多对多与相关 ViewModel DTO C#

Question

我在 NetCore C# 项目中有 3 个表，我无法对数据库进行查询以形成附加角色的用户的完整列表

用户表

var user = await _context.Users
    .Select(x => new
    {
        x.Id,
        x.UserName           
    }).ToListAsync();

角色表

var role = await _context.Roles
    .Select(x => new
    {
        RoleId = x.Id,
        RoleName = x.Name
    }).ToListAsync();

和UserRole表（关系）

var userRole = await _context.UserRoles
    .Select(x => new
    {
        x.RoleId,
        x.UserId
    }).ToListAsync();

您需要如何构建查询以生成此 DTO？

public class UserRoleDto
{
    public int UserId { get; set; }
    public string UserName { get; set; }

    public IEnumerable<RolesDto> Roles { get; set; }

}

public class RolesDto
{
    public int RoleId { get; set; }

    public string RoleName { get; set; }
}

并显示了这个结果？

[
    {
        "userId": "1",
        "userName": "User1",
        "roles": [
            {
                "roleId": "1",
                "roleName": "admin"
            },
            {
                "roleId": "2",
                "roleName": "operator"
            },
            {
                "roleId": "3",
                "roleName": "support"
            }
        ]
    },
    {
        "userId": "2",
        "userName": "User2",
        "roles": [
            {
                "roleId": "2",
                "roleName": "operator"
            }
        ]
    }
]

Answer 1

我对此的第一印象是您的联接表 UserRole 可能如下所示：

public class UserRole
{
    public int UserId {get; set;}
    public int RoleId {get; set;}
}

这很好，但它缺少满足 DTO 要求的导航属性。 您的目标应该是将连接表作为

public class UserRole
{
    public int UserId {get; set;}
    public int RoleId {get; set;}
    public Role Role {get; set;}
    public User User {get; set;}
}

你几乎得到了正确的查询，它没有经过测试，但试试这样的：

var userRole = await _context.UserRoles
    .Select(x => new UserRoleDto()  
    {
       UserId = x.User.Id,
       UserName = x.User.Name,
       Roles = new List<RolesDto>()
       {
           new RolesDto()
           {
              RoleId = x.Role.Id,
              RoleName = x.Role.Name
           }
       }
    }).ToListAsync();

Answer 2

改变

public class UserRoleDto
{
    public int UserId { get; set; }
    public string UserName { get; set; }

    public IEnumerable<RolesDto> Roles { get; set; }

}

到

public class UserRoleDto
{
    public int UserId { get; set; }
   
 public int RoleId{ get; set; }
}

并进行查询以加入用户和角色。在此之后使用此帖子Build JSON Hierarchy from Structured Data 转换为 json。

Answer 3

可以在 OnModelCreating 中配置多对多

modelBuilder.Entity<User>()
   .HasMany(b => b.Roles)
   .WithMany(c => c.Users)
   .Map(cs =>
   {
       cs.MapLeftKey("UserId");
       cs.MapRightKey("RoleId");
       cs.ToTable("UserToRole");
   });

Answer 4

考虑不包括 -

public DbSet<UserRole> UserRoles { get; set; }

在您的DbContext 班级中。这是因为UserRole 是一个连接实体，而连接实体不是以模型为中心的概念。它们的存在纯粹是一个以关系数据库为中心的想法。所以，尽量不要直接查询加入实体。

将模型定义为 -

public class User
{
    public int Id { get; set; }
    public string Name { get; set; }

    public IList<UserRole> UserRoles { get; set; }
}

public class Role
{
    public int Id { get; set; }
    public string Name { get; set; }

    public IList<UserRole> UserRoles { get; set; }
}

public class UserRole
{
    public int UserId { get; set; }
    public int RoleId { get; set; }

    public User User { get; set; }
    public Role Role { get; set; }  
}

你的查询可以像 -

var result = await _context.Users.Select(
    u => new UserRoleDto
    {
        UserId = u.Id,
        UserName = u.Name,
        Roles = u.UserRoles.Select(x => new RolesDto { RoleId = x.RoleId, RoleName = x.Role.Name }).ToList()
    }).ToListAsync();

Answer 5

我用给定的解决方案实现了它

var users = await _context.Users.Select(x => new { x.Id, x.UserName }).ToListAsync();
var userRoles = await _context.UserRoles.ToListAsync();
var roles = await _context.Roles.ToListAsync();

var result = users.Select(x => new
{
    UserId = x.Id,
    x.UserName,
    Roles = userRoles
        .Where(y => y.UserId == x.Id)
        .Join(roles, r => r.RoleId, r => r.Id, (u, r) => new
        {
            RoleId = r.Id,
            RoleName = r.Name
        }).ToList()
    }); 
return Ok(result);