Question

我有一个变量var correctAnswers;

在我的MongoDB中，我有以下文档（如下）。我正在尝试编写一个查询，它从“测验”字段中获取所有“正确”字段并将它们放入自己的数组中，因此我可以将该数组设置为var correctAnswers;。

"title" : "Economics questions"
"quiz": "[{
          "question": "Which of these involves the analysis of of a business's financial statements, often used in stock valuation?",
          "choices": ["Fundamental analysis", "Technical analysis"],
          "correct": 0
        }, {
          "question": "What was the name of the bond purchasing program started by the U.S. Federal Reserve in response to the 2008 financial crisis?",
          "choices": ["Stimulus Package", "Mercantilism", "Quantitative Easing"],
          "correct": 2
        }, {
          "question": "Which term describes a debt security issued by a government, company, or other entity?",
          "choices": ["Bond", "Stock", "Mutual fund"],
          "correct": 0
        }, {
          "question": "Which of these companies has the largest market capitalization (as of October 2015)?",
          "choices": ["Microsoft", "General Electric", "Apple", "Bank of America"],
          "correct": 2
        }, {
          "question": "Which of these is a measure of the size of an economy?",
          "choices": ["Unemployment rate", "Purchasing power index", "Gross Domestic Product"],
          "correct": 2
        }]"

我应该怎么做，或者有人指出我正确的方向？我尝试过预测，但是我应该进行聚合吗？谢谢你的帮助。

为了清晰起见编辑：我在这个例子中寻找的输出是一个数组，[0,2,0,2,2]

Answer 1

你可以得到这个结果 [{correct：0}，{correct：2}，{correct：0}，{correct：2}]但是[0,2,0,2,2]类型的结果是不可能的，除非我们使用distinct

db.quiz.aggregate（ //初始文档匹配（使用索引，如果有合适的文档） {$ match：{ “标题”：“经济学问题” }}，
// Convert embedded array into stream of documents
{ $unwind: '$quiz' },

    },

// Note: Could add a `$group` by _id here if multiple matches are expected

// Final projection: exclude fields with 0, include fields with 1
{ $project: {
    _id: 0,
    score: "$quiz.correct"
}} )

Answer 2

db.users.find( { }, { "quiz.correct": 1,"_id":0 } )

//上面的查询将返回以下输出：

{
        "quiz" : [
                {
                        "correct" : 0
                },
                {
                        "correct" : 2
                },
                {
                        "correct" : 0
                },
                {
                        "correct" : 2
                },
                {
                        "correct" : 2
                }
        ]
}

根据节点js中的要求处理此输出。

Answer 3

通过聚合实现这一目标的一种方法

db.collectionName.aggregate([
     // use index key in match pipeline,just for e.g using title here
    { $match: { "title" : "Economics questions" }},
    { $unwind: "$quiz" },
    { $group: {
          _id:null,
          quiz: { $push:  "$quiz.correct" }
        } 
    },
    //this is not required, use projection only if you want to exclude/include fields 
    { 
        $project: {_id: 0, quiz: 1}
    } 
])

以上查询将为您提供以下输出

{
    "quiz" : [ 0, 2, 0, 2, 2 ]
}

然后根据需要简单处理此输出。

Answer 4

试试这个：

db.getCollection('quize').aggregate([
{$match:{_id: id }},
{$unwind:'$quiz'}, 
{$group:{
_id:null, 
score: {$push:"$quiz.correct"} 
}}
])

它会给你预期的输出。

如何将MongoDB查询中的嵌入式文档拉入数组？

4 个答案: