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Message from discussion Support use Group to sum array of object.
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Stephen Steneker  
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 More options Sep 18 2012, 12:48 am
From: Stephen Steneker <stephen.stene...@10gen.com>
Date: Mon, 17 Sep 2012 21:48:14 -0700 (PDT)
Local: Tues, Sep 18 2012 12:48 am
Subject: Re: Support use Group to sum array of object.
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> My collections which have key is a array object.
> I need sum total as SQL statement:
>                    *Select Line_Items.Name , Sum(Line_Items.Quantity)
> from Orders group by Line_Items.Name*
> Could I use group to sum data instead of map/reduce?

Hi Tom,

You could use the Aggregation Framework in MongoDB 2.2 to sum the data by
name:

db.Orders.aggregate(
  { $unwind: "$Line_Items" },
  { $group : {
 _id: "$Line_Items.Name",
 Quantity: { $sum: "$Line_Items.Quantity"}
  }}
)

There are a few limitations to be aware of, in particular that the output
from the Aggregation Framework is limited to the maximum BSON document size
(16Mb): http://docs.mongodb.org/manual/applications/aggregation/#limitations.

You may also want to start your aggregation with an indexed $match to limit
the range of documents to aggregate.

> Have Mongodb support sum/avg key in array of Object by use Aggregation

Group/Map Reduce yet?

The new aggregation framework includes a number of mathematical functions
such as $sum, $avg, $min, and $max:
 http://docs.mongodb.org/manual/reference/aggregation/#arithmetic-oper...

Cheers,
Stephen


 
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