在MongoDB中,如何搜索子文档数组？

Question

我在mongodb有一份调查文件,每项调查都有surveyRefId独特的鉴定.我无法理解如何在surveyRefid = 377或360的文档中查找具有questionType = hard的子文档.

这是一个示例文档:

{
  "json": {
    "surveyRefId": 377,
    "surveyName": "survey on sociology",
    "questionsVoList": [
      {
        "questionId": "556708425215763c64b8af3d",
        "questionText": "question no 1",
        "questionTitle": "",
        "questionType": "hard",
        "preQuestion": true,
        "questionOptions": [
          {
            "questionRefId": 0,
            "optionType": "RADIOBUTTON",
            "isanswer": true,
            "optionText": "ch1"
          }
        ]
      },
      {
        "questionId": "556708425215763c64b8af3d",
        "questionText": "question no 2",
        "questionTitle": "",
        "questionType": "simple",
        "question": true,
        "questionOptions": [
          {
            "questionRefId": 0,
            "optionType": "RADIOBUTTON",
            "isanswer": true,
            "optionText": "ch1"
          }
        ],
      },
      {
       "questionId": "556708425215763c64b8af3d",
        "questionText": "question no 3",
        "questionTitle": "",
        "questionType": "hard",
        "questionOptions": [
          {
            "questionRefId": 0,
            "optionType": "RADIOBUTTON",
            "isanswer": true,
            "optionText": "ch1"
          },
          {
            "questionRefId": 0,
            "optionType": "RADIOBUTTON",
            "isanswer": false,
            "optionText": "ch2"
          }
        ],
       }
    ]
  }
}

编辑 -根据Sylvain Leroux使用Java驱动程序解决方案

    BasicDBObject matchSurvey = new BasicDBObject();
    matchSurvey.put("$match", new BasicDBObject("json.surveyRefId", new BasicDBObject("$in", new Integer[]{377,360})));
    BasicDBObject unwind = new BasicDBObject();
    unwind.put("$unwind", "$json.questionsVoList");
    BasicDBObject matchQuestion = new BasicDBObject();
    matchQuestion.put("$match", new BasicDBObject("json.questionsVoList.questionType", "hard"));
    HashMap map = new HashMap();
    map.put("_id", "$_id");
    map.put("questionsVoList", new BasicDBObject("$push", "$json.questionsVoList"));
    BasicDBObject group = new BasicDBObject();
    group.put("$group",map);        
    List<BasicDBObject> list = new ArrayList<BasicDBObject>();
    list.add(matchSurvey);
    list.add(unwind);
    list.add(matchQuestion);
    list.add(group);
    AggregateIterable output = collection.aggregate(list, DBObject.class);

Answer 1

"查找具有questionType = "hard""的子文档可以通过三种不同的方式理解:

所有文档都有"硬"查询

如果您只想要所有文档都有"硬查询",您将使用find和$elemMatch:

db.test.find({"json.surveyRefId": { $in: [377, 360]},
              "json.questionsVoList": {$elemMatch: {"questionType":"hard"}}})

首先对文档进行"硬"查询

如果需要查找文档的第一个 "硬"查询,则将上述查询与$投影运算符组合:

db.test.find({"json.surveyRefId": { $in: [377, 360]}, 
              "json.questionsVoList": {$elemMatch: {"questionType":"hard"}}}
             {"json.surveyRefId":1, "json.questionsVoList.$":1})

所有硬查询

如果您需要查找文档的所有 "硬"查询,则必须使用聚合框架:

db.test.aggregate({$match: { "json.surveyRefId": { $in: [377, 360]} }},
                  {$unwind: "$json.questionsVoList"},
                  {$match: { "json.questionsVoList.questionType": "hard"}},
                  {$group: {_id: "$_id", questionsVoList: {$push: "$json.questionsVoList"}}}
)

• 第一个$match步骤将根据过滤掉不需要的文件surveyRefId
• 然后$unwind将为每个子文档生成一个文档
• 另一个$match过滤掉基于的不需要的文档questionType
• 最后,a $group将所有子文档合并为一个给定的子文档_id

生产:

{
    "_id" : ObjectId("556828d002509ae174742d11"),
    "questionsVoList" : [
        {
            "questionId" : "556708425215763c64b8af3d",
            "questionText" : "question no 1",
            "questionTitle" : "",
            "questionType" : "hard",
            "preQuestion" : true,
            "questionOptions" : [
                {
                    "questionRefId" : 0,
                    "optionType" : "RADIOBUTTON",
                    "isanswer" : true,
                    "optionText" : "ch1"
                }
            ]
        },
        {
            "questionId" : "556708425215763c64b8af3d",
            "questionText" : "question no 3",
            "questionTitle" : "",
            "questionType" : "hard",
            "questionOptions" : [
                {
                    "questionRefId" : 0,
                    "optionType" : "RADIOBUTTON",
                    "isanswer" : true,
                    "optionText" : "ch1"
                },
                {
                    "questionRefId" : 0,
                    "optionType" : "RADIOBUTTON",
                    "isanswer" : false,
                    "optionText" : "ch2"
                }
            ]
        }
    ]
}