如何使用 MongoDB 的官方 C# 驱动程序检索所有嵌入文档值？

Question

给定以下类和示例文档，如何使用官方 C# 驱动程序从 Question 集合中检索 AnswerChoice 文档，其中 AnswerChoice 中的 _id 为“4d6d336ae0f84c23bc1fae00”。谢谢。

public class Question
{
     [BsonId]
     public ObjectId QuestionId
     {get;set;}

     public string Question
     {get;set;}

     public List<AnswerChoice> AnswerChoices
     {get;set;}
}

public class AnswerChoice
{
     [BsonId]
     public ObjectId AnswerChoiceId
     {get;set;}

     public string Answer
     {get;set;}

     public int Order
     {get;set;}

}

// 示例文档

{
  "_id": "4d6d3369e0f84c23bc1facf7",
  "Question": "Question 1",
  "AnswerChoices": [
    {
      "_id": "4d6d3369e0f84c23bc1facf2",
      "Answer": "Answer Choice A",
      "Order": 1
    },
    {
      "_id": "4d6d3369e0f84c23bc1facf3",
      "Answer": "Answer Choice B",
      "Order": 2
    },
    {
      "_id": "4d6d3369e0f84c23bc1facf4",
      "Answer": "Answer Choice C",
      "Order": 3
    },
    {
      "_id": "4d6d3369e0f84c23bc1facf5",
      "Answer": "Answer Choice D",
      "Order": 4
    },
    {
      "_id": "4d6d3369e0f84c23bc1facf6",
      "Answer": "Answer Choice E",
      "Order": 5
    }
}

// 检索 _id 为“4d6d336ae0f84c23bc1fae00”的 AnswerChoice 问题的代码

List<Question> list = new List<Question>();
MongoServer _server = MongoServer.Create("mongodb://localhost");
MongoDatabase _database = _server.GetDatabase("test");
var query = Query.And(Query.EQ("AnswerChoices._id", new ObjectId("4d6d336ae0f84c23bc1fae00")));
MongoCollection<Question> collection = _database.GetCollection<Question>("Question");
MongoCursor<Question> cursor = collection.Find(query);

foreach (var q in cursor)
{
    list.Add(q);
}

//如何检索 _id 为“4d6d336ae0f84c23bc1fae00”的 AnswerChoice 对象??????

Answer 1

您应该加载问题（如上面的代码所示）并使用 linq 或 foreach 来获取具有指定 _id 的答案项目。所以代码看起来像：

List<Question> list = new List<Question>();
MongoServer _server = MongoServer.Create("mongodb://localhost");
MongoDatabase _database = _server.GetDatabase("test");
var query = Query.And(Query.EQ("AnswerChoices._id", new ObjectId("4d6d336ae0f84c23bc1fae00")));
MongoCollection<Question> collection = _database.GetCollection<Question>("Question");
MongoCursor<Question> cursor = collection.Find(query);

var id = new ObjectId("4d6d336ae0f84c23bc1fae00");
foreach (var q in cursor)
{
    var answerChoice = q.AnswerChoices.Single(x=> x.AnswerChoiceId == id);
    list.Add(q);
}

另外，我建议使用 FindOne 方法代替 Find（因为我认为您确定只有一个具有上述指定 _id 的答案存在）。

Answer 2

看起来您只需要子文档而不是整个文档。 Mongodb 目前不支持此功能。在匹配时，将返回整个文档。您的查询类似于过滤 MongoDB 中的嵌入文档。
此功能请求有一个开放的 JIRA 项目，您应该对其进行投票 http://jira.mongodb .org/browse/SERVER-828