Kiril,
Thanks for your answer. If I understand list functions correctly they can
transform a view, which will allow me to hone in on the information I need
within one of my views, but I will still need 3 different views and some
external processing to put together all the information that I need? Or do
you mean that I can use the list function to load the results into memory
and perform all my computation within the list function, simply iterating
over my documents various times. Something like:
{ "_id": "_design/roomsharetimes",
"lists": {
"gettimes": "function(head, req) {
var allEvents = []
while(row = getRow()) {
allEvents[allEvents.length] = row;
}
result = doAllMyProcessing(allEvents);
asHTML(result);
}"
}
"views": {
"enterleaveevents": {
"map": "function(doc) {
if (doc.event && (doc.event.type == "enter" || doc.event.type ==
"leave"))
{ emit([doc.event, doc.room, doc.person, doc.timestamp], null); }
}"
}
}
}
This *should* work (haven't tried it yet), but I am doing the bulk of the
work outside the actual view.
Cheers,
Andrew
-----Original Message-----
From: Kiril Stankov [mailto:[email protected]]
Sent: 25 February 2015 18:49
To: [email protected]
Subject: Re: How to query a view from within another view?
Andrew,
it is not possible to query a view from another view.
However, there is a List function, which you can feed with params from the
query.
So, if you have some results from the first view, you can then another view
with a List function that gets some input.
Have a look here:
<http://guide.couchdb.org/draft/transforming.html>
http://guide.couchdb.org/draft/transforming.html
------------------------------------------------------------------------
*With best regards,*
Kiril Stankov
On 25-Feb-15 3:43 PM, Andrew Koster wrote:
> Dear all,
>
> I have a CouchDB database with the following type of documents,
> representing events that happen:
>
> { person: 1
>
> timestamp: 1
>
> event: { type: enter
>
> room: b }
>
> }
>
> and
>
> { person: 2
>
> timestamp: 5
>
> event: { type: leave
>
> room: b }
>
> }
>
> Now the problem that I want to solve is the following: I want to know
> the total amount of time that every other person spent in the same
> room as person 1, at the end of the day when all persons have left all
> rooms. Note that any person can enter and leave many rooms at many
> different times. I honestly don't know whether MapReduce is the best
> paradigm for this, or if I should just export my data and write a
> separate script to figure this stuff out (although this is probably
> not a feasible solution for our production environment).
>
> As a starting solution lets assume that all the data is sane, and thus
> someone entering a room will also leave that room at a later time.
> However, in a final solution this requirement will probably have to be
> relaxed, because some events may be missing.
>
> I have thought of a potential solution, but I have no idea whether
> this is at all possible or how to do this in couchdb. Here is an outline.
>
> 1. Create a view that emits the following format, for every person
> entering a room event:
>
> { [room, person, timestamp], null }
>
> 2. Create a view that emits { [room, timestamp], null} for every time
> person 1 exits the room (could be for all people, but is unnecessary).
>
> 3. Create a view that for each exiting a room event for any person
except
> person 1, does the following. In the mapping step:
>
> . Queries the first view to find the last timestamp when that
person
> entered the room.
>
> . Queries the first view to find all times before the exiting the
> room event that person 1 entered that room
>
> . For each of those times, queries the second view to find all
exit
> times for that room, and for each interval checks what the overlap is.
>
> . Sum these overlaps together and emit as { person, time }
>
> Reduce: for every person, sum all the times together.
>
> However, this relies on me being able to figure out how to query a
> different view from within a view. Does anybody know if that is
> possible, and if so, how?
>
> Kind regards,
>
> Andrew Koster
>
>
>
>
