mongodb - mongoexport csv output last array values -

inspired question in server fault https://serverfault.com/questions/459042/mongoexport-csv-output-array-values

i'm using mongoexport export collections csv files, when try target fields last members of array cannot export correctly.

command i'm using

mongoexport -d db -c collection -fieldfile fields.txt --csv > out.csv 

one item of collection:

{     "id": 1,     "name": "example",     "date": [         {"date": ""},         {"date": ""},     ],     "status": [          "true",          "false",     ], } 

i can access first member of array writing fields following

name id date.0.date status.0 

is there way acess last item of array without knowing lenght of array?

because following doesn't work:

name id date.-1.date status.-1 

any idea of correct notation? or if it's not possible?

it's not possible reference last element of array without knowing length of array, since notation array_field.index index in [0, length - 1]. use aggregation framework create view of data want export, save temporarily collection $out, , mongoexport that. example, documents do

db.collection.aggregate([     { "$unwind" : "$date" },     { "$group" : { "_id" : "$_id", "date" : { "$last" : "$date" } } },     { "$out" : "temp-for-csv" } ]) 

in order last date each document , output collection temp-for-csv.

you can return last elements in array $slice projection operator, isn't available in aggregation , mongoexport takes query specification, not projection specification, since --fields , --fieldfile option supposed suffice. might feature request ask using query projection mongoexport.