如何在EF4中查询多对多映射？ [英] How do I query many-to-many mapping in EF4?

问题描述

我有一个非常简单的问题，一个不太明显的解决方案。我在我的数据库中有一个关系映射在用户和角色之间，每个用户可以映射到一个或多个角色。所以映射如下：

用户< 1：n> UserRole< n：1>角色

在我生成的EF4 POCO中，用户和角色各有一个ICollection：

  public class User 
 {
 //束其他属性/方法
 
 public virtual ICollection< ;作用>角色
} 
 
 public class Role 
 {
 //束其他属性/方法
 
 public virtual ICollection< User>用户
} 
  

现在，我已经实现了IoC，UoW和存储库模式在这篇文章，它使用ObjectSet通过存储库获取/保存数据。

我的问题是，如何实现：

  public bool UserIsInRole（int userId，int roleId）
  

我尝试了以下内容：

  public bool UserIsInRole（int userId，int roleId）
 {
角色角色= _roleRepository.Single（r => r.Id == roleId）; 
 return _userRepository.SingleOrDefault（u => u.Roles.Contains（role））！= null; 
} 
  

但是失败：

无法创建Data.Models.Role类型的常量值。在这种情况下，只支持原始类型（如Int32，String和Guid）。

另外，它不是一个

我正在寻找这样的东西：

  return _userRepository.SingleOrDefault（u => u.Roles.Where（r => r.Id = roleId））; 
  

但ICollection不支持LINQ。

如何做到这一点，理想情况下，如何使用一个LINQ表达式和一次访问数据库？

或者，我是否完全出错？

提前感谢

已解决：
感谢所有发贴的人。都给了可以接受的答案。我接受了最优雅的一个。

解决方案

有一个更简洁的方法：

  public bool UserIsInRole（int userId，int roleId）
 {
 return _userRepository。 
 Any（u => u.Id == userId&& 
 u.Roles.Any（r => r.Id == roleId））; 
} 
  

I have a pretty simple problem with a not-so-obvious solution. I have a relational mapping in my database between Users and Roles, and each user can be mapped to one or more roles. So the mapping is like so:

User < 1:n > UserRole < n:1 > Role

In my generated EF4 POCOs, User and Role each have an ICollection of the other:

public class User 
{
    //Bunch of other properties/methods

    public virtual ICollection<Role> Roles
}

public class Role
{
    //Bunch of other properties/methods

    public virtual ICollection<User> Users
}

Now, I've implemented the IoC, UoW, and repository patterns illustrated in this article, which uses an ObjectSet to fetch/persist the data via repositories.

My question is, how do I implement this:

public bool UserIsInRole(int userId, int roleId)

I have tried the following:

public bool UserIsInRole(int userId, int roleId)
{
    Role role = _roleRepository.Single(r => r.Id == roleId);
    return _userRepository.SingleOrDefault(u => u.Roles.Contains(role)) != null;
}

But it fails with:

Unable to create a constant value of type 'Data.Models.Role'. Only primitive types ('such as Int32, String, and Guid') are supported in this context.

Plus, it's not a very elegant implementation as it's having to hit the database twice.

I was looking for something like this:

return _userRepository.SingleOrDefault(u => u.Roles.Where(r => r.Id = roleId));

But ICollection doesn't support LINQ.

How can I do this, and ideally, how can I do it with one LINQ expression and one trip to the database?

Or, am I going about this completely wrong?

Thanks in advance.

Solved: Thanks to all who posted. All gave an acceptable answer. I accepted the one that was the most elegant.

解决方案

There is a more concise way to do it:

public bool UserIsInRole(int userId, int roleId)
{
    return _userRepository.
            Any(u => u.Id == userId && 
                     u.Roles.Any(r => r.Id == roleId));
}

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