I am trying to query a mongo database from R using RMongo and return the values of a couple nested documents.
Looking through the documentation for RMongo, I understand the following query:
output <- dbGetQueryForKeys(mongo, 'test_data', '{"foo": "bar"}', '{"foo":1}')
Where the arguments are...
db = mongo
collection = 'test_data'
query = '{"foo": "bar"}'
keys = 'Specify a set of keys to return.'
What is the 1 in '{"foo":1}'? What is the structure of this key set? Checking against this blog post, I found a format like:
result < - dbGetQueryForKeys(mongo, "items", "{'publish_date' : { '$gte' : '2011-04-01', '$lt' : '2011-05-01'}}", "{'publish_date' : 1, 'rank' : 1}")
So, apparently, the keys need the value 1?
How would I get keys for nested documents? If I wanted something like...
output <- dbGetQueryForKeys(mongo, 'test_data', '{"foo": "bar"}', '{"foo1.foo2.foo3.foo4":1,"foo1.foo2.foo3.bar4":1}')
For nested keys, I'm currently returning something more like...
X_id
1 50fabd42a29d6013864fb9d7
foo1
1 { "foo2" : { "foo3" : { "foo4" : "090909" , "bar4" : "1"}}}
...where output[,2] is a looooong string, rather than as two separate variables for the values associated with the keys foo4 and bar4, ("090909", "1") as I would have expected.
What is the 1 in '{"foo":1}'? What is the structure of this key set?
These keys are the query projections to return for read operations in MongoDB. A value of "1" means to include a specific field and "0" excludes. The default behaviour is to include all fields in the projection.
How would I get keys for nested documents?
For nested keys, I'm currently returning something more like... 1 { "foo2" : { "foo3" : { "foo4" : "090909" , "bar4" : "1"}}} ...where output[,2] is a looooong string, rather than as two separate variables for the values associated with the keys foo4 and bar4, ("090909", "1") as I would have expected.
The RMongo driver is returning data including the embedding hiearchy.
You can reshape & flatten the result output using the RMongo dbAggregate() command and the $project operator which is part of the Aggregation Framework in MongoDB 2.2+.