MongoDb query on two collections

Question

I have two collection as below First collection is Users:

{
"userid":123,
"name":"abc",
"age":20,
"status":"Active"
}
{
"userid":345
"name":"cde"
"age":25,
"status":"Active"
}

second collection is userComment:

{
"userid":123,
"commnet":"Mongodb rocks"
}

can anyone please help me writing the query to fetch the users with "Active" status alongwith a flag that will tell me whether user has any comment or not So the o/p should be

{
"userid":123,
"name":"abc",
"age":20,
"status":"Active"
"userscommentFlag":"Y"**
}
{
"userid":345
"name":"cde"
"age":25,
"status":"Active"
"userscommentFlag":"N"
}

Thanks.

If you are using mongo 3.2 latest version, you can use `$lookup` in the aggregation pipeline to join/populate fields from other collection. See https://docs.mongodb.com/manual/reference/operator/aggregation/lookup/ — Rudra, May 30 '16 at 04:52
Possible duplicate of [MongoDB query multiple collections at once](https://stackoverflow.com/questions/6502541/mongodb-query-multiple-collections-at-once) — Guilherme Ferreira, Sep 23 '19 at 18:25

score 1 · Answer 1 · answered May 30 '16 at 05:09

1

Using $lookup in aggregation pipeline this can be done as:

db.users.aggregate(
[{$lookup:
 {from:"userComment", localField:"userid", foreignField: "userid", as: "comments"
}}])

Note: $lookup is supported in mongodb 3.2

answered May 30 '16 at 05:09

Atish

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In mongodb , if you want to query from two collections , "$lookup" only used , its available in latest version – karthi May 30 '16 at 05:24
How I can add the "usercommentFlag" while using $lookup? – Ranjit May 30 '16 at 09:33

MongoDb query on two collections

1 Answers1