Entity Framework Core 5.0 如何将 LINQ 转换为多对多连接以使用交集 table 作为 ASP.NET 成员资格

Question

问题： 如何转换 LINQ 查询以对子 select 执行 LEFT OUTER JOIN，INNER JOIN 两个 tables 并具有谓词？

上下文： 我正在使用 EFCore Tools 逆向工程 功能从 Entity Framework 6 (EF6) 升级到 Entity Framework Core 5 (EFCore)。我有一个使用 LINQ 查询 ASP.NET Membership 系统上 AspNet_Users 和 AspNet_Roles table 之间的多对多关系的查询。查询通过 AspNet_UsersInRoles 交集 table 抽象出连接。结果，在 EF6 中我有以下 LINQ：

(from r in this.DbContext.aspnet_Users
where r.UserId == dpass.UserId
select r.aspnet_Roles.Select(x => x.RoleName)
).FirstOrDefault();

生成以下 SQL 查询（使用 SQL Server Profiler 检索）：

DECLARE @p__linq__0 uniqueidentifier = '<Runtime_GUID>'

SELECT 
    [Limit1].[UserId] AS [UserId], 
    [Join1].[RoleName] AS [RoleName], 
    CASE WHEN ([Join1].[UserId] IS NULL) THEN CAST(NULL AS int) ELSE 1 END AS [C1]
FROM (SELECT TOP (1) [Extent1].[UserId] AS [UserId]
        FROM [dbo].[aspnet_Users] AS [Extent1]
        WHERE [Extent1].[UserId] = @p__linq__0 
        ) AS [Limit1]
LEFT OUTER JOIN (SELECT [Extent2].[UserId] AS [UserId]
                    , [Extent3].[RoleName] AS [RoleName]
                FROM [dbo].[aspnet_UsersInRoles] AS [Extent2]
                INNER JOIN [dbo].[aspnet_Roles] AS [Extent3] 
                    ON [Extent3].[RoleId] = [Extent2].[RoleId] 
                ) AS [Join1] 
    ON [Limit1].[UserId] = [Join1].[UserId]

我已将 LINQ 转换为以下内容：

(from ur in this.DbContext.aspnet_UsersInRoles
 join r in this.DbContext.aspnet_Roles 
    on ur.RoleId equals r.RoleId
  where ur.UserId == dpass.UserId
  join u in this.DbContext.aspnet_Users
    on ur.UserId equals u.UserId
 into UserRolesJoined from UserRoles in UserRolesJoined.DefaultIfEmpty()                              
  select new { ur.UserId, ur.Role.RoleName }
 )

生成以下 SQL 查询（使用 EFCore 的新 .ToQueryString() 方法检索）：

DECLARE @__dpass_UserId_1 uniqueIdentifier = '<Runtime_GUID>'
SELECT [a].[UserId], [a2].[RoleName]
FROM [aspnet_UsersInRoles] AS [a]
INNER JOIN [aspnet_Roles] AS [a0] ON [a].[RoleId] = [a0].[RoleId]
LEFT JOIN [aspnet_Users] AS [a1] ON [a].[UserId] = [a1].[UserId]
INNER JOIN [aspnet_Roles] AS [a2] ON [a].[RoleId] = [a2].[RoleId]
WHERE [a].[UserId] = @__dpass_UserId_1

来自 EFCore 的 SQL SELECT 语句不同于 SQL SELECT 语句来自 EF6；但是，SQL Select 结果是相同的。这是重写 LINQ 的正确方法，还是我弄错了？非常感谢任何帮助。

更新

一旦我运行逆向工程工具，原来的LINQ命令有以下错误：

CS1061 'aspnet_Users' 不包含 'aspnet_Roles' 的定义，并且找不到接受类型 'aspnet_Users' 的第一个参数的可访问扩展方法 'aspnet_Roles' （您是否缺少 using 指令或程序集引用？）

当我将 public IEnumerable<object> aspnet_Roles; 添加到 aspnet_users 时，出现以下错误。

CS1061 'object' 不包含 'RoleName' 的定义，并且找不到接受类型 'object' 的第一个参数的可访问扩展方法 'RoleName' （您是否缺少 using 指令或程序集引用？）

以下是 Microsoft 创建的 ASP.NET 会员系统中的相关 table。有关完整架构的参考，请参阅：https://docs.microsoft.com/en-us/aspnet/web-forms/overview/older-versions-security/membership/creating-the-membership-schema-in-sql-server-cs

aspnet_UserInRoles

[Index(nameof(RoleId), Name = "aspnet_UsersInRoles_index")]
public partial class aspnet_UsersInRoles
{
    [Key]
    public Guid UserId { get; set; }
    [Key]
    public Guid RoleId { get; set; }

    [ForeignKey(nameof(RoleId))]
    [InverseProperty(nameof(aspnet_Roles.aspnet_UsersInRoles))]
    public virtual aspnet_Roles Role { get; set; }
    [ForeignKey(nameof(UserId))]
    [InverseProperty(nameof(aspnet_Users.aspnet_UsersInRoles))]
    public virtual aspnet_Users User { get; set; }
}

aspnet_Roles

public partial class aspnet_Roles
{
    public aspnet_Roles()
    {
        aspnet_UsersInRoles = new HashSet<aspnet_UsersInRoles>();
    }

    public Guid ApplicationId { get; set; }
    [Key]
    public Guid RoleId { get; set; }
    [Required]
    [StringLength(256)]
    public string RoleName { get; set; }
    [Required]
    [StringLength(256)]
    public string LoweredRoleName { get; set; }
    [StringLength(256)]
    public string Description { get; set; }

    [ForeignKey(nameof(ApplicationId))]
    [InverseProperty(nameof(aspnet_Applications.aspnet_Roles))]
    public virtual aspnet_Applications Application { get; set; }
    [InverseProperty("Role")]
    public virtual ICollection<aspnet_UsersInRoles> aspnet_UsersInRoles { get; set; }
}

aspnet_Users

[Index(nameof(ApplicationId), nameof(LastActivityDate), Name = "aspnet_Users_Index2")]
public partial class aspnet_Users
{
    public aspnet_Users()
    {
        Users = new HashSet<Users>();
        aspnet_PersonalizationPerUser = new HashSet<aspnet_PersonalizationPerUser>();
        aspnet_UsersInRoles = new HashSet<aspnet_UsersInRoles>();
    }

    public Guid ApplicationId { get; set; }
    [Key]
    public Guid UserId { get; set; }
    [Required]
    [StringLength(256)]
    public string UserName { get; set; }
    [Required]
    [StringLength(256)]
    public string LoweredUserName { get; set; }
    [StringLength(16)]
    public string MobileAlias { get; set; }
    public bool IsAnonymous { get; set; }
    [Column(TypeName = "datetime")]
    public DateTime LastActivityDate { get; set; }

    [ForeignKey(nameof(ApplicationId))]
    [InverseProperty(nameof(aspnet_Applications.aspnet_Users))]
    public virtual aspnet_Applications Application { get; set; }
    [InverseProperty("User")]
    public virtual aspnet_Membership aspnet_Membership { get; set; }
    [InverseProperty("User")]
    public virtual aspnet_Profile aspnet_Profile { get; set; }
    [InverseProperty("aspUser")]
    public virtual ICollection<Users> Users { get; set; }
    [InverseProperty("User")]
    public virtual ICollection<aspnet_PersonalizationPerUser> aspnet_PersonalizationPerUser { get; set; }
    [InverseProperty("User")]
    public virtual ICollection<aspnet_UsersInRoles> aspnet_UsersInRoles { get; set; }
}

Answer 1

如果我是你，我会这样写这个查询：

var result = context.UserRoles
                    .Where(x => x.UserId == ID_TO_SEARCH)
                    .Join(
                        context.Roles,
                        ur => ur.RoleId,
                        r => r.Id,
                        (ur, role) => new
                        {
                            ur,
                            role
                        }
                    )
                    .Select(x => x.role.Name)
                    .FirstOrDefault();

这产生的查询，对我来说，完全没问题而且更优雅：

SELECT TOP(1) [a0].[Name]
FROM [AspNetUserRoles] AS [a]
INNER JOIN [AspNetRoles] AS [a0] ON [a].[RoleId] = [a0].[Id]
WHERE [a].[UserId] = N''

更新：

如果我理解正确，我在评论中被问到什么，那么这个查询将 select 角色名称 LIKE LEFT JOIN:

var rolesQuery = context.UserRoles
                         .Join(
                            context.Roles,
                            ur => ur.RoleId,
                            r => r.Id,
                            (ur, r) => new
                            {
                                ur,
                                r
                            }
                        );
                    
    var result = context.Users
                        .Where(x => x.Id == "")
                        .Select(u => new
                        {
                           Name = u.UserName,
                           Role = rolesQuery
                               .Where(sub=> sub.ur.UserId == u.Id)
                               .Select(sub=> sub.r.Name)
                               .FirstOrDefault()
                        })
                        .FirstOrDefault();

这导致此 SQL 语句：

      SELECT TOP(1) [a1].[UserName] AS [Name], (
          SELECT TOP(1) [a0].[Name]
          FROM [AspNetUserRoles] AS [a]
          INNER JOIN [AspNetRoles] AS [a0] ON [a].[RoleId] = [a0].[Id]
          WHERE [a].[UserId] = [a1].[Id]) AS [Role]
      FROM [AspNetUsers] AS [a1]
      WHERE [a1].[Id] = N''

如您所见，没有 LEFT JOIN，但是 sub-select 将以与 LEFT JOIN 类似的方式 return 数据。不幸的是，基于 lambda 的查询不支持完整的 LEFT JOIN 并且编写真正的 LEFT JOIN 的唯一选项可以通过 SQL-like IQueryable.

来丰富

我在 EF core 5 lib 中看到一个名为 LeftJoin() 的方法，但它抛出 NotImplementedException。我认为它会在稍后发布

Answer 2

如果您只需要特定用户的角色名称，则应简化查询：

var query = 
   from r in this.DbContext.aspnet_Users
   where r.UserId == dpass.UserId
   from ro in r.aspnet_Roles
   select ro.RoleName;

Entity Framework Core 5.0 如何将 LINQ 转换为多对多连接以使用交集 table 作为 ASP.NET 成员资格

Entity Framework Core 5.0 How to convert LINQ for many-to-many join to use Intersection table for ASP.NET Membership

c#

linq

sql-server

entity-framework-6

entity-framework-core