how to find empty use mongodb?

Question

I want to find out from the database by:

db.xx.find({"fields.name.sourceTexts":null})

or

db.xx.find({"fields.name.sourceTexts":""})

but it not work and find all

[
    {
        "_id": "5b432195e28b99127c59161e",
        "fields": {
            "img": {
                "sourceTexts": [],
                "_class": "us.codecraft.webmagic.selector.PlainText"
            },
            "name": {
                "sourceTexts": [],
                "_class": "us.codecraft.webmagic.selector.PlainText"
            },
            "old": {
                "sourceTexts": [],
                "_class": "us.codecraft.webmagic.selector.PlainText"
            },
            "post": {
                "sourceTexts": [],
                "_class": "us.codecraft.webmagic.selector.PlainText"
            },
            "focusTieba": [],
            "visitor": {
                "sum": 0,
                "list": []
            },
            "follow": {
                "sum": 0,
                "list": []
            },
            "fans": {
                "sum": 0,
                "list": []
            }
        },
        "request": {
            "url": "http://tieba.baidu.com/home/main?un=%DB%A2%D4%B495",
            "cookies": {},
            "headers": {},
            "priority": 0,
            "binaryContent": false
        },
        "skip": false,
        "_class": "us.codecraft.webmagic.ResultItems"
    }
]

score 0 · Answer 1 · answered Jul 10 '18 at 06:40

0

If I got what you need, I think you are in need of next query

db.xx.find({"fields.name.sourceTexts":[]})

answered Jul 10 '18 at 06:40

damirljub

307
2
9

thank answer , now i want delete {fields.name.sourceTexts:[]} , but i cant find by {fields.name.sourceTexts:[]} – funbean Jul 10 '18 at 06:46
You can find it but what you need is to delete by its MongoId. And you should use findOne(). https://docs.mongodb.com/manual/reference/method/db.collection.findOne/ – damirljub Jul 10 '18 at 07:05
but result has many , i want like sql `select * from table where name is null` like this – funbean Jul 10 '18 at 07:15

score 0 · Accepted Answer · answered Jul 10 '18 at 07:06

0

You can use $exists operator to check if field exists and $size operator to check if array is empty.

db.xx.find( { "fields.name.sourceTexts" : { $exists:true, $size:0 } } )

answered Jul 10 '18 at 07:06

Manish Sharma

31
1

thank very much, Is the result I want – funbean Jul 10 '18 at 07:19

how to find empty use mongodb?

2 Answers2