Does “Atomic Operations in MongoDB” have order of execution?

[MongoUser]

Which is order of execution of atomic operations in the following update method?

     db.foo.update({'_id': 'a'}, {'$push': {'things': 'thing1'}, '$inc': {'version': 1}

The First is '$push' and the second if '$inc' ?

Or the order of execution is unknown?

[Scott Hernandez]

The order is undefined. But both will happen to the document atomically; no read can happen in the middle of the write.

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[MongoUser]

Please look at the following code:

     db.foo.update({'_id': 'a'}, {'$pull' : {'things': 'thing1'} '$push': {'things': 'thing2'},)

I need to first pull 'thing1' and then push 'thing2' Is this possible in Mongodb?

четверг, 30 августа 2012 г., 14:50:56 UTC+4 пользователь Scott Hernandez написал:

[Scott Hernandez]

You will want to watch and vote for this feature for that
functionality: https://jira.mongodb.org/browse/SERVER-1050

[MongoUser]

But how it helps me if you have answered that the order of execution is undefined? What will be first $pull or $push?

четверг, 30 августа 2012 г., 15:33:19 UTC+4 пользователь Scott Hernandez написал:

[Scott Hernandez]

It is not supported and the issue I posted is the feature to enable that.

Have you tried to do it?

This is what you will get:
> db.a.save({_id:2, arr:[1,2,3]})
> db.a.update({_id:2}, {$push:{arr:1}, $pull:{arr:1}})
Field name duplication not allowed with modifiers

[MongoUser]

Thanks you Scott. I do understand that it's not supported yet. I've asked about if this will be realized in a future does it help me? Because as you  wrote:  The order is undefined. Because in my case I to $pull first and only then $push:

      db.foo.update({'_id': 'a'}, {'$pull' : {'things': 'thing1'} '$push': {'things': 'thing2'});

So I need a specific order when I use a 'Atomic Operations'. 

четверг, 30 августа 2012 г., 17:04:29 UTC+4 пользователь Scott Hernandez написал:

[Scott Hernandez]

Yeah, in order for it to work we would need to define an order and
that is a tricky problem depending on the operators and use-cases.
Specifying an explicit order could be complicated as well.

Feel free to add your thoughts to the issue/feature-request.