如何使用MongoDB和C#驱动程序查询子文档集合

Question

我有以下结构:

public class ThreadDocument
{
    public ThreadDocument()
    {
        Messages = new List<Message>();
        Recipients = new List<Recipient>();
    }

    [JsonIgnore]
    public ObjectId Id { get; set; }
    public IList<Recipient> Recipients { get; set; }
    public IList<Message> Messages { get; set; }
    public DateTime LastMessageSent { get; set; }
    public string LastSentByUserName { get; set; }
    public string LastSentAvatarUrl { get; set; }
    public string Snippet { get; set; }
    public int MessageCount { get; set; }

}

public class Recipient
{
    public string UserId { get; set; }
    public int Status { get; set; }
}

public class Message
{
    public string FromUserId { get; set; }
    public string FromUsername { get; set; }
    public string FromAvatarUrl { get; set; }
    public DateTime Sent { get; set; }
    public string Text { get; set; }
}

当我保存时,它产生这样的东西:

{
  "_id" : ObjectId("4fa5eab4bfeddf23fcd01e4a"),
  "Recipients" : [{
      "UserId" : "4fa5d4d8bfeddf23fc72e590",
      "Status" : 1
    }, {
      "UserId" : "4fa5d4f9bfeddf23fc72e592",
      "Status" : 0
    }],
  "Messages" : [{
      "FromUserId" : "4fa5d4d8bfeddf23fc72e590",
      "FromUsername" : "a",
      "FromAvatarUrl" : null,
      "Sent" : ISODate("2012-05-06T03:06:28.396Z"),
      "Text" : "b"
    }],
  "LastMessageSent" : ISODate("2012-05-06T03:06:28.395Z"),
  "LastSentByUserName" : "a",
  "LastSentAvatarUrl" : null,
  "Snippet" : "b",
  "MessageCount" : 1
}

我想要做的是,如果已经创建了一个线程,使用相同的线程并根据用户是否向同一用户发送消息而将消息发送到该消息,反之亦然.

我认为这样的东西会起作用,但它返回null(没有值):

var thread = threadHelper.Collection.Find(
    Query.And(Query.EQ("Recipients.UserId", user.Id), Query.EQ("Recipients.UserId", sendToUser.Id))
).SingleOrDefault();

我想是一个包含所有？还是全部？不确定如何进行查询.

Answer 1

试试ElemMatch:

var thread = threadHelper.Collection.Find(
    Query.And(
        Query.ElemMatch("Recipients", Query.EQ("UserId", user.Id)), 
        Query.ElemMatch("Recipients", Query.EQ("UserId", sendToUser.Id))
    )
).SingleOrDefault();