how to match array field and nested array field in mongodb without using unwind

Question

My json data will look like this

{
  "videoId": 29,
  "videoComments": [
    {
      "comment": "awsome",
      "userId": 15,
      "commentTime": "2022-03-01T12:37:49.734Z",
      "userName": "user1646127068323",
      "deletedbyowner": "FALSE",
      "_id": "621e139d8e4195079c86488",
      "replyComments": [
        {
          "replyComment": "thank you",
          "replyCommentTime": "2022-03-01T12:44:53.193Z",
          "replyDeletedbyowner": "FALSE",
          "_id": "621e154557fa7045e342540"
        }
      ]
    }
  ]
}

I need to match some conditions that I mentioned below :

match "videoId" == "29"
then match "videoComments.deletedbyowner" == "FALSE"
if I match second condition then I need to match "videoComments.replyComments.replyDeletedbyowner" == "FALSE"

I can't use unwind because my boss told me that unwind is a costly operation it will effect the app performance. so with out using unwind I need to match these conditions. could you please help out of this.

you want to keep the documents that match your creteria unchained? or you want to change the arrays also, to have only the members that much the creteria? — Takis
– Takis, Commented Mar 3, 2022 at 13:56
Is this what you are looking for? $elemMatch could be used when querying arrays. — ray
– ray, Commented Mar 3, 2022 at 14:02

Takis · Accepted Answer · 2022-03-03 15:25:48Z

1

Query

this keep the documents with videoId=29
only the elements with deletedbyowner="FALSE"
and only the elements with replyDeletedbyowner="FALSE"

*this is aggregate solution, we have also $elemMatch and $ to project the matched element, but here you need match on nested arrays, so i think you need aggregation, but i am not completly sure.

Test code here

aggregate(
[{"$match":{"$expr":{"$eq":["$videoId", 29]}}},
 {"$set":
  {"videoComments":
   {"$map":
    {"input":"$videoComments",
     "in":
     {"$cond":
      [{"$ne":["$$this.deletedbyowner", "FALSE"]}, null,
       {"$mergeObjects":
        ["$$this",
         {"replyComments":
          {"$filter":
           {"input":"$$this.replyComments",
            "cond":{"$eq":["$$reply.replyDeletedbyowner", "FALSE"]},
            "as":"reply"}}}]}]}}}}},
 {"$set":
  {"videoComments":
   {"$filter":
    {"input":"$videoComments", "cond":{"$ne":["$$this", null]}}}}}])

edited Mar 3, 2022 at 15:25

answered Mar 3, 2022 at 14:18

Takis

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2 Comments

Roopesh Krishna Over a year ago

this is perfectly working with my conditions thank you:)

Takis Over a year ago

@RoopeshKrishna ok good, if it works accept it as solution, this is for helping the one that answered, and for other people to know if answer worked and useful.

Shivam Mishra · Accepted Answer · 2022-03-03 14:06:21Z

0

collection_name.find(
  { videoId : 29 },
  { videoComments : { $elemMatch : { deletedbyowner : "FALSE", $elemMatch: { replyDeletedbyowner: "FALSE"} } }
).pretty();

I think this is what you are looking for. For more info check this doc

answered Mar 3, 2022 at 14:06

Shivam Mishra

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