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MongoDB query to limit subdocuments having the given fields of the 'projection'
For this, use aggregate() in MongoDB. Let us create a collection with documents −
> db.demo285.insertOne(
... {... details : [
... {
... Name : "Chris"
... },
... {
... Name2: "Bob"
... },
... {
... Name: "Mike"
... }
... ]
... }
...)
{
"acknowledged" : true,
"insertedId" : ObjectId("5e4abffef49383b52759cbb9")
}Display all documents from a collection with the help of find() method −
> db.demo285.find();
This will produce the following output −
{ "_id" : ObjectId("5e4abffef49383b52759cbb9"), "details" : [ { "Name" : "Chris" }, { "Name2" : "Bob" }, { "Name" : "Mike" } ] }Following is the query to limit subdocuments having the given fields of the `projection` −
> db.demo285.aggregate(
... [
... { $match:
... {'details.Name' :
... { $exists: 1 }
... }
... },
... { $unwind: "$details" },
... { $match:
... {'details.Name' :
... { $exists: 1 }
... }
... },
... { $project: { Name: "$details.Name", _id: 0 } }
... ])This will produce the following output −
{ "Name" : "Chris" }
{ "Name" : "Mike" }
Updated on: 31-Mar-2020
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