translate sql query into mongodb query - mongodb

Question

I'm trying to grasp the mongodb concepts by translating some of our sql queries into mongo aggregation framework.
I have an sql code:
select dbo.VisitNo(u.id) as visitNo , o.id, o.PatientId, u.VisitDate
from dbo.Observation o
join sbo.ProspectiveFollowUp u on u.rootid = o.Id
order by o.PatientId
The dbo.VisitNo is implemented as:
CREATE FUNCTION dbo.VisitNo(#Id int)
RETURNS INT
AS
BEGIN
DECLARE #VisitDate date, #RootId int
SELECT #VisitDate=VisitDate, #RootId=RootId FROM dbo.ProspectiveFollowUp WHERE Id=#Id
RETURN (SELECT COUNT(1) FROM dbo.ProspectiveFollowUp WHERE RootId = #RootId AND VisitDate <= #VisitDate)
END
result:
My document in Mongo has following structure:
{
"_id",
"values":[
{
"Id",
"PatientId",
"ProspectiveFollowUp":[
"Id",
"RootId",
"VisitDate"
]
}
]
}
The values array has always one element, but that's how the data was imported. ProspectiveFollowUp has at least one record.
Creating query for retrieving the data was rather easy:
db.dbo_ObservationJSON.aggregate([
{ $unwind: '$values' },
{
$project: {
_id: 0,
Id: '$values.Id',
PatientId: '$values.PatientId',
VisitDate: '$values.ProspectiveFollowUp.VisitDate'
}
},
{ $unwind: '$VisitDate' },
{ $sort: { PatientId: 1 } }
])
The harder part is the custom function itself. I can't think outside od tsql world yet, so I have hard time getting this to work. I have translated the function into mongo the following way:
var id = 4
var result = db.dbo.ObservationJSON.aggregate([
{ $unwind: '$values' },
{ $unwind: '$values.ProspectiveFollowUp' },
{ $project: { Id: '$values.ProspectiveFollowUp.Id', RootId: '$values.ProspectiveFollowUp.RootId', VisitDate: '$values.ProspectiveFollowUp.VisitDate', _id:0 }},
{ $match: { Id: id }}
]).toArray()[0]
var totalResult = db.dbo_ObservationJSON.aggregate([{
$unwind: {
path: '$values'
}
}, {
$unwind: {
path: '$values.ProspectiveFollowUp'
}
}, {
$project: {
Id: '$values.ProspectiveFollowUp.Id',
RootId: '$values.ProspectiveFollowUp.RootId',
VisitDate: '$values.ProspectiveFollowUp.VisitDate'
}
}, {
$match: {
RootId: result.RootId,
VisitDate: {
$lte: result.VisitDate
}
}
},{$count: 'total'}]).toArray()[0]
But don't know how to integrate it into the aggregation function above.
Can I write the entire sql query equivalent into one mongo aggregate expression?

Answer 1

I finally got it to work.
db.dbo_ObservationJSON.aggregate([
{ $unwind: '$values' },
{ $unwind: { path: '$values.ProspectiveFollowUp', "includeArrayIndex": "index" } },
{
$project: {
_id: 0,
VisitNo: { $add: ['$index', 1] },
RootId: '$values.ProspectiveFollowUp.RootId',
PatientId: '$values.PatientId',
VisitDate: '$values.ProspectiveFollowUp.VisitDate'
}
},
{
$sort: {
PatientId: 1
}
}
]);