Re: [mongodb-user] selecting part of array within document: is thsi still the restriction in 2.2 or 2.3?

[Sam Millman]

This should be possible with the positonal operator return in 2.2: https://jira.mongodb.org/browse/SERVER-1243

On 1 September 2012 01:37, MONGOALAL <anuj...@gmail.com> wrote:

This was raised earlier in 2010 and wondering whether this restriction is still there? I'd like to avoid doing this by mapreduce.

Appreciate quick reply from gurus

http://stackoverflow.com/questions/3985214/mongodb-extract-only-the-selected-item-in-array

Suppose you have the following:

// Document 1
{ "shapes" : [
  {"shape" : "square", "color" : "blue"},
  {"shape" : "circle","color" : "red"}
  ] 
}


// Document 2
{ "shapes" : [
  {"shape" : "square",  "color" : "black"},
  {"shape" : "circle",  "color" : "green"}
  ] 
}

do query:

 db.test.find({"shapes.color":"red"}, {"shapes.color":1})

or

db.test.find({shapes: {"$elemMatch": {color: "red"}}}, {"shapes.color":1})

return document (Document 1) matched, but with always ALL array items in shapes:

{ "shapes" : [
  {"shape" : "square", "color" : "blue"},
  {"shape" : "circle","color" : "red"}
  ] 
}

I just want document (Document 1) filtered with ONLY array item color=red:

{ "shapes" : [
  {"shape" : "circle","color" : "red"}
  ] 
}

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[MONGOALAL]

yes i tried that but it gives only first row and not all matching rows from array

see this

https://groups.google.com/forum/?fromgroups=&hl=en#!topic/mongodb-user/Qwn7vnILo74

anuj

[MONGOALAL]

can someone clarify returning first matching row only is intended functionality or bug?

Based on doc, it appears to be bug.

Appreciate if some one can clarify

On Saturday, September 1, 2012 3:34:40 AM UTC-7, Sammaye wrote:

[Stephen Steneker]

can someone clarify returning first matching row only is intended functionality or bug?

Based on doc, it appears to be bug.

Appreciate if some one can clarify

Hi,

The positional operator currently only returns the first match found per document.

If you want to manipulate arrays as separate documents, you need to reshape your output using Map/Reduce or the new Aggregation Framework (MongoDB 2.2).

With the Aggregation Framework you can use $unwind to separate an array into a stream of documents, and then use other operators like $match or $group as appropriate to filter and recombine.

I've added an example to the Stack Overflow post you referenced:

 http://stackoverflow.com/questions/3985214/mongodb-extract-only-the-selected-item-in-array/12241733

Cheers,

Stephen