Inner query using mongo template - mongodb

Question

I am new to MongoDB and Spring mongotemplate. I would like to build a query using mongotemplate whose equivalent in Postgres would be
select * from feedback
where feedback.outletId in (
select outletId from feedback
where feedback.createdOn >= '2013-05-03'::date
)
Is this even possible in MongoDB?

Answer 1

Well there is no concept of inner queries in MongoDB so basically it can be achieved by 2 queries but probably you already know that and want a 'better' solution. Since you asked if it is possible, I think it can be achieved by aggregation however that can be tricky.
db.feedback.aggregate([
{$project : {
'outletId' : 1,
'feedback._id' : '$_id',
'feedback.createdOn' : '$createdOn',
'feedback.a' : '$a'
}},
{$group : {
_id : $outletId,
feedbacks : {$addToSet : '$feedback'}
}},
{$match : {
'feedbacks.createdOn' : {
$gte : ISODate('2013-05-03')}
}},
{$unwind : '$feedback'}]);
You can add one more $project stage in the end to turn child object into values as it was in the document. I know it doesn't look pretty, but I would explain it stage by stage,
first we project a document with putting all the needed field inside a child field called feedback,
in second stage we grouped it by outletId and put all the child feedback into an array named feedbacks,(so for each outletid we get all feedbacks).
in third stage we use $match to filter out where there is not even a single feedback in array which createdOn field is greater than set date,
after those outletIds are filtered out we call unwind to get each child in feedbacks array as a single document.
Now if we talk about mongoTemplate, yes it accepts all these parameter for aggregation including the nesting of child in feedback in first stage. just see some example of TypedAggregation
if you are saving the createdOn field as a string instead of timestamp or ISODate even normal mongo queries won't work on that when you need to find range as its working in your postgres example.
Hope it helps.