如何检索使用MongoDB的官方C＃驱动程序的所有嵌入文档的价值？

问题描述

给定以下类和示例文档，如何从问题集合中检索AnswerChoice文档，其中_id在AnswerChoice是'4d6d336ae0f84c23bc1fae00'使用官方的C＃驱动程序。谢谢。

Given the the following classes and sample document, How do I retrieve a AnswerChoice document from the Question collection where _id in AnswerChoice is '4d6d336ae0f84c23bc1fae00' using the official C# driver. Thank you.

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
    }
}

//代码检索具有_id为4d6d336ae0f84c23bc1fae00的AnswerChoice的问题

//Code to retrieve Question that have AnswerChoice with _id of "4d6d336ae0f84c23bc1fae00"

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);
}

//如何使用_id4d6d336ae0f84c23bc1fae00检索AnswerChoice对象？

//How do I retrieve an AnswerChoice object with _id of "4d6d336ae0f84c23bc1fae00" ?????

推荐答案

您应该加载问题（如上面的代码），并使用linq或foreach获取指定的_ID。因此代码如下：

You should load question(as in code above) and use linq or foreach to get answer item with specified _id. So code will looks like:

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);
}

我建议而不是Find使用FindOne方法只有一个回答与上面指定的_id存在）。

Also i suggest instead of Find use FindOne method(because i suppose that you sure that only one answer with above specified _id exists).

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