Pymongo $push not updating array, no exception

Question

I have a document with a nested array that I can't seem to update, I have been going around in circles and it's starting to grate on me, here is the doc:

mongo =  pymongo.Connection()['FINS_ALL_L']['FIN_L']

f =         {'plant': 'local',
            'T1':{
            'PID':4278,
            'INST_SPECS' :{'unit_stk': 6386,
                           'thresh': 0.4,
                           'max_in': 789878,
                           'avg_cut': 45565},
            'PU_ARRAY'   : [{'power': 45789, 'unit': 78},{'power': 45757, 'unit': 1},{'power': 45127, 'unit': 11},{'power': 42567, 'unit': 10}]},

            'T2':{
            'PID':8422,
            'INST_SPECS' :{'unit_stk': 4575,
                           'thresh': 0.49,
                           'max_in': 187878,
                           'avg_cut': 14787},
            'PU_ARRAY'   : [{'power': 51475, 'unit': 7},{'power': 59895, 'unit': 2},{'power': 57578, 'unit': 3},{'power': 54525, 'unit': 15}]}}

    py_mong = mong.find_one({'plant':'local'})['T2']['PU_ARRAY']
    print py_mong

    >>>[{u'power': 51475, u'unit': 7}, {u'power': 59895, u'unit': 2}, {u'power': 57578, u'unit': 3}, {u'power': 54525, u'unit': 15}]

I have tried many variants of '$push', they don't throw an error, but they don't seem to update either. For example:

mongo.update({'plant': 'local','T2':'PU_ARRAY'},
                {'$push':
                     {'T2.$.PU_ARRAY':
                          {'power': 42577, 'unit': 19}
                      }
                 }
            )

This does not throw an exception, but yet, no update. Can someone help?

Blakes Seven · Accepted Answer · 2015-09-12 05:55:44Z

3

No match, no update. There is no such "value" under "T2", it's just a "field name". I don't know if you intended $exists but $push does not care. Also there is no need for the positinal $ operator in the statement as you would not even be matching an array position even if this were an $exists test. "T2" is not an array:

mongo.update(
   {'plant': 'local'},
   {'$push': { 'T2.PU_ARRAY': {'power': 42577, 'unit': 19 } } }
)

edited Sep 12, 2015 at 5:55

answered Sep 12, 2015 at 5:46

Blakes Seven

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2 Comments

ajsp Over a year ago

Thanks, I should really get my head into the docs, in a way this site is both a blessing and a curse (isn't complaining).

Blakes Seven Over a year ago

@ajsp As I said, I think you got yourself confused trying to test if "PU_ARRAY" exists under "T2". But "T2" is neither an "array" ( no need for positional match ) nor when you "dot notate" as shown an if the field was no already there yet then a new array field of that name with the entries you specify will be created. Otherwise the entries will be appended.

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