实体框架 - 实体只读属性映射到相关列的列 [英] Entity Framework - Entity read-only property mapped to a column of related table

问题描述

我有一个有趣的问题需要解决，但是虽然很常见，但实际框架看起来并不容易实现。有两个表：

I have interesting problem to solve but, although common, it looks like it's not easily achievable with Entity Framework. There are two tables:

Player(Id,TeamId,FirstName,LastName)
Team(Id, Name, IsProfessional)

玩家只能属于一个团队。使用TPT（DB首先），我们有两个类映射到这些表：

Player can belong only to one team. Using TPT (DB first), we have two classes mapped to those tables:

public class Player
{
   public int Id{get;set;}
   public int TeamId{get;set;}
   public string FirstName{get; set;}
   public string LastName{get; set;}
   public Team Team{get;set;}
}

public class Team
{ 
   public int Id{get; set;}
   public string Name{get;set;}
   public bool IsProfessional{get;set;}
   public IEnumerable<Player> Players{get;}
}

我想要实现的是属性IsProfessional on Player实体：

What I would like to achieve is property IsProfessional on Player entity:

public class Player
    {
       public int Id{get;set;}
       public int TeamId{get;set;}
       public string FirstName{get; set;}
       public string LastName{get; set;}
       public Team Team{get;set;}
       **public bool IsProfessional{get;}** should be read-only
    }

是否可以配置映射方式IsProfessional属性可以在linq查询中使用？

Is it possible to configure mapping that way IsProfessional property can be used in linq queries?

var result= db.Players.Where(p=>p.IsProfessional==true);

并且每当玩家实体实现时填充该字段？

and to have that field populated every time Player entity is materialized?

Player pl = db.Players.Where(p=>p.FirstName="Lionel").FirstOrDefault();
if(pl.IsProfessional)
{
//do something...
}

已尝试使用：

• 实体拆分。不可能，因为我想保持团队映射，因为关系不是1：1）


• 将Player实体映射到数据库视图。不喜欢它，因为还有其他关系我需要的玩家实体。我知道可以手动创建它们，但从数据库更新edmx将重置ssdl。

• Entity Splitting. Not possible because I want to keep Team mapping and because relationship is not 1:1)
• Mapping Player entity to a db view. Didn't like it because there are other relationships Player entity has that I need. I know it is possible to create them manually, but updating edmx from database will reset ssdl.

谢谢

解决方案

根据Gert Arnold答案中的第二个选项，适合我需求的解决方案如下： / p>

Based on second option in Gert Arnold answer, solution that fits my needs is as follows:

1. 我创建函数 GetIsProfessional （必须这样做，因为计算字段通常只能从自己的表格中进行）

1. I create function GetIsProfessional (had to do it because computed fields normally can be made only from own table fields)

CREATE FUNCTION [dbo].[GetIsProfessional](@teamId as INT)
RETURNS bit

BEGIN

DECLARE @isProfi AS bit

SELECT @isProfi = IsProfessional
FROM Teams
WHERE Id = @teamId

RETURN @isProfi

END

我创建了 Player 表

ALTER TABLE Players ADD [IsProfessional] AS dbo.GetIsProfessional(TeamId)

使用db第一个方法，我jus从数据库更新模型就是这样，我可以查询该字段，并且在Player对象实现时预先填充。

As I'm using db first approach, I just update model from database and that's it, I can query on that field and it's pre populated when Player object is materialized.

推荐答案

这不能用EF完成。有些选项并不完全符合您的要求，但是几乎或多或少地接近：

This can't be done with EF. There are some options that don't do exactly what you want, but get close more or less:

1. 创建属性 TeamPlayers 在您的上下文中返回包含该团队的玩家，以便您始终可以执行 player.Team.IsProfessional 甚至当上下文已经被放弃时。

1. Create a property TeamPlayers in your context that returns the players with the team included, so that you can always do player.Team.IsProfessional even when the context has already been diposed.

public IQueryable<PLayer> TeamPlayers
{
    get { return this.Players.Include("Team"); }
}

在数据库表中创建一个计算字段并映射到它与 DatabaseGeneratedOption.Computed 。

在中创建一个静态属性Player 返回访问 Team.IsProfessional 的表达式（需要包含生活环境或团队）：

Create a static property in Player that returns the expression that accesses Team.IsProfessional (requires a living context or team included):

public static Expression<Func<PLayer, bool>> IsProfessional
{
    get { return p => p.Team.IsProfessional; }
}
...
db.Players.Where( p=> p.FirstName="Lionel").Where(Player.IsProfessional)....

我宁愿计算字段，因为它总是填充，所以你可以在内部和外部的范围内使用它。

I would prefer the calculated field, because it is always populated, so you can use it inside and outside the scope of a context.

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