Querying "greater than" in an array

[jgoetzfr]

Hi everyone,

I've developped my first web-application with the powerfull mongodb
but i'm stuck in a final problem.
In my db model, i've got an array listing multiple dates and I'd like
to create a query looking for entries containing one or more dates in
the dates array greater than the on I specified in the querie.

But apparently, mongodb does not allow the "gt" filter on arrays.

Does my problem sounds clear ?
If anyone got an idea...

Many thanks in advance,
Julien

[Tim Rieder]

Given:

> db.a.find()

{ "_id" : ObjectId("4f61110ea472a6f00d6d44c8"), "n" : 1, "x" : [ 1, 2, 3, 4, 5 ] }

{ "_id" : ObjectId("4f611117a472a6f00d6d44c9"), "n" : 2, "x" : [ 2, 1, 3, 5, 4 ] }

{ "_id" : ObjectId("4f611213a472a6f00d6d44ca"), "n" : 1, "x" : [ 1, 2 ] }

Use elemMatch:

> db.a.find({ x:{"$elemMatch":{$gt:3}} })

{ "_id" : ObjectId("4f61110ea472a6f00d6d44c8"), "n" : 1, "x" : [ 1, 2, 3, 4, 5 ] }

{ "_id" : ObjectId("4f611117a472a6f00d6d44c9"), "n" : 2, "x" : [ 2, 1, 3, 5, 4 ] }

Dates should work as well.

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[jgoetzfr]

Thanks Tim ! I'll try this today.

Julien

[Mike]

Hey Tim,

How would this work if your array was an embedded document and you
querying by an element in that doc.

For example

{ "_id" : ObjectId("4f61110ea472a6f00d6d44c8"), "n" : 1, "x" : [ {num:
2}, {num:3},
{num:4}, {num:5} ] }
{ "_id" : ObjectId("4f611117a472a6f00d6d44c9"), "n" : 2, "x" : [ {num:
2}, {num:1}, {num:3},
{num:5}, {num:4} ] }

Thanks,

Mike

[Marc]

Given the following collection:

> db.a.find()
{ "_id" : 1, "n" : 1, "x" : [ { "num" : 1 }, { "num" : 2 }, { "num" :
3 } ] }
{ "_id" : 2, "n" : 2, "x" : [ { "num" : 2 }, { "num" : 3 }, { "num" :
5 } ] }

You can find the document whose "x" array contains an embedded
document containing a value of "num" greater than 4 by using dot
notation:

> db.a.find({"x.num":{$gt:4}})
{ "_id" : 2, "n" : 2, "x" : [ { "num" : 2 }, { "num" : 3 }, { "num" :
5 } ] }

The documentation on querying embedded documents with Mongo may be
found here:
http://www.mongodb.org/display/DOCS/Dot+Notation+%28Reaching+into+Objects%29

The above link also contains a section on how the $elemMatch operator
may be used in a similar situation.

Documentation on $gt and other operators can be found in the "Advanced
Queries" documentation:
http://www.mongodb.org/display/DOCS/Advanced+Queries

Hopefully the above will help you to make your desired queries. If
you have any additional questions, the Mongo Community is here to help!