PyMongo: Access fields returned from document within array resulting from find() query

Question

I am executing a query like this on a MongoDB collection:

 cursor = collection.find({"activityArray":{"$elemMatch":{"sport":0}}},{"activityArray.sport" : 1, "activityArray\|here is result object
.id":1, "endo" : 1})                                                                                                 |20166249
    for result_object in cursor[0:1]:                                                                                |here is result object
        print "here is result object"                                                                                |20166249                                                            |here is result object
        print result_object["endo"]                                                                                  |20166249
#        print result_object["activityArray.sport"]   
#        print result_object["activityArray"]["sport"]   
#        print result_object["sport"]

Each of the commented out lines gives me a key error. How can I access those fields returned from a document within an array within a document resulting from a PyMongo query?

chridam · Accepted Answer · 2015-06-02 19:15:54Z

1

Since activityArray is an array, you need to have another loop on that list as follows:

cursor = collection.find({"activityArray": {"$elemMatch": {"sport":0 }}},{"activityArray.sport" : 1, "activityArray.id":1, "endo" : 1}) 

for result_object in cursor[0:1]:
    print result_object["endo"])
    for activity in result_object["activityArray"]:
        print activity["sport"]

answered Jun 2, 2015 at 19:15

chridam

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2 Comments

sunny Over a year ago

Thanks. I had figured this out in parallel, but what I still don't understand is that I thought $elemMatch returns only the first array element matched? Apparently it actually returns the whole array so long as one element matches?

chridam Over a year ago

@sunny There are two different types of $elemMatch operators: 1) for querying and the other for projection. In your case you used the former instead of the latter.

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