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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 }
]
}
Updated on: 02-Apr-2020
2K+ Views
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