如何使用MongoDB官方C＃驅動程序檢索所有嵌入文檔值？

Question

鑑於以下類別和示例文檔，如何從Question集合中找到AnswerChoice文檔，其中AnswerChoice中的_id是使用官方C＃驅動程序的「4d6d336ae0f84c23bc1fae00」。謝謝。

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;} 

} 

//樣品文件

{ 
    "_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 
    } 
} 

//代碼檢索問題有AnswerChoice與_id 「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); 
} 

//如何檢索AnswerChoice物體「4d6d336ae0f84c23bc1fae00」的_id

Answer 1

您應該加載問題（如上面的代碼中所示）並使用linq或foreach來獲取具有指定_id的回答項目。所以，代碼將是這樣的：

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); 
} 

此外，我建議，而不是尋找使用FindOne方法（因爲我想你肯定只有一個答案用上面指定_id存在）。

Answer 2

看起來你只想要子文檔而不是整個文檔。 Mongodb目前不支持此功能。在匹配中，整個文檔被返回。您的查詢與Filtering embedded documents in MongoDB類似。 這個功能請求有一個開放的JIRA項目，你應該投票http://jira.mongodb.org/browse/SERVER-828