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Perform $lookup to array of object id's in MongoDB?
For this, use $lookup. This performs a left outer join to an unsharded collection in the same database to filter in documents from the “joined” collection for processing.
Let us first create a collection with documents −
> db.demo395.insertOne({Name:"Chris"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e5e782317aa3ef9ab8ab207")
}
> db.demo395.insertOne({Name:"David"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e5e782317aa3ef9ab8ab208")
}Display all documents from a collection with the help of find() method −
> db.demo395.find();
This will produce the following output −
{ "_id" : ObjectId("5e5e782317aa3ef9ab8ab207"), "Name" : "Chris" }
{ "_id" : ObjectId("5e5e782317aa3ef9ab8ab208"), "Name" : "David" }Let us create a second collection with documents −
> db.demo396.insertOne({"details" : [
... ObjectId("5e5e782317aa3ef9ab8ab207"),
... ObjectId("5e5e782317aa3ef9ab8ab208")
... ]
... }
... )
{
"acknowledged" : true,
"insertedId" : ObjectId("5e5e787817aa3ef9ab8ab209")
}Display all documents from a collection with the help of find() method −
> db.demo396.find();
This will produce the following output −
{ "_id" : ObjectId("5e5e787817aa3ef9ab8ab209"), "details" : [
ObjectId("5e5e782317aa3ef9ab8ab207"), ObjectId("5e5e782317aa3ef9ab8ab208") ] }Following is the query to perform $lookup to array of object id's −
> db.demo396.aggregate([
... { "$lookup": {
... "from": "demo395",
... "let": { "details": "$details" },
... "pipeline": [
... { "$match": { "$expr": { "$in": [ "$_id", "$$details" ] } } }
... ],
... "as": "output"
... }}
... ])This will produce the following output −
{ "_id" : ObjectId("5e5e787817aa3ef9ab8ab209"), "details" : [ ObjectId("5e5e782317aa3ef9ab8ab207"), ObjectId("5e5e782317aa3ef9ab8ab208") ], "output" : [ { "_id" : ObjectId("5e5e782317aa3ef9ab8ab207"), "Name" : "Chris" }, { "_id" : ObjectId("5e5e782317aa3ef9ab8ab208"), "Name" : "David" } ] }
Updated on: 02-Apr-2020
2K+ Views
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