Question

我需要从会话中获取（例如，2），2条消息

我不关心我的列表是什么样的，但我只想要来自id 1的2条消息，来自id2的2条消息，然后继续

示例：

id = idConversation

Id | MessageId | Message
---|-----------|--------
1  | 1         | "asd"
1  | 2         | "asd2"
1  | 3         | "asd3"
1  | 4         | "asd4"
2  | 5         | "asd5"
3  | 6         | "asd6"
3  | 7         | "asd7"
3  | 8         | "asd8"
3  | 9         | "asd9"
3  | 10        | "asd10"
4  | 11        | "asd11"
4  | 12        | "asd12"
4  | 13        | "asd13"

我想要那个

Id   MessageId   Message
---|-----------|--------
1  | 1         | "asd"
1  | 2         | "asd2"
2  | 5         | "asd5"
3  | 6         | "asd6"
3  | 7         | "asd7"
4  | 11        | "asd11"
4  | 12        | "asd12"

我可以通过idConversation，但是我不能在对话中使用grouby来限制数量。

var test = unitOfWork.ChatMensagemRepository.GetAll()
              .Where(x => x.PessoaCodigoPessoa == codigoRemetente)
              .GroupBy(x => x.ChatConversaCodigoChatConversa)
              .Select(group => new
              {
                  codigoChat = group.Key,
                  list = group.Select(mensagem => new
                  {
                      // do stuff
                  })
              }).ToList();

这没关系......但是当我做group.take（2）时，不要限制我的列表。选择.....给我＆＃34;子查询返回超过1行＆＃34;

var test = unitOfWork.ChatMensagemRepository.GetAll()
              .Where(x => x.PessoaCodigoPessoa == codigoRemetente)
              .GroupBy(x => x.ChatConversaCodigoChatConversa)
              .Select(group => new
              {
                  codigoChat = group.Key,
                  list = group.Take(2).Select(mensagem => new
                  {
                      // do stuff
                  })
              }).ToList();

错误：子查询返回的行数超过1行

var test = unitOfWork.ChatMensagemRepository.GetAll()
              .Where(x => x.PessoaCodigoPessoa == codigoRemetente)
              .GroupBy(x => x.ChatConversaCodigoChatConversa)
              .Select(group => new
              {
                  codigoChat = group.Key,
                  list = group.Select(mensagem => new
                  {
                      // do stuff
                  }).take(2)
              }).ToList();

错误：子查询返回的行数超过1行

Answer 1

导致这种情况，因为MySQL或服务器本身的EF提供程序无法将此linq转换为SQL，因此您应首先从服务器获取数据，然后再将其与Take(2)分组：

var test = unitOfWork.ChatMensagemRepository.GetAll()
              .Where(x => x.PessoaCodigoPessoa == codigoRemetente)
              //this section is added
              .Select(x => new 
              {
                  x.ChatConversaCodigoChatConversa,
                  x.prop1,//specify only columns, which you need for below code with Take
                  x.prop2
              }).ToList()
              //end of section
              .GroupBy(x => x.ChatConversaCodigoChatConversa)
              .Select(group => new
              {
                  codigoChat = group.Key,
                  list = group.Take(2).Select(mensagem => new
                  {
                     mensagem.prop1, 
                     mensagem.prop2
                  }).ToList()
              }).ToList();

在Entity Framework中的Groupby中获取（限制）列表

1 个答案: