Querying size of an array field

[Ram]

I have a collection called tags with the documents in the below
model.
Each document has a tagname field and mrid field. The mrid field is an
array.


{ "_id" : ObjectId("4f554c9ddc1def1a3a3ba62c"), "tagname" : "sql",
"mrid" : [ "60", "59" ] }
{ "_id" : ObjectId("4f554c9edc1def1a3a3ba62d"), "tagname" : "java",
"mrid" : [ "60" ] }


I need query the list of tagnames along with the size of the array.

the result should be like

select tagname, count(mrid).

result set: sql,2
java,1

How can I get this result?

[Nat]

You can use group command.

http://www.mongodb.org/display/DOCS/Aggregation#Aggregation-Group

[Scott Hernandez]

See group or mapreduce: http://www.mongodb.org/display/DOCS/Aggregation

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[Ram]

I am looking to get the size of the array. Is it possible with mapreduce. I think this is not possible with group.

On Monday, March 5, 2012 8:04:38 PM UTC-6, Scott Hernandez wrote:

See group or mapreduce: http://www.mongodb.org/display/DOCS/Aggregation

On Mon, Mar 5, 2012 at 8:52 PM, Ram <ramesh...@gmail.com> wrote:
> I have a collection called tags with the documents in the below
> model.
> Each document has a tagname field and mrid field. The mrid field is an
> array.
>
>
> { "_id" : ObjectId("4f554c9ddc1def1a3a3ba62c"), "tagname" : "sql",
> "mrid" : [ "60", "59" ] }
> { "_id" : ObjectId("4f554c9edc1def1a3a3ba62d"), "tagname" : "java",
> "mrid" : [ "60" ] }
>
>
> I need query the list of tagnames along with the size of the array.
>
> the result should be like
>
> select tagname, count(mrid).
>
> result set: sql,2
>               java,1
>
> How can I get this result?
>
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