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Date: Fri, 20 Nov 2009 19:12:24 +0100
From: Sebastien PASTOR <sebastien.pastor@gmx.com>
To: user@couchdb.apache.org
Subject: Re: Newbie :Filtering using complex key and array
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Thanks again Matt, 

To be honnest i didn't know the group_level parameter.neat !
I understand i would need another view if i wanted to know the count of
restaurant per type only.
But i want both : filter by restaurant type and postal code. In that
regards the solution you gave me works great. So i think my question was
really this : can the reduce function produce the same result without
printing out the postal code since i don t really need it cause all i am interested in is
type of restaurant and number of them in the area specified in the
Query.
I guess at the reduce level this cannot be done but maybe somewhere
else?
As a matter of fact i can live without this  : all i need to do is pick
up key[1] in my JQuery parser to get what i want, but stilli, would be
nice to know whether is is possible to be able to spill out the json
data you want out of a view.

Hope i ve been clearer (and that is nottoo much of a  dumb question )  and
thanx again for your time.

Cheers

Seb


On Fri, Nov 20, 2009 at 03:40:08PM +0000, Matt Goodall wrote:
> 2009/11/20 Sebastien PASTOR <sebastien.pastor@gmx.com>:
> > Thanks for the quick reply Matt,
> >
> > It does sound like a trick because it might generate a much bigger list
> > than i ll have document in the db (times number of delivery areas). But
> > i guess as long as the map index ??is generated only once it will just be
> > a matter of more space used to store the index right?
> 
> Correct. CouchDB's views essentially trade disk space for predictable
> query times (assuming the view is up to date, of course).
> 
> One thing you can do to reduce the size of views, if necessary, is to
> emit a null value, i.e. emit(key, null), and add the include_docs=true
> query parameter when GET'ing the view. See
> http://wiki.apache.org/couchdb/HTTP_view_API#Querying_Options.
> 
> However, that may make things a little slower and put a bit more load
> on CouchDB.  If everything's in the view then CouchDB can jump into
> the view at the startkey and simply stream the view until the endkey.
> With include_docs=true there's another lookup to get the doc per row
> returned by the view.
> 
> I've never measured the performance hit of include_docs, I just know I
> use it quite a lot and haven't worried too much about it so far ;-).
> 
> > I guess this is how things should be
> > handled when using couchDB, not obvious when coming from SQL :)
> 
> Yep, it's quite a different way of thinking about your data.
> 
> > At least it works exactly as expected.One little thing that bugs me is that the reduce function returns :
> >
> > {"rows":[
> > {"key":[75010,"indian"],"value":1},
> > {"key":[75010,"italian"],"value":2},
> > {"key":[75010,"japanese"],"value":1}
> > ]}
> 
> As you've probably discovered, you can get three types of count from
> this view by playing with the view's group_level query param:
> 
> 1. The number of restaurants of each type in a delivery area, e.g.
> italian restaurants in 75010.
> 2. The number of restaurants in a delivery area.
> 3. The total number of restaurants in your database.
> 
> >
> > If i want to return only restaurant type and the number of
> > restaurants
> > Something like :
> > {"key":"italian","value":1},
> >
> > Is it something to could/should be done in Lists or in some way in the
> > reduce function ?
> 
> For this you'll need an additional view. The map would probably
> emit(doc.type, 1) and the reduce would calculate the sum.
> 
> - Matt
> 
> >
> > Thanks again !
> >
> > Sebastien
> >
> > On Fri, Nov 20, 2009 at 12:15:59PM +0000, Matt Goodall wrote:
> >> 2009/11/20 Sebastien PASTOR <sebastien.pastor@gmx.com>:
> >> > Sorry for the previous blank mail ... here is the content :
> >> >
> >> > Hi there,
> >> >
> >> > Pretty new to couchDB. I ve read a lot about couchdb and finally dive
> >> > into it with a small project :)
> >> > I am trying to do a simple thing and i am not sure at all if i am going
> >> > the right way :
> >> >
> >> > my docs look like this :
> >> >
> >> > {
> >> > ??"name":"Pizza Torino",
> >> > ?? "delivery_areas":[75019,75018,75012,75013,75010],
> >> > ?? ?? "type":"italian"
> >> > ?? ?? }
> >> >
> >> > ?? ?? I managed to get ??all shops by type and get a reduce function to
> >> > ?? ?? do the sum ( not much i know but still quite an accomplishment for
> >> > ?? ?? me :) )
> >> > ?? ?? I then tried to get my result filtered by delivery_areas. as in
> >> > ?? ?? getting only shop
> >> > ?? ?? that do delivery in postal code 75019. I just could not ??have
> >> > ?? ?? anything that
> >> > ?? ?? worked using startkey and endkey ... is it the way to go or is
> >> > ?? ?? storing
> >> > ?? ?? delivery_areas within an array not right ?
> >> >
> >> > ?? ?? my last map function looks like this :
> >> > ?? ?? ?? ?? "getShops" : {
> >> > ?? ?? ?? ?? ?? ?? ?? ?? ??"map" : "function(doc){
> >> > ?? ?? ?? ?? ?? ?? ?? ?? emit([doc.delivery_areas,doc.type],doc.name)
> >> > ?? ?? ?? ?? ?? ?? ?? ?? }
> >> > ?? ?? }
> >> >
> >> > ??Thanks for pointing me to the right direction
> >>
> >> Storing a list of delivery areas is good. The "trick" is to emit
> >> multiple rows per document, e.g.
> >>
> >> ?? ?? function(doc) {
> >> ?? ?? ?? for each (area in doc.delivery_areas) {
> >> ?? ?? ?? ?? emit([area, doc.type], doc.name);
> >> ?? ?? ?? }
> >> ?? ?? }
> >>
> >> You can then query with startkey=[75018, null] and endkey=[75018, {}]
> >> to get all restaurants in the 75018 area.
> >>
> >> The null and {} might look a bit weird at first but it's all to do
> >> with how CouchDB orders rows in a view. See
> >> http://wiki.apache.org/couchdb/View_collation#Collation_Specification
> >> for details.
> >>
> >> Hope this helps.
> >>
> >> - Matt
> >