Insert Trigger for Embedded Objects

I’m trying to add triggers to an object which has an embedded array of documents. How can I check if a new document has been created in the array. I’m making an app in SwiftUI and I’m fairly new to mongoDB. So from the documentation it seems like I can set up a trigger for an update operation and then check for the field updated. But the documents in the array can be edited so the update operation might not always be reliable to only look for documents created and can return an object that exists but has been edited. How can I work around this? Is there something in the documents I’m missing. Any help is appreciated, Thank you in advance.

Hi @Timothy_Tati and welcome to the MongoDB community forum!!

For better understanding of the requirement, it would be helpful if you confirm if my understanding is correct.

Are you looking for a trigger operation to insert in an array field for any new element inserted and not enabling the trigger on updating the existing element of the array?

Could you also confirm the below understanding for more clarity:

Is the trigger same as Atlas Triggers? If yes, could you also share the documentation link which you are referring for creating the Atlas trigger.

  1. Also, could you share the an example scenario with an example documents.
  2. Could you help me understand the importance of Swift UI for the above scenario.

Best regards


Thank you for getting back.

Sorry, There is no relevance of SwiftUI. Just wanted to establish that I was new to the web dev/backend side of things. Yes it’s an atlas trigger from the official docs

This is how the schema is set up. Every Post has a an Array of Comment Objects

 Post:  { comments: [Comments]  } // Linked Objects

And Every Comment has an array of embedded replies.

Comment:  { replies: [Reply]  } // Embedded Objects

The way the trigger is set up is that whenever the comment is updated. It runs a “newReply” function using the last element of the array. But I realised that if somebody edits their earlier reply that would count as an update operation as well, isn’t it? Needlessly running the “newReply” func on the same last element again. Currently I’m using the pre-image to compare the two but it feels too intensive for a simple task and I couldn’t find any docs where I could find such examples.

So yes is there a way to set up triggers which ONLY gets triggered if there’s
a new insert in the array( without using the doc pre-Image, if possible) and not when the array is updated.

Also if yes, will that work for all kinds of arrays irrespective of type?

Hi @Timothy_Tati and thank you for sharing the above information.

As schema design in MongoDB plays an important role and depending on the requirement, the solution may differ depending on the actual document you’re working with.
Therefore, it would be helpful if you could share a sample document for the above schema which would help me replicate and provide solution if it is possible.

Let us know if you have any further questions .

Best Regards

Hello Again. I think I might be complicating the question by providing the Post Schema. I’d like to ask a simple question, Is there a way to set up a trigger only for an array insertion? Whatever the value the array might hold, Documents, String, Int et al. So the trigger would go off whenever a new element is appended into the array and nothing else. Is that possible?

Hi @Timothy_Tati and welcome to the MongoDB community forum!!

The Triggers in MongoDB use the concept of change streams which works on the per document basis.
Therefore, for insert operation, it would be triggered when en entire new document is inserted into the collection.

Based on the above requirement, I tried to create a sample document with objects and array and tried to create triggers for insert and update operation individually.
Based on the documentation, the insert trigger is initiated when a new document is inserted whereas the update trigger is initiated when any sort of update is made to the document.
Modifying an array by adding new elements as per your requirement would fall under an update workflow.

Let us know if you have any further questions.

Best Regards