join 将执行内部联接，因此如果没有 Transfer 或者 TransferProjects 你会得到一张空名单。你需要执行左外连接。类似这样的内容（不确定它是否可以编译，但您应该了解它的要点）：

var result = (from h in context.Accounts
                      join tl in context.Transfers on h.HesapId equals tl.RecipientAccountId into tlG
                      from t in tlG.DefaultIfEmpty()
                      join tpl in context.TransferProjects on t.TransferId equals tpl.TransferId into tplG
                      from tp in tplG.DefaultIfEmpty()
                      join u in context.Users on h.UserId equals u.Id
                      join pl in context.Projects on tp.ProjeId equals pl.ProjeId into plG
                      from p in plG.DefaultIfEmpty()
                      where h.UserId == userId
                      select new TransferListDto()
                      {
                          TransferId = t.TransferId,
                          UserId = u.Id,
                          NameSurname = u.Name + " " + u.Surname,
                          RecipientAccountId = t.RecipientAccountId,
                          SenderAccountId = t.SenderAccountId ,
                          ProjectEnum = t.ProjectEnum,
                          ProjeId = tp.ProjeId,
                          ProjeName = p.Name,
                          Date = t.Date,
                          Amount = t.Amount,

                      }).ToList();

我有一个新问题，用户应该能够看到他/她发送的传输和他/她收到的传输。
那么，我怎样才能为context.transfers表连接条件创建这样的多重连接条件呢？

h.AccountId equals t.RecipientAccountId or h.AccountId equals t.SenderAccountId

下面的代码只显示收件人的转账列表，我希望用户在她/他发送的转账中显示。

var result = (from h in context.Account
                      join t in context.Transfers on h.AccountId equals t.RecipientAccountId
                      join tp in context.TransferProjects on t.TransferId equals tp.TransferId into tpo
                      from tp in tpo.DefaultIfEmpty()
                      join p in context.Projects on tp.ProjeId equals p.ProjeId into po
                      from p in po.DefaultIfEmpty()
                      join u in context.Users on h.UserId equals u.Id
                      join hg in context.Accounts on t.SenderAcctountId equals hg.AccountId
                      join ug in context.Users on hg.UserId equals ug.Id
                      where h.UserId == userId && (startDay != null && endDay != null ? (t.Date >= startDay && t.Date <= endDay) : (t.Date >= last30))
                      select new TransferListDto()
                      {
                          TransferId = t.TransferId,
                          RecipientUserId = u.Id,
                          RecipientNameSurname = u.Name + " " + u.Surname,
                          RecipientAccountId = t.RecipientAccountId,
                          RecipientIban = h.Iban,
                          SenderAdSoyad = ug.Ad + " " + ug.Soyad,
                          SenderUserId = ug.Id,
                          SenderAccountId = t.SenderAccountId,
                          SenderIban = hg.Iban,
                          ProjectEnum = t.ProjeEnum,
                          ProjeId = tp.ProjeId,
                          ProjeName = p.Name,
                          Desc = t.Desc,
                          Date = t.Date,
                          Amount = t.Amount,
                          Status = t.Status

                      }).OrderByDescending(x => x.Date).ToList();