在MongoDB中如何查询count number of 2 equal field？

Question

我的调查结果 (name=surveyresults) 在 MongoDB 中有一个 collection。我想要一个查询，根据类别给我正确答案的数量，例如，类别 "Bee" 正确答案的数量 10。我尝试了不同的方法，但这些不是我想要的结果。我已经搜索并发现这个 post Group count with MongoDB using aggregation framework 有用但不适合我。

这是我 surveyResults collection 中的部分数据：

[{"_id":"0eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJfaWQiOjE5LCJpYXQiOjE1MjQwMDgzOTl9.2YvhnXtCD7-fm4B14k10m6NF7xuv7moCTbekVekkbvY","category":"Wasp","photo":"A_wasp_565","description":"","answer":"Bee","__v":0},{"_id":"1eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJfaWQiOjE5LCJpYXQiOjE1MjQwMDgzOTl9.2YvhnXtCD7-fm4B14k10m6NF7xuv7moCTbekVekkbvY","category":"Wasp","photo":"A_Pompilid_wasp_007","description":"","answer":"Wasp","__v":0},{"_id":"2eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJfaWQiOjE5LCJpYXQiOjE1MjQwMDgzOTl9.2YvhnXtCD7-fm4B14k10m6NF7xuv7moCTbekVekkbvY","category":"Wasp","photo":"wasp_248","description":"","answer":"Wasp","__v":0},{"_id":"3eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJfaWQiOjE5LCJpYXQiOjE1MjQwMDgzOTl9.2YvhnXtCD7-fm4B14k10m6NF7xuv7moCTbekVekkbvY","category":"Fly","photo":"A_butterfly_291","description":"kjlkjlkjlk","answer":"Moth/Butterfly","__v":0},

我想要这样的结果:

[{"category":"Fly","count":3, "correct":1},{"category":"Wasp","count":3, "correct":1},{"category":"Moth/Butterfly","count":4, "correct":2},{"category":"Bee","count":3, "correct":1}]

现在我有这两个查询但没有给我正确的结果：

1.

SurveyResults.aggregate([
    { $group: {
        _id: { answer: '$answer', category: '$category' }
    }},
    { $group: {
        _id: '$_id.answer',
        answer_correct: { $sum: 1 }
    }},
    { $project: {
        _id: 0,
        answer: '$_id',
        answer_correct: 1
    }}
]).exec(callback);

2.

SurveyResults.aggregate([
    {
    $group:{
        _id:"$answer",
        count: { $sum : {$cond : { if: { $eq: ["answer", "$category"]}, then: 1, else: 0} }}
    }
}]).exec(callback);

此外，我可以通过此查询获得基于类别的答案数量：

SurveyResults.aggregate([
    {
    $group:{
        _id:"$answer",
        count: { $sum : 1 }
    }
}]).exec(callback);

结果：

[{"_id":"Don't know","count":2},{"_id":"Fly","count":3},{"_id":"Wasp","count":3},{"_id":"Moth/Butterfly","count":4},{"_id":"Bee","count":3}]

Answer 1

这是你想要的：

SurveyResults.aggregate([
    $group: {
        _id: "$category",
        "count": { $sum: 1 }, // simply count all questions per category
        "correct": {
            $sum: { // and sum up the correct ones in a field called "correct"
                $cond: [ // ...where "correct ones" means
                    { $eq: [ "$category", "$answer" ] }, // that "category" needs to match "answer"
                    1,
                    0
                ]
            }
        }
    }
}, {
    $project: { // this is just to effectively rename the "_id" field into "category" - may or may not be needed
        _id: 0,
        "category": "$_id",
        "count": "$count",
        "correct": "$correct"
    }
}]).exec(callback);

在MongoDB中如何查询count number of 2 equal field？

How can query in MongoDB that count number of 2 equal field?

grouping

conditional

count

mongodb

nosql