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From "Jeff Butler" <jeffgbut...@gmail.com>
Subject Re: how to map huge resultsets?
Date Thu, 04 Oct 2007 12:15:02 GMT
Your question is not that confusing.  Here are the answers:

1. No (although the approach suggested by Christopher Lamey is *very* close
if you are willing to shift your paradigm)

2. If the result set is truly huge, then approach #1 is a bad idea because
iBATIS will have to read through huge amounts of data to get to the latter
parts of the result set in subsequent calls (this is why Larry asked about
selecting by primary key rather than returning such a huge result set)

I guess you'll have to stick with Hibernate :)

Jeff Butler


On 10/4/07, robert.kasanicky@accenture.com <robert.kasanicky@accenture.com>
wrote:
>
> Seems like my question was quite confusing, so I'll try to explain what
> I need once again from scratch.
>
> 1. I need to process a potentially huge number of rows (so
> queryForList(query) is not an option because it would try to load all
> objects into memory at once).
>
> 2. I need to control the iteration over the query results, so I can't
> use queryWithRowHandler (in this case iBATIS iterates and I only tell
> iBATIS how each record should be processed - I need to be able to ask
> iBATIS for the next record instead - it is the internal vs. external
> iterator difference, or SAX vs. StAX in case of XML processing or how
> collections are typically iterated in ruby/groovy vs. Java or ... you
> name it). Simply framework iterates, iBATIS knows the query and must
> provide next record when it is asked for it.
>
> First approach:
> It is possible to implement these requirements by using
> queryForList(query, skipSize, maxSize) and  query the database
> TOTAL_ROW_COUNT / maxSize times (issuing a new query when records from
> current list have been processed - this is invisible to the user
> (framework) who just iteratively asks for next record for processing).
>
> Second approach:
> Hibernate allows to get a ScrollableResults object for a query allowing
> the user to move the cursor and ask for an object that corresponds to
> the current row.
>
> Questions:
> 1. is the second approach possible with iBATIS?
> 2. first vs. second approach pros & cons?
>
> Thanks
> Robert
>
> -----Original Message-----
> From: larry.meadors@gmail.com [mailto:larry.meadors@gmail.com] On Behalf
> Of Larry Meadors
> Sent: Thursday, October 04, 2007 01:18
> To: user-java@ibatis.apache.org
> Subject: Re: how to map huge resultsets?
>
> I'm confused, how would grabbing chunks of a huge result set be more
> efficient than grabbing the records by PK?
>
> Couldn't you just have a select that grabbed the requested item, and
> passed it back to the consumer?
>
> Larry
>
>
> On 10/3/07, robert.kasanicky@accenture.com
> <robert.kasanicky@accenture.com> wrote:
> > My problem with RowHandler is that iBATIS controls the iteration. I
> just say
> >
> > sqlMap.queryWithRowHandler ("getAllItems", rowHandler);
> >
> > and all items get processed by the rowHandler.
> >
> > But in my case I need to make iBATIS return items one-by-one when it
> is asked to do so because the framework controls the iteration.
> > This is a very simplified basic logic of the framework:
> >
> > while (itemProvider.hasNext()) {
> >  Object item = itemProvider.next();
> >  process(item);
> > }
> >
> >
> >
> > -----Original Message-----
> > From: Christopher Lamey [mailto:clamey@localmatters.com]
> > Sent: Wed 10/3/2007 11:55 PM
> > To: user-java@ibatis.apache.org
> > Subject: Re: how to map huge resultsets?
> >
> > Hmm...I don't see how having an external framework prevents you from
> using a
> > RowHandler.  Your item provider could implement the RowHandler
> interface and
> > the external code wouldn't know or care about it.  Or your item
> provider
> > could wrap something that does implement RowHandler so the external
> code
> > doesn't know it exists.  The main point is that you can pull mapped
> objects
> > on a row by row basis from the database.
> >
> > How is a RowHandler different that what you were describing in your
> first
> > mail?
> >
> > On 10/3/07 3:33 PM, "robert.kasanicky@accenture.com"
> > <robert.kasanicky@accenture.com> wrote:
> >
> > >
> > > Thanks for your reply.
> > >
> > > I can't use the rowhandler callback because the iteration is
> external to
> > > iBATIS. In my case a batch framework iteratively asks for an item
> and
> > > processes it - and I am trying to implement an iBATIS item provider
> (I realize
> > > now I should have explained this in the initial post).
> > >
> > > Robert
> > >
> > >
> > > -----Original Message-----
> > > From: Christopher Lamey [mailto:clamey@localmatters.com]
> > > Sent: Wed 10/3/2007 11:06 PM
> > > To: user-java@ibatis.apache.org
> > > Subject: Re: how to map huge resultsets?
> > >
> > > Hello,
> > >
> > > You should take a look at the RowHandler interface and the
> > > queryWithRowHandler calls in SqlMapClient (page 61 of the pdf).
> Basically,
> > > the RowHandler gets invoked for every row returned rather than
> mapping all
> > > the rows into objects in a collection.
> > >
> > > Cheers,
> > > Chris
> > >
> > >
> > > On 10/3/07 2:37 PM, "robert.kasanicky@accenture.com"
> > > <robert.kasanicky@accenture.com> wrote:
> > >
> > >> Hello,
> > >>
> > >> I am wondering whether it possible to implement the following
> scenario with
> > >> iBATIS:
> > >>
> > >>    1. run an iBATIS-managed select
> > >>    2. get a scrollable result set instead of a list of mapped
> objects
> > >>    3. manually scroll the result set and ask iBATIS for object
> corresponding
> > >> to current row
> > >>
> > >> Hibernate provides this possibility
> > >> (http://www.hibernate.org/hib_docs/reference/en/html/batch.html) so
> I thought
> > >> it would be feasible with iBATIS too, but I couldn't figure out a
> way. The
> > >> motivation is a batch scenario where the select returns a huge
> number of rows
> > >> so all mapped objects can't be loaded into memory at once.
> > >>
> > >> The iBATIS way I am aware of is to use queryForList(String
> statementName, int
> > >> skipResults, int maxResults), but this means querying the database
> > >> (TOTAL_NUMBER_OF_ROWS / maxResults) times.
> > >>
> > >> Can somebody give advice about pros & cons of the two approaches?
> > >>
> > >> Thanks
> > >> Robert
> > >>
> > >>
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