$push and $set in same update query with condition $cond pymongo mongodb

Question

I'm trying to update my collection

For the single, object need to update the status and updated time.

Input object id as id new status as current status

Condition If the new status is different from the status in DB, then need to $push new status and timestamp into activity_log array. And update the update the updated_time and status of the record.

If the new status and previous status is same then updated_time will be updated.

Is it possible to do that in pymongo using single update ?

collection.update({
        '_id': ObjectId(id),
    }, {
        '$cond': {
            'if': {
                'status': {
                    '$ne': current_status
                }
            },
            'then': {
                '$push': {
                    'activity_log': {
                        'status': current_status,
                        'changed_time': datetime.now()
                    }
                }
            },
            'else': None
        },
        '$set': {
            'status': current_status,
            'updated_time': datetime.now()
        }
    })

Please edit this question with 1) Sample doc , 2) Input , 3) Conditions to be applied & 4) result doc after update applied !! Db version ? — whoami - fakeFaceTrueSoul, May 08 '20 at 06:17
Updated with the input and condition mongodb version is `MongoDB 4.2.5 Community`. — wulfnb, May 08 '20 at 07:20
I have updated my answer, It is possible to do it in a single query, I have tried it on Mongo client the updated query is working, please check. — Puneet Singh, May 08 '20 at 15:01

Puneet Singh · Answer 1 · 2020-05-08T15:00:31.310

You can do that in a single query, From MongoDB 4.2 update query supports aggregation pipeline, You can do that as per below code

collection.update(
     {'_id': ObjectId(id)}, 
     [{'$set': {
            'status': current_status,
            'updated_time': datetime.now(),
            'activity_log':{
              '$cond': {
                'if': {'$ne': ['$status',current_status]},
                'then': {$concatArrays:['$activity_log',[
                          {
                           'status': current_status,
                           'changed_time': datetime.now()
                          }
                ]]},
                'else': '$activity_log'
            }
      }}}]
)

score 1 · Answer 2 · answered May 08 '20 at 09:09

The $cond operator is not flow control like if-then-else, it is an expression that returns a value.

If you want to conditionally update a field based on the value of another field in the same document, you can use the pipeline form of update, assigning the field the result of the $cond expression.

collection.update(
     {'_id': ObjectId(id)}, 
     [{'$set': {
            'status': current_status,
            'updated_time': datetime.now(),
            'activity_log':{
              '$cond': {
                'if': {'$ne': ['$status',current_status]}
                'then': {$concatArrays:['$activity_log',[
                          {
                           'status': current_status,
                           'changed_time': datetime.now()
                          }
                ]]},
                'else': '$activity_log'
            }
      }}]
)

I think the above way is correct pymongo is triggering ```in validate_is_mapping raise TypeError("%s must be an instance of dict, bson.son.SON, or " TypeError: document must be an instance of dict, bson.son.SON, or any other type that inherits from collections.Mapping``` — wulfnb, May 08 '20 at 15:27
The pipeline form of update as added in MongoDB 4.2. If the version of pymongo you are using doesn't support that in the `update` function, you might be able to run the [update](https://docs.mongodb.com/manual/reference/command/update/index.html#update) database command using [db.command](https://stackoverflow.com/a/27298423/2282634) — Joe, May 08 '20 at 16:37

$push and $set in same update query with condition $cond pymongo mongodb

2 Answers2