Is there a way to insert a document in collection using aggregation pipeline?

Working with Data
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Hi there, are there any ways to insert a document using aggregation pipeline?

2

I am not sure of your use-case but you could take a look at

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Hi @steevej , I am pretty much looking for a aggregation pipeline substitution of db.collection().insert() function

4

That is what $merge is about. It insert documents, created by the execution of an aggregation, into a target collection.

An alternative is $out.

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I am pretty much looking for a aggregation pipeline substitution of db.collection().insert()

Why can’t you just use insert? Can you elaborate on the functionality you need? Rather than $merge I suspect you probably want to use update with upsert flag set to true and aggregation pipeline syntax to specify the update (available since version 4.2).

Asya

6

Yes, there is. It’s not a legitimate way, but it’s a workaround.
I wanted to do a complex upsert, which was not supported by a simple update. I stumbled upon this thread, but I didn’t give up. After some tweaking I was able to do it.

Even if you have 0 documents, you can make one using any stage to obtain at least one property. From then on, it’s game on.
This is just an example to upsert 1 document at time, the trick can be achieved using $facet. Below an example:
[ { '$facet': { dummy: [ { '$project': { validPropertyOfCollection: '' } } ] } }, { '$set': { yourProperties: 'test' } }, { '$unset': 'dummy' }, ... complexPipeline { '$merge': { into: 'yourCollection', on: 'yourUniqueField', whenMatched: 'replace', whenNotMatched: 'insert' } } ]

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The $documents stage might also be used when you do not have any collection to start with.

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