Fetch Month from ISODate MongoDB

[sh]

Hi,

When i  try to  query something on month for ISODate() 

db.xxx.find({$where: function() { return 'personalInfo.dateOfBirth.getMonth()' == 8 ;}} ); it returns me nothing but when i query as below 

db.xxx.find({ $where: "ISODate(\"1900-09-14T00:00:00Z\").getMonth() == 8"}).count()  i get the count back.

can you please help on how to fetch the month & compare it. the dateOfBirth format is "dateOfBirth" : ISODate("1900-09-14T00:00:00Z")

Thanks

Sh

[Will Berkeley]

Don't use $where at all. If you want to query for birthdays in September, use aggregation and $month:

db.xxx.aggregate([

    { "$project" : { "birthMonth" : { "$month" : "$personalInfo.dateOfBirth" } } },

    { "$match" : { "birthMonth" : 9 } }  // note $month returns dates with Jan = 1, not Jan = 0 like .getMonth

])

Ideally, you'd have a $match stage using an index at the start of the pipeline to avoid projecting the birthMonth field for every document. If this is a query you need to do all the time, I'd suggest adding a birthMonth field to the documents (and indexing it), so you can just write something like

db.xxx.find({ "personalInfo.birthMonth" : 9 })

-Will

[sh]

thank you will but when i try the below aggregate i am getting following error 

Error: Printing Stack Trace

    at printStackTrace (src/mongo/shell/utils.js:37:15)

    at DBCollection.aggregate (src/mongo/shell/collection.js:897:9)

    at (shell):1:19

Wed Jan  7 18:53:59.666 JavaScript execution failed: aggregate failed: {

        "errmsg" : "exception: can't convert from BSON type EOO to Date",

        "code" : 16006,

        "ok" : 0

 db.xxx.aggregate([{ "$project" : {"birthMonth" : {"$month" : "$personalInfo.dateOfBirth"}}},{ "$match" : { "birthMonth" : 9 } }])

[sh]

Got it working some fileds were empty so added another condition to it .

 db.xxx.aggregate([{$match: {"Id":"2408"}},{"$project" : { "birthMonth" : { "$month" : "$personalInfo.dateOfBirth" } } },{ "$match" : { "birthMonth" : 9 } }])

Can you please point out to be why the where clause is not working in my below query.

db.xxx.find({$where: function() { return 'personalInfo.dateOfBirth.getMonth()' == 8 ;}} ); it returns me nothing but when i query as below 

[Will Berkeley]

I'd rather not, because you should avoid using $where when there are other options...but the problem is that you need to reference the document using this and not make the body of the return statement be a string:

db.xxx.find({ "$where" : function() { return this.personalInfo.dateOfBirth.getMonth() == 8 } } )

-Will

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