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From Jan Lehnardt <...@apache.org>
Subject Re: Views
Date Sat, 26 Apr 2008 19:11:35 GMT
Heya Anthony,
On Apr 26, 2008, at 20:50, Anthony Mills wrote:
> Maybe I missing something.  When you create a view, does it create  
> indexes for attributes in the database?  When you add new documents,  
> do they automatically create the index for the attributes for the  
> view?

A view index only has a single index which is what you send in as the  
first argument in the map() function. Nothing else is going on  
automatically.


> Also, can I call my view with soemthing like ? 
> startkey=['20080403t000000', 1234]&endkey=['20080405t235959', 1234] to
>
> function(doc){
> 	if(doc.type == "hello"){
> 		map([doc.date, doc.number], doc);
> 	}
> }
>
> Then, through the magic of couchdb, I'll only get back those  
> documents between the April 3rd and 5th whose attribute number=1234?

Nope, you'd need a [doc.number, doc.date] index for that. It is rather  
straightforward than magical. The map() function just creates a key- 
value list that is sorted by key and you can query only ranges within  
the key-space.


> Will couchdb only search through records that match the key? or will  
> it need to go through all documents every time I call the view?

To build the view index CouchDB will go through all documents. But  
only once. For documents that change, get deleted or added, CouchDB  
incrementally updates the index. Also, view indexes are build when you  
query the view, not when you add documents.


> To get nerdy, I want my views to find records in O(log n) not O(n).

You get your results in O(1) ;-) (after the first query to each view).

In relational terms, think of a view as an index on a column without  
the write penalty. So have as much as you might need.

I hope that helps, feel free to send more questions :)

Cheers
Jan
--



>
>
> Thanks,
>
> Anthony
>
> On Apr 26, 2008, at 1:02 AM, Chris Anderson wrote:
>
>> Anthony,
>>
>> http://wiki.apache.org/couchdb/ViewCollation is the way to accomplish
>> tasks like that.
>>
>> Christopher Lenz has a write-up of how to use view collation to sort
>> views, achieving comments grouped by parent blog post.
>>
>> http://www.cmlenz.net/archives/2007/10/couchdb-joins
>>
>> In your case you could index a view with date and type, like this
>>
>> [type, date]
>>
>> and then if you had say 5 types you'd do 5 GET queries against the
>> database, each one fetching only the documents for that day.
>>
>> View collation is one of my favorite things about CouchDB. I'm  
>> excited
>> about reduce, because from what I understand, you could use it to
>> lower this to 1 GET, if that's important to you.
>>
>> enjoy,
>> Chris
>>
>> On Fri, Apr 25, 2008 at 9:34 PM, Anthony Mills <amills1037@gascard.net 
>> > wrote:
>>> I read most of the documentation, wiki and blogs, but I still do  
>>> not see how
>>> to accomplish a certain scenario.  Hopefully I can describe it  
>>> adiquitely.
>>>
>>> Lets say I have 1,000,000 documents [all of the same "type"] with  
>>> a date
>>> attribute.  Lets say I want to pick a subset of those documents.   
>>> How can I
>>> pick those documents of one type that fall on one day?  Will I  
>>> need to get
>>> all 1,000,000 documents?  What if I want all documents of one type  
>>> on one
>>> day that match another attribute?
>>>
>>> I pretty sure this is what map/reduce will help with, but is there  
>>> a way to
>>> do this now?  Can you use more documents to build date relations?
>>>
>>> Also, can you pass more variables than just key to
>
>


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