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Push to last element of sub-array

Can you have mongo $push prepend instead of append?How to Update Multiple Array Elements in mongodbmongodb push element into array of objectsGetting first and last element of array in MongoDBMongodb update deeply nested subdocumentMongo Aggregation select and push last element in arrayHow to filter sub array and project multiple matching values of a matching document in mongoDbmongodb: How to create _id for each array element?Pushing into sub document array inside by elementmongodb: push to subarray of array element or add to array if not existingMongoDB push record in array

.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty height:90px;width:728px;box-sizing:border-box;

0

My document looks like this:

 _id: ...
 checkins: [
 ...
 ...
 
 ...
 activities: [
 ...
 ...
 ]
 
 ]

If I want to push into the first element of the checkins array I could do this:

mycol.updateOne(
 '_id': ...,
 '$push': 
 'checkins.0.activities': entry
 )

But I need to insert entry into the last index of the checkins array, so how could I implement something like this?

mycol.updateOne(
 '_id': ...,
 '$push': 
 'checkins.-1.activities': entry
 )

Edit:

I can't just do:

'$set': 'checkins.-1': <entry>

Because it'd overwrite the other elements in the array, and this:

'$set': 'checkins.-1': [...otherEntries, entry]

Would mean inserting the whole array every single time, and since it's very big array, it'd be way too expensive

This, as suggested, looks promising, though:

 $each: [ entry ],
 $position: -1

But this just lets me push into the checkins array, if I wanted to add an element to the activities subarray it'd involve inserting the whole array, just like the first solution. In this case, I'm looking for something like this:

 $each: '$push': 'activities': entry ,
 $position: -1

But of course it does not work, mongo complains that

The argument to $each in $push must be an array but it was of type: object

How do I push into the last element, i.e. into checkins.-1.activities?

mongodb

share|improve this question

edited Mar 25 at 17:20

arielnmz

asked Mar 23 at 18:41

arielnmzarielnmz

3,63031939

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Possible duplicate of Can you have mongo $push prepend instead of append?
  
  – manish kumar
  Mar 23 at 18:44
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Not quite, the syntax doesn't work the same when dealing with nested arrays. Also, I'd rather not $set the entire activities array every time I need to push one activity
  
  – arielnmz
  Mar 23 at 18:50
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Nested arrays are really bad. Basically impossible to atomically update before relatively recent changes for MongoDB, and mostly they just don't deliver as a structure what you "think" you designed them for. Typically people think "like a relation", but it's not actually how you do it. The -1 problem has long be dealt with by basically "reversing the order of the array", which is the real use case of $position and $sort modifiers. You would be better of actually showing you full use case, since the solution would certainly be to "flatten" the arrays and reverse the order.
  
  – Neil Lunn
  Mar 23 at 23:54
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  In other words "show what actually needs to get done" rather than discuss how you think it needs to be done. And be prepared to make structural changes to data.
  
  – Neil Lunn
  Mar 23 at 23:56
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  show what actually needs to get done Its literally in the two examples. I had to add why they don't work because the site prompted me to add why the suspected dupe isn't a dupe. Typically people think "like a relation" that's totally not what I think, please if you need more info ask for it but don't start a discussion. The -1 problem has long be dealt with by basically "reversing the order of the array" So, how does one reverse the order of an embedded array within another array? Or use $position and $sort within arrays?
  
  – arielnmz
  Mar 25 at 17:02
  
  

  
  
  
  

 | 
show 1 more comment

0

My document looks like this:

 _id: ...
 checkins: [
 ...
 ...
 
 ...
 activities: [
 ...
 ...
 ]
 
 ]

If I want to push into the first element of the checkins array I could do this:

mycol.updateOne(
 '_id': ...,
 '$push': 
 'checkins.0.activities': entry
 )

But I need to insert entry into the last index of the checkins array, so how could I implement something like this?

mycol.updateOne(
 '_id': ...,
 '$push': 
 'checkins.-1.activities': entry
 )

Edit:

I can't just do:

'$set': 'checkins.-1': <entry>

Because it'd overwrite the other elements in the array, and this:

'$set': 'checkins.-1': [...otherEntries, entry]

Would mean inserting the whole array every single time, and since it's very big array, it'd be way too expensive

This, as suggested, looks promising, though:

 $each: [ entry ],
 $position: -1

But this just lets me push into the checkins array, if I wanted to add an element to the activities subarray it'd involve inserting the whole array, just like the first solution. In this case, I'm looking for something like this:

 $each: '$push': 'activities': entry ,
 $position: -1

But of course it does not work, mongo complains that

The argument to $each in $push must be an array but it was of type: object

How do I push into the last element, i.e. into checkins.-1.activities?

mongodb

share|improve this question

edited Mar 25 at 17:20

arielnmz

asked Mar 23 at 18:41

arielnmzarielnmz

3,63031939

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Possible duplicate of Can you have mongo $push prepend instead of append?
  
  – manish kumar
  Mar 23 at 18:44
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Not quite, the syntax doesn't work the same when dealing with nested arrays. Also, I'd rather not $set the entire activities array every time I need to push one activity
  
  – arielnmz
  Mar 23 at 18:50
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Nested arrays are really bad. Basically impossible to atomically update before relatively recent changes for MongoDB, and mostly they just don't deliver as a structure what you "think" you designed them for. Typically people think "like a relation", but it's not actually how you do it. The -1 problem has long be dealt with by basically "reversing the order of the array", which is the real use case of $position and $sort modifiers. You would be better of actually showing you full use case, since the solution would certainly be to "flatten" the arrays and reverse the order.
  
  – Neil Lunn
  Mar 23 at 23:54
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  In other words "show what actually needs to get done" rather than discuss how you think it needs to be done. And be prepared to make structural changes to data.
  
  – Neil Lunn
  Mar 23 at 23:56
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  show what actually needs to get done Its literally in the two examples. I had to add why they don't work because the site prompted me to add why the suspected dupe isn't a dupe. Typically people think "like a relation" that's totally not what I think, please if you need more info ask for it but don't start a discussion. The -1 problem has long be dealt with by basically "reversing the order of the array" So, how does one reverse the order of an embedded array within another array? Or use $position and $sort within arrays?
  
  – arielnmz
  Mar 25 at 17:02
  
  

  
  
  
  

 | 
show 1 more comment

My document looks like this:

 _id: ...
 checkins: [
 ...
 ...
 
 ...
 activities: [
 ...
 ...
 ]
 
 ]

If I want to push into the first element of the checkins array I could do this:

mycol.updateOne(
 '_id': ...,
 '$push': 
 'checkins.0.activities': entry
 )

But I need to insert entry into the last index of the checkins array, so how could I implement something like this?

mycol.updateOne(
 '_id': ...,
 '$push': 
 'checkins.-1.activities': entry
 )

Edit:

I can't just do:

'$set': 'checkins.-1': <entry>

Because it'd overwrite the other elements in the array, and this:

'$set': 'checkins.-1': [...otherEntries, entry]

Would mean inserting the whole array every single time, and since it's very big array, it'd be way too expensive

This, as suggested, looks promising, though:

 $each: [ entry ],
 $position: -1

But this just lets me push into the checkins array, if I wanted to add an element to the activities subarray it'd involve inserting the whole array, just like the first solution. In this case, I'm looking for something like this:

 $each: '$push': 'activities': entry ,
 $position: -1

But of course it does not work, mongo complains that

The argument to $each in $push must be an array but it was of type: object

How do I push into the last element, i.e. into checkins.-1.activities?

mongodb

share|improve this question

edited Mar 25 at 17:20

arielnmz

asked Mar 23 at 18:41

arielnmzarielnmz

3,63031939

 _id: ...
 checkins: [
 ...
 ...
 
 ...
 activities: [
 ...
 ...
 ]
 
 ]

mycol.updateOne(
 '_id': ...,
 '$push': 
 'checkins.0.activities': entry
 )

mycol.updateOne(
 '_id': ...,
 '$push': 
 'checkins.-1.activities': entry
 )

'$set': 'checkins.-1': <entry>

'$set': 'checkins.-1': [...otherEntries, entry]

 $each: [ entry ],
 $position: -1

 $each: '$push': 'activities': entry ,
 $position: -1

share|improve this question

edited Mar 25 at 17:20

arielnmz

asked Mar 23 at 18:41

arielnmzarielnmz

3,63031939

share|improve this question

edited Mar 25 at 17:20

arielnmz

asked Mar 23 at 18:41

arielnmzarielnmz

3,63031939

asked Mar 23 at 18:41

arielnmzarielnmz

3,63031939

asked Mar 23 at 18:41

arielnmzarielnmz

3,63031939