将属性移动到实体框架代码中的新实体首次迁移 [英] Move property to new Entity in Entity Framework Code First Migration

问题描述

我在项目中使用Entity Framework Code First方法。我有一个数据库迁移的问题。

现在我有实体

  public class Event 
 {
 public int Id {get;组; } 
 public string标题{get;组; } 
 public string City {get;组; 
} 
  

我现有的数据库中已经有数据。现在我想扩展City属性，像这样

  public class Event 
 {
 public int Id {得到;组; } 
 public string标题{get;组; } 
 public virtual Location Location {get;组; 
} 
  

所以，City成为具有许多属性的位置。

  public partial class位置
 {
 public int Id {get;组; } 
 public string国家{get;组; } 
 public string City {get;组; } 
 public string Address {get;组; } 
 public string Place {get;组; } 
} 
  

所以，我需要在活动表中创建行的位置表并复制城市。并将事件定位的外键设置到位置行。但是我不知道如何使用实体框架迁移来移动现有数据。我已经阅读了许多关于实体框架迁移的文章，但没有发现这种情况。

最好的方法是什么？

解决方案

您可以在3个步骤中执行此操作

• 添加位置
• 
  
• 插入位置


• Drop City

/ p>

  public class Event 
 {
 public int Id {get;组; } 
 public string标题{get;组; } 
 public string City {get;组; 
} 
  

• 添加Location属性和类



• 添加位置迁移并更新数据库

  
  
  

  PM>启用迁移

  
  
  

  PM>添加迁移AddLocationTable

  
  
  

  PM>更新数据库




• 创建用于插入数据的空迁移

  
  
  

  PM>添加迁移InsertLocationData

  
  
  

  该类应该有空的 Up 和 Down 方法。
  在 Up 方法中添加以下代码。

    （var context = new AppContext（））
   {
   var events = context.Set< Event>（）。ToArray（）; 
   foreach（事件中的var ev）
   {
   ev.Location = new Location {City = ev.City}; 
  } 
   context.SaveChanges（）; 
  } 
    




• 再次运行迁移以应用 InsertLocationData 迁移。

  
  
  

  PM>更新数据库




• 删除 City 属性，并运行迁移以应用更改。

  
  
  

  PM>添加迁移DropCityFromEvent

  
  
  

  PM>更新数据库

I'm using Entity Framework Code First approach in my project. I have a problem with database migration.

Now I have the entity

public class Event
{
    public int Id { get; set; }
    public string Title { get; set; }
    public string City { get; set; }
}

I have already have data in my existing DataBase. Now I want to extend City property, like this

public class Event
{
    public int Id { get; set; }
    public string Title { get; set; }
    public virtual Location Location { get; set; }
}

so, City become to Location with many properties.

public partial class Location
{
    public int Id { get; set; }
    public string Country { get; set; }
    public string City{ get; set; }
    public string Address { get; set; }
    public string Place { get; set; }
}

So, I need for each row in Events Table create row in Locations Table and copy city. And set foreign key for event localtion to location row.But I don't know how to move existing data using Entity Framework Migration. I have read many post on Entity Framework Migration, but didn't find this case.

What is the best way to do this?

解决方案

You could do that in 3 steps

• Add Location
• Insert Location
• Drop City

Starting from

public class Event
{
    public int Id { get; set; }
    public string Title { get; set; }
    public string City { get; set; }
}

• Add Location property and class

• Add Location migration and update the database

  PM> Enable-Migrations

  PM> Add-Migration AddLocationTable

  PM> Update-Database

• Create empty migration for inserting the data

  PM> Add-Migration InsertLocationData

  The class should have empty Up and Down method. Add following code in the Up method.

  using (var context = new AppContext())
  {
      var events = context.Set<Event>().ToArray();
      foreach (var ev in events)
      {
          ev.Location = new Location { City = ev.City };
      }
      context.SaveChanges();
  }
  

• Run the migration again to apply InsertLocationData migration.

  PM> Update-Database

• Delete City property and run a migration to apply the changes.

  PM> Add-Migration DropCityFromEvent

  PM> Update-Database

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