mongodb - mongo complex query problem

Question

Original json

{
    "_id" : ObjectId("58b3a8dc96fbc7cfb8287093"),
    "name" : "《地下水质量标准》",
    "GBNumber" : "GB/T 14848-93",
    "dataEntryClerk" : "handsomeboy",
    "lastModified" : "Fri Feb 27 2017 12:03:40 GMT+0800",
    "contents" : [ 
        {
            "standardID" : "9527-01",
            "unit" : "mg/L",
            "classifications" : [ 
                {
                    "level" : "I",
                    "upperLimit" : "0",
                    "lowerLimit" : "50"
                }, 
                {
                    "level" : "II",
                    "upperLimit" : "50",
                    "lowerLimit" : "150"
                }, 
                {
                    "level" : "III",
                    "upperLimit" : "150",
                    "lowerLimit" : "250"
                }, 
                {
                    "level" : "IV",
                    "upperLimit" : "250",
                    "lowerLimit" : "350"
                }, 
                {
                    "level" : "V",
                    "upperLimit" : "350",
                    "lowerLimit" : "-1"
                }
            ]
        }, 
        {
            "standardID" : "7439-89-6",
            "unit" : "mg/L",
            "classifications" : [ 
                {
                    "level" : "I",
                    "upperLimit" : "0",
                    "lowerLimit" : "0.1"
                }, 
                {
                    "level" : "II",
                    "upperLimit" : "0.1",
                    "lowerLimit" : "0.2"
                }, 
                {
                    "level" : "III",
                    "upperLimit" : "0.2",
                    "lowerLimit" : "0.3"
                }, 
                {
                    "level" : "IV",
                    "upperLimit" : "0.3",
                    "lowerLimit" : "0.4"
                }, 
                {
                    "level" : "V",
                    "upperLimit" : "0.5",
                    "lowerLimit" : "-1"
                }
            ]
        }
    ]
}

The results you want to query:

{
    "contents" : [ 
        {
            "standardID" : "9527-01",
            "unit" : "mg/L",
            "classifications" : [ 
                {
                    "level" : "I",
                    "upperLimit" : "0",
                    "lowerLimit" : "50"
                }, 
                {
                    "level" : "II",
                    "upperLimit" : "50",
                    "lowerLimit" : "150"
                }, 
                {
                    "level" : "III",
                    "upperLimit" : "150",
                    "lowerLimit" : "250"
                }, 
                {
                    "level" : "IV",
                    "upperLimit" : "250",
                    "lowerLimit" : "350"
                }, 
                {
                    "level" : "V",
                    "upperLimit" : "350",
                    "lowerLimit" : "-1"
                }
            ]
        }
    ]
}

Could you please tell me how to write db.xxx.find()

Answer 1

First of all, a comment:

Ask a question and post minimizedexamples of reproducibleproblems. If you post such a long document, everyone will be tired of reading it.

---

What you need is actually to return specific documents in the array, not the entire array.

1 If you only need to return one element in the array

db.xxx.find(
    {'contents.standardID': '9527-01'},
    {contents: {$elemMatch: {standardID: '9527-01'}}, _id: 0}
)

The first line is the query condition, and the second line is the filter condition. You can see that operators can also be used in filter conditions. However, this operator will only return the first element that meets the condition, and requires MongoDB version 2.2 or above. Or use the

subscript selector:

db.xxx.find(
    {'contents.standardID': '9527-01'},
    {'contents.$': 1, _id: 0}
)

$The query conditions in the above example can also be used.

$elemMatchIf you need to return multiple matching elements in an array:

2

$unwindUse

to operate contents as an independent document stream. For the code, see @bguo's answer.

But if your array is large, this can cause performance issues. $unwind来把contents
3

$filterThis is a new operator in the

version, used to filter the returned content.

db.xxx.aggregate(
    {$match: {'contents.standardID': '9527-01'}},
    {$project: {
        contents: {$filter: {
            input: '$contents',
            as: 'contents',
            cond: {$eq: ['$$contents.standardID', '9527-01']}
        }},
        _id: 0
    }}
)

3.2Of course you can also use and many other methods.

Answer 2

Query conditions. For example name

db.xxx.find({"name" : "《地下水质量标准》" } ,function(err, data){ 
    if(data){
        console.log(data.contents)
    }
})

Answer 3

One way to implement it: Use MongoDB’s Aggregate.

1. First apply $unwind to the contents containing array

2. Then use $match to apply filtering conditions

3. Finally, use $project to retain the required fields

Refer to the code below

 db.test1.aggregate([
                    {$unwind : "$contents"},
                    {$match : { name :  "《地下水质量标准》", "contents.standardID" :  "9527-01"}},
                    { $project : { contents : 1 , _id : 0 }}
                    ])

For reference.

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Answer 4

db.xxx.find({"contents.standardID": "9527-01"}, {contents: 1})

_id字段会自动输出，就忽略吧