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I have been looking at the docs and searching for videos on my problem, but I find nothing. I have a db called HPDASH where I have 2 collections, scripts and serverList. My problem is that I want to create a field for serverList that has the count() of the collection scripts.

I have tried this:
db.scripts.insert([{name: 'local_script'}, {name: 'qidsloader'}])
db.serverList.insert({script_count: db.scripts.count() })

The problem is that when I insert another record to scripts, the data on scripts_count stays as 2.

Is it possible to achieve this on MongoDB?

  • The short answer is no. Find the count whenever you need to use it. – joanolo Jul 29 '17 at 11:10
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As you have noticed, MongoDB doesn't support naturally triggers. So, you need "programming skills" to do that functionality. You can use mongoTriggers, what can installed with mongo-triggers npm package.

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A far more optimal solution exactly for this usecase would be use Redis to store the counts for the collection under a hashset while mongodb has the collection itself, this ensures your collection wont be locked for upserts, you can read more about this strategy HERE (Disclaimer: not my website)

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