDatabaseToLatestVersion<MySuperContext, MyMigrationsConfiguration>());
    }
}

然后只需创建以下类：

public class NoDatabaseInitializer<T> : IDatabaseInitializer<T> where T: DbContext
{
    public void InitializeDatabase(T context)
    {
        // Do nothing, thats the sense of it!
    }
}

现在，在每个小型上下文中，添加对于构造函数：

now, in every small Context you have, add this to the constructor:

class MyUserContext : DbContext
{
    public MyUserContext : base("MyConnectionString") // Can be a user context, etc
    {
        System.Data.Entity.Database.SetInitializer(new NoDatabaseInitializer<MyContext>());
    }
}

现在你不会再收到这个错误，

plus，您将拥有您的迁移历史记录，

，您将在一个数据库中使用多个上下文。

now you won't get this error any more,
plus, you will have your migration-History,
and you will use multiple Contexts on one Database.

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