How to add or remove a element in double nested array?

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Example of the document:

{
    postId:'232323',
    post:'This is my first post',
    commentsOnPost:[
        {
            commentId:'232323_8888',
            comment:'Congrats',
            repliesOnPost:[
                {
                    replyId:'232323_8888_66666',
                    reply:'Thanks',
                    likesOnReply:['user1','user5','user3'],
                    
                }
            ]
        }
    ]
}

I want to add userid in likesOnReply if users do not exist in likesOnReply, similarly remove userid from likesOnReply if exist.

I have tried like this but not working properly

   await collection('post').findOneAndUpdate(
                {
                    postId: postId,
                    'commentsOnPost.commentId': commentId,
                    'commentsOnPost.repliesOnPost.replyId': replyId
                },
                {

                    $push: { 'commentsOnPost.$[].repliesOnPost.$.likes': userid },
                },

            );
mongodb-nodejs-driver mongodb-query express node.js mongodb
1 Answers

There is no straight way to do both the operation to pull or push in a single query,

There are 2 approaches,

1) Find and update using 2 queries:

  • use arrayFilters to updated nested array elements
  • $push to insert element
  • $pull to remove element
var post = await collection('post').findOne({
  posted: postId,
  ommentsOnPost: {
    $elemMatch: {
      commentId: commentId,
      repliesOnPost: {
        $elemMatch: {
          replyId: replyId
          likesOnReply: userid
        }
      }
    }
  }
});

var updateOperator = "$push";
// FOUND USER ID THEN DO REMOVE OPERATION
if (post) updateOperator = "$pull";

// QUERY
await collection('post').updateOne(
  { postId: postId },
  {
    [updateOperator]: {
      "commentsOnPost.$[c].repliesOnPost.$[r].likesOnReply": userid
    }
  },
  {
    arrayFilters: [
      { "c.commentId": commentId },
      { "r.replyId": replyId }
    ]
  }
)

Playground

2) Update with aggregation pipeline starting from MongoDB 4.2:

  • $map to iterate loop of commentsOnPost array check condition if commentId match then go to next process otherwise return existing object
  • $mergeObjects to merge current object with updated fields
  • $map to iterate loop of repliesOnPost array and check condition if replyId match then go to next process otherwise return an existing object
  • check condition for likesOnReply has userid then do remove using $filter otherwise insert using $concatArrays
await collection('post').findOneAndUpdate(
  { postId: "232323" },
  [{
    $set: {
      commentsOnPost: {
        $map: {
          input: "$commentsOnPost",
          in: {
            $cond: [
              { $eq: ["$$this.commentId", commentId] },
              {
                $mergeObjects: [
                  "$$this",
                  {
                    repliesOnPost: {
                      $map: {
                        input: "$$this.repliesOnPost",
                        in: {
                          $cond: [
                            { $eq: ["$$this.replyId", replyId] },
                            {
                              $mergeObjects: [
                                "$$this",
                                {
                                  likesOnReply: {
                                    $cond: [
                                      { $in: [userid, "$$this.likesOnReply"] },
                                      {
                                        $filter: {
                                          input: "$$this.likesOnReply",
                                          cond: { $ne: ["$$this", userid] }
                                        }
                                      },
                                      {
                                        $concatArrays: ["$$this.likesOnReply", [userid]]
                                      }
                                    ]
                                  }
                                }
                              ]
                            },
                            "$$this"
                          ]
                        }
                      }
                    }
                  }
                ]
              },
              "$$this"
            ]
          }
        }
      }
    }
  }]
)

Playgorund

user_89871280
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