Projection in MongoDB



In MongoDB, projection means selecting only the necessary data rather than 

selecting the whole of the data of a document. If a document has 5 fields and 

you need to show only 3, then select only 3 fields from them.


You may also like MongoDb insert.


1)Projection in find.



Here 0 means not to project i.e exclusion and 1 means project i.e inclusion as per MongoDB.

Projection cannot have a mix of inclusion and exclusion but only the _id field can exclude with inclusion.



db.collection("companies").find({name:"Dvara SmartGold"},{projection: { _id:0,id: 1, name: 1 } }).toArray()



Or



db.collection("companies").find({name:"Dvara SmartGold"}).project({_id:0,id: 1, name: 1}).toArray()



This will give us all documents inside companies collection as per filter with only name and id fields.



2)Projection in findOne.



db.collection("companies").findOne({name:"Dvara SmartGold"},{projection: { _id:0,id: 1, name: 1 } })

//This will give us one document inside companies collection as per filter with only name and id fields.



3)Projection in Arregation.

db.collection('companies').aggregate([

    {

        $match: { 'name': 'Dvara SmartGold' },

    },

    {



        $lookup: {

            from: "partners",

            localField: "id",

            foreignField: "refid",

            as: "partner"

        }

    },

    {

        $project: {

            id: 1,

            name: 1,

            partner: 1

        },

    },



]).toArray();



This will give us documents inside companies collection and also we have join partners collection as per filter with only name, partner, and id fields.


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