CODEWITHSUNDEEP
mongodbserializationtransactionsisolation
Joe Volcano
Joe Volcano

Reputation: 783

MongoDB Chain queries, pseudo transactions

I understand you cannot do transactions in MongoDB and the thinking is that its not needed because everything locks the whole database or collection, I am not sure which. However how then do you perform the following?

How do I chain together multiple insert, update, delete or select queries in mongodb so that other queries that might operate on the same data wait until these queries finish? An analogy would be serialization transaction isolation in ms sql server.

more..

I want to insert/update record into collection A and update a record in collection B and then read Collection A and B but I don't want anyone (process or thread) to read or write to collection A or B until BOTH A and B have been updated or inserted by the first queries.

Upvotes: 3

Views: 5231

Answers (1)

Markus W Mahlberg
Markus W Mahlberg

Reputation: 20703

Yes, that's absolutely possible.

It is called ordered bulk operations on planet Mongo and works like this in the mongo shell:

bulk = db.emptyCollection.initializeOrderedBulkOp()
bulk.insert({name:"First document"})
bulk.find({name:"First document"})
       .update({$set:{name:"First document, updated"}})
bulk.execute()
bulk.findOne()
> {_id: <someObjectId>, name:"First document, updated"}

Please read the manual regarding Bulk Write Operations for details.

Edit: Somehow is misread your question. It isn't possible for two collections. Remember though, that you can have different documents in one collection. Some ODMs even allow to have different models saved to the same collection. Exploiting this, you should be able to achieve what you want using the above bulk operations. You may want to combine this with locking to prevent writing. But preventing reading and writing would be the same as an transaction in terms of global and possibly distributed locks.

Upvotes: 2

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