How can I use a $elemMatch on first level array?

Question

Consider the following document:

{
  "_id" : "ID_01",
  "code" : ["001", "002", "003"],
  "Others" : "544554"
}

I went through this MongoDB doc for elemmatch-query & elemmatch-projection, but not able to figure it out how to use the same for the above document.

Could anyone tell me how can I use $elemMatch for the field code?

An example of your current query and the result you are trying to achieve would be very helpful. It sounds like you do want an $in query. — Stennie
– Stennie, Commented Apr 22, 2013 at 13:04

WiredPrairie · Accepted Answer · 2015-01-14 14:04:50Z

14

You'll want to use the $in operator rather than $elemMatch in this case as $in can be used to search for a value (or values) inside a specific field. $in requires a list of values to be passed as an array. Additionally, and for your case, it will find either a single value, or by searching in an array of values. The entire matching document is returned.

For example, you might use it like this:

db.mycodes.find( { code: { $in: ["001"] } } )

Which could be simplified to just be:

db.mycodes.find({ code: "001" })

As MongoDB will look in an array for a single match like above ("001").

Or if you want to search for "001" or "002":

db.mycodes.find( { code: { $in: ["001", "002"] } } )

$in documentation

edited Jan 14, 2015 at 14:04

answered Apr 22, 2013 at 14:17

WiredPrairie

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2 Comments

Rax Wunter Over a year ago

$in takes only arrays: "Can't canonicalize query: BadValue $in needs an array"

WiredPrairie Over a year ago

@RaxWunter -- correct. Not sure why I had that as I did confirm it behaves that way as of 2.6. Thanks! (This was from April 2013 so something may changed in the console or DB ... not sure what happend :) )

Joshua · Accepted Answer · 2014-07-03 19:02:12Z

5

If you're simply looking to match all documents with an array containing a given value, you can just specify the value on the reference to that array, e.g.

db.mycodes.find( { code: '001' } )

Which thus would return you all documents that contained '001' in their code array

answered Jul 3, 2014 at 19:02

Joshua

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