Update field inside array with '$inc'

[diegomsana]

I'm trying to update a field that's inside an array in a document
using the modifier '$inc', but it's not working.

E.g, i want to increment "b". This:
>db.collection.update( { _id:2 }, { $inc: { c : { b : 1} } }); does not work and does not throw any error message.

Is it possible to have this working in a next version?

[Eliot Horowitz]

Can you print out what the object look likes before and after that operation?

[diegomsana]

It's the same before and after the operation:

{"_id" : 2 , "c" : [{"b" : 1}]}

Changing the document to this {"_id" : 2 , "c" : {"b" : 1}} doesn't
work either.

On 16 jul, 21:42, Eliot Horowitz <eliothorow...@gmail.com> wrote:
> Can you print out what the object look likes before and after that operation?
>

[Eliot Horowitz]

I'm not sure this makes sense.
Do you think it should increment the b of every object in the array?
That seems a little weird to me.

[Wouter]

Use dotnotated strings to reach into objects/arrays.

{"_id" : 2 , "c" : {"b" : 1}}

db.collection.update({_id:2},{ $inc : { 'c.b': 1 }});

or

{"_id" : 2 , "c" : [{"b" : 1}]}

db.collection.update({_id:2},{ $inc : { 'c.0.b': 1 }});

(note the extra 0 (zero) to identify the key of the object in the
array)

[diegomsana]

Thanks Wouter, "db.collection.update({_id:2},{ $inc : { 'c.b': 1 }})"
worked.

Eliot: actually a real document would be something more like {"_id" :
3 , "c" : {"b" : 1, "c" : 1 , "d" : 2} , "a" : {"a" : 1, "b":1}}, by
doing such update i expect to change only field c.b: {"_id" : 3 ,
"c" : {"b" : 2, "c" : 1 , "d" : 2} , "a" : {"a" : 1, "b":1}}.

By the way, in php it's possible to use the dot notation. My code to
do this is like:
$doc = array("c.b" => 1);
$collection->update(array("_id"=>3), array('$inc' => $doc), true)

Don't remember seeing this possibility mentioned in the php docs.

Thanks.

[Kristina Chodorow]

By the way, if you think a certain example would help other users and you have the time, please add it to the manual.  The PHP documentation lets uses add comments at the bottom of every page.

[diegomsana]

sure, i'll do that soon.

On Jul 17, 5:03 pm, Kristina Chodorow <krist...@10gen.com> wrote:
> By the way, if you think a certain example would help other users and you
> have the time, please add it to the manual.  The PHP documentation lets uses
> add comments at the bottom of every page.
>

[Hien Nguyen]

Hello,

Thanks Wouter for your answer. However if I have a boucle "for" and I have to replace 0 (the key of the object) by an index i. It will not word anymore with 'c.i.b'.

How can I solve the problem? 

[Kevin Adistambha]

Hi Hien,

Hello,
Thanks Wouter for your answer. However if I have a boucle “for” and I have to replace 0 (the key of the object) by an index i. It will not word anymore with ‘c.i.b’.
How can I solve the problem?

Please note that you are replying to a thread that is seven years old. The problems this thread is discussing is likely not relevant to your issue.

Could you open a new thread with more details about:

• What are you trying to achieve
• What MongoDB version are you using
• What have you tried so far
• What error message(s) are you seeing

Best regards,
Kevin

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