php - MongoDB find count of all entries in child array by key -

i have collection in mongodb database looks this:

{   "_id": "0123456789",   "merchants": {     "13142": {       "deeplink1": "http://xx.tld",       "programid": 13142,       "price": 24.9,       "ean": "0123456789",       "shipping": 0.0,       "cf_farbe": "schwarz",       "cf_geschlecht": "men",       "cf_größe": "l",       "cf_imgurl2": "http://img.tld",       "cf_stamm-artikelnummer": "329830",       "cf_verfügbare größen": "s, l"     }   } } 

these merchant information products. _id product code, "merchants" array merchant id key.

now need count of entries of merchant specific merchant id ("13142" example). how can perform (with php mongoclient class)?

thanks help!

db.collenctionname.find({'merchants.13142':{$exists:true}}).count() give result in mongodb console, please convert according php .. in .net cann't told php code..

use '.' operator find inner level property.. here in answer used 'merchants.13142'