How to select from field name from nested arrays in mongodb?

Question

I have a document with nested arrays and I can't work out how to select the from the a field.

I'd like to select all documents where "components" has a "mast".

I've tried.

db.sites.find({"components": "mast" } ).pretty();

db.sites.find({"components.$": "mast" } ).pretty();

db.sites.find({"components.$.$": "mast" } ).pretty();

db.sites.find({"components.$.$.mast": {$exists: true} } ).pretty();

db.sites.find({"components.$.mast": {$exists: true} } ).pretty();

db.sites.find({"components.mast": {$exists: true} } ).pretty();

and a bunch of other failed attempts.

{
    "_id" : ObjectId("23456yujbvfdfg"),
    "d": 1234567,
    "components" : [
        [
            "mast",
            {
                "foo":"bar"
            }
        ],
        [
            "commsbox",
            {
                "BLARN": "bAAA"
            }
        ]
    ]
}

My attempts are only returning blank results.

What if components was an array of objects? Your queries are expecting that. Seems like a data modelling error to me. — HIRA THAKUR
– HIRA THAKUR, Commented Feb 15, 2019 at 11:46

HIRA THAKUR · Accepted Answer · 2019-02-15 12:24:11Z

2

You can use $elemMatch

db.sites.find(
   { "components": { $elemMatch:  { $elemMatch:  {$eq:"mast"}  } }}
)

edited Feb 15, 2019 at 12:24

answered Feb 15, 2019 at 12:17

HIRA THAKUR

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DHIRAJ KATEKAR · Accepted Answer · 2019-02-15 12:37:04Z

1

If you are maintaining components as array then you query should look like

db.test.find({ "components": { $elemMatch:  { $elemMatch:  {$eq:"mast"}  } }})

I have posted the solution based on the schema you have shared but i am certain that schema needs to be changed

edited Feb 15, 2019 at 12:37

answered Feb 15, 2019 at 12:31

DHIRAJ KATEKAR

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1 Comment

psykx Over a year ago

I have changed the schema as I was too confusing.

Abdelrahman Hossam · Accepted Answer · 2019-02-15 12:22:12Z

1

this should work

db.sites.find({
    "components": {
            $elemMatch: {
                $elemMatch: { $in: ['mast'] }
            }
    } 
})

answered Feb 15, 2019 at 12:22

Abdelrahman Hossam

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