CODEWITHSUNDEEP
mongodbpymongo
Vladimir Vargas
Vladimir Vargas

Reputation: 1824

Pymongo query on "subdocuments"

Each instance of a collection called groups has a field called actives, which is a list of "subdocuments", i.e. things of the form {keys: values}. One field (key) of the subdocuments is id_, which is a string.

If I take the set of all subdocuments present in all the instances of groups, then there won't be 2 equal id_, i.e. id_ identifies uniquely each subdocument. However, I get a new subdocument. I need to run a program with the subdocument's id that will go to a website and extract info about the subdocument. Within this info I find the group that the subdocument belongs to. However, I don't want to run this program if I already have some subdocument, in some instance of groups with the same id_ as the "new" subdocument.

How can I list the ids of all the subdocuments of all the documents (or instances of groups)?

Edit:

Suppose that the documents of the DB groups are:

doc1: {"neighbourhood": "n1", "actives": [{"id_": "MHTEQ", "info": "a_long_string"}, {"id_": "PNPQA", "info": "a_long_string"}]}

doc2: {"neighbourhood": "n2", "actives": [{"id_": "MERVX", "info": "a_long_string"}, {"id_": "ZDKJW", "info": "a_long_string"}]}

What I want to do is to list all the "id_", i.e.

def list_ids(groups):
    do_sth_with_groups
    return a_list

print(list_ids(groups))

output: ["MHTEQ", "PNPQA", "MERVX", "ZDKJW"]

Upvotes: 0

Views: 1500

Answers (1)

Spydakat
Spydakat

Reputation: 36

Use the aggregation pipeline with the $unwind and $project operators.

results = db['collection'].aggregate(
  [
    {"$project": {"actives": 1, "_id": 0}},
    {"$unwind": "$actives"},
    {"$project": {"id_str": "$actives.id_", "_id": 0}}
  ]
)
return list(results)

https://docs.mongodb.com/v3.2/reference/operator/aggregation/unwind/ https://docs.mongodb.com/v3.2/reference/operator/aggregation/project/

Sample output

{ 
    "id_str" : "MHTEQ"
}
{ 
    "id_str" : "PNPQA"
}
{ 
    "id_str" : "MERVX"
}
{ 
    "id_str" : "ZDKJW"
}

Upvotes: 1

Related Questions