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How to project specific elements in an array field with MongoDB?
To project-specific elements in an array field, use $project. Let us create a collection with documents −
>db.demo355.insertOne({"id":101,"details":[{"Name":"Chris",isMarried:1},{"Name":"David",isMarried:0},{"Name":"Mike",isMarried:1}]}); { "acknowledged" : true, "insertedId" : ObjectId("5e568928f8647eb59e5620c5") }
Display all documents from a collection with the help of find() method −
> db.demo355.find().pretty();
This will produce the following output −
{ "_id" : ObjectId("5e568928f8647eb59e5620c5"), "id" : 101, "details" : [ { "Name" : "Chris", "isMarried" : 1 }, { "Name" : "David", "isMarried" : 0 }, { "Name" : "Mike", "isMarried" : 1 } ] }
Following is the query to project-specific elements in an array field −
> db.demo355.aggregate([ ... { ... $project: { ... details: { ... $filter: { ... input: "$details", ... as: "out", ... cond: { $eq:["$$out.isMarried",1] } ... } ... } ... } ... } ... ])
This will produce the following output −
{ "_id" : ObjectId("5e568928f8647eb59e5620c5"), "details" : [ { "Name" : "Chris", "isMarried" : 1 }, { "Name" : "Mike", "isMarried" : 1 } ] }
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