用于连接多个表并在单行中获取逗号分隔值的 LINQ 查询

我有下表的值。

Account:

Role:

账户角色：

现在我想写一个 linq 以获得如下结果：

用户帐号

为了获得上述结果，我在 LINQ 中编写了以下查询。但它没有得到预期的结果。

var userAccount1 = (from account in _db.Accounts
                               join accountRole in _db.AccountRoles on account.Id equals accountRole.AccountId
                               join role in _db.Roles on accountRole.RoleId equals role.Id             
                               select new UserAccountInfo
                               {
                                   AccountId = account.Id,
                                   Name = account.UserFullName,
                                   Email = account.Email,                                 
                                   Roles = string.Join(",", role.Title)
                               });

我终于找到了答案。可以通过不同的方式实现结果。举例如下：

var answer1 = (from account in userAccounts
    join accountRole in accountRoles on account.Id equals accountRole.AccountId
    join role in roles on accountRole.RoleId equals role.Id
    select new UserAccount
    {
        AccountId = account.Id,
        Name = account.Name,
        Email = account.Email,
        Roles = role.Title
    }).ToList().GroupBy(x => new { x.AccountId, x.Name, x.Email }).Select(y => new UserAccount
    {
        AccountId = y.Key.AccountId,
        Name = y.Key.Name,
        Email = y.Key.Email,
        Roles = string.Join(", ", y.Select(a => a.Roles))
    }).ToList();
----------------------------------------------------------------------------
var answer2 = (from account in userAccounts
     join accountRole in accountRoles on account.Id equals accountRole.AccountId
     join role in roles on accountRole.RoleId equals role.Id
     group new { account, role } by new { account.Id, account.Name, account.Email } into ag
     select new UserAccount
     {
         AccountId = ag.Key.Id,
         Name = ag.Key.Name,
         Email = ag.Key.Email,
         Roles = string.Join(", ", ag.Select(x=> x.role.Title))
     }).ToList();
    ----------------------------------------------------------------------------

var answer3 = (from account in userAccounts
     let roles1 = from accountRole in accountRoles
                  join role in roles on accountRole.RoleId equals role.Id
                  where accountRole.AccountId == account.Id
                  select role
     select new UserAccount
     {
         AccountId = account.Id,
         Name = account.Name,
         Email = account.Email,
         Roles = string.Join(", ", roles1.Select(x => x.Title))
     }).ToList();