How to find duplicate values in different object fields?

Question

How can I search with mongoose to find duplicate values in different fields?

Here is sample document:

{
 "followers": {
               {
                "_id": "5bf6d610d3a3f31a6c75a9f4"
               },
               {
                "_id": "5bf6d610d3a3f31a6c75a8c3"
               }
              },
 "following": {
               {
                "_id": "5bf6d610d3a3f31a6c75a9f4"
               },
               {
                "_id": "5bf6d610d3a3f31a6c75b7a2"
               }
              },
}

I want to find same _id values under followers and following fields.

Expected Output:

{
 {
  "_id": "5bf6d610d3a3f31a6c75a9f4"
 }
}

What query should I use?

followers and following would be the Array. right?

Hardik Shah
– Hardik Shah

2018-11-29 11:31:42 +00:00
Commented Nov 29, 2018 at 11:31 — Hardik Shah
– Hardik Shah, Commented Nov 29, 2018 at 11:31
@HardikShah yes!

Omid
– Omid

2018-11-29 11:32:10 +00:00
Commented Nov 29, 2018 at 11:32 — Omid
– Omid, Commented Nov 29, 2018 at 11:32

Hardik Shah · Accepted Answer · 2018-11-29 12:01:25Z

2

Try with this:

db.collection.aggregate([
    { $unwind : "$followers"},
    { $unwind : "$following"},
    { $project : {
        _id: 0,
        matchId: { $cond: [ {$eq: [ "$followers._id", "$following._id" ]} ,
          "$following._id", null ] }
    }},
    {$match : {"matchId" : {$ne : null}}}
])

Output:

/* 1 */
{
    "matchId" : "5bf6d610d3a3f31a6c75a9f4"
}

answered Nov 29, 2018 at 12:01

Hardik Shah

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2 Comments

Omid Over a year ago

Thank you but How I can query within a single document( I want to find duplicate ids in a single document but in two different fields)

Hardik Shah Over a year ago

Yes, you can with the same snippet I have provided. Just to add $match to specific Id at the top level of aggregation. Can you post your whole sample data struct? So, I can modify with your requirement.

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