Re: complex query vs performIteratedQuery vs Prefetching

From: Hans Pikkemaat (h.pikkemaa..si-solutions.nl)
Date: Tue Nov 10 2009 - 08:12:22 EST

  • Next message: Andrey Razumovsky: "Re: complex query vs performIteratedQuery vs Prefetching"

    Hi,

    I'll give you some insight in what I tried.

            DataContext dataContext = this.createDataContext();

            String sql = "select ... from table1 join table 2 ...";
            SQLTemplate query = new SQLTemplate(Table1Object.class, sql);
            
    query.addPrefetch(table2.RELATION_PROPERTY).setSemantics(PrefetchTreeNode.JOINT_PREFETCH_SEMANTICS);
            query.setPageSize(1000);

            ResultIterator iterator = dataContext.performIteratedQuery(query);

            while (iterator.hasNextRow()) {
                DataRow dataRow = (DataRow) iterator.nextDataRow();
                Table1Object table1 = (Table1Object)
    dataContext.objectFromDataRow(Table1Object.class, dataRow, false);
                List<Table2Object> list = table1.getTable2Objects();
                for (Table2Object t2o:list) {
                   System.out.println(t2o.getName());
                }
             }

    When the for loop starts and gets the iterator from the list, then a
    separate query is executed, indicating
    that the prefetching didn't work.

    tx

    Hans

    Andrey Razumovsky wrote:
    > Hi,
    >
    > I think the best in your case would be using disjoint prefetching;
    > http://cayenne.apache.org/doc20/prefetching.html
    > This way both table data will be returned altogether (in same db row), so
    > you will be able to iterate though them at the same time.
    >
    > I also highly encourage you to try today-released Cayenne3.0 beta. It proved
    > to be stable and many prefetching (ant other!) improvements were made. Check
    > the main site!
    >
    > 2009/11/10 Hans Pikkemaat <h.pikkemaa..si-solutions.nl>
    >
    >
    >> Hi,
    >>
    >> My case:
    >>
    >> I have a complex query which returns a huge amount of data. It returns data
    >> from
    >> two tables which are joined.
    >>
    >> Because the amount of data is huge I cannot load all of it into memory.
    >> For this reason I want to use an iterated query.
    >>
    >> I also want to prevent cayenne from executing a query for each detail
    >> record
    >> so I want to use prefetching.
    >>
    >> What I tried:
    >>
    >> - I'm using cayenne 2.0.4.
    >> - I use SQLTemplate to instantiate the query.
    >> - I set the page size to 1000 to prevent loading the whole db (required
    >> for postgres)
    >> - I use performIteratedQuery to run the query.
    >> - As I get DataRows back from the iterated query I use
    >> dataContext.objectFromDataRow(..) to create my objects
    >>
    >> The Problem:
    >>
    >> The relation is not automatically setup. This means that for every record
    >> I access the detail table a query is executed.
    >>
    >> My Questions:
    >>
    >> - How should I use prefetching in combination with SQLTemplate and an
    >> iterated query which returns DataRows?
    >> - Is there a way to manually setup this relationship (without changing
    >> the state of the parent object?)
    >> - Is there another way to do what I want using Cayenne?
    >>
    >>
    >
    >
    >
    > 

    -- 
	TSi Solutions
Neptunusstraat 25
7521 WC Enschede

    Tel. +31 (0)88 - 25 00 000
Fax. +31 (0)88 - 25 00 122
Hans Pikkemaat
Java Developer (Services Team)
	E-mail: h.pikkemaa..si-solutions.nl <mailto:h.pikkemaat@tsi-solutions.nl>
  	www.tsi-solutions.nl <http://www.tsi-solutions.nl/>
www.toeristiek.nl <http://www.toeristiek.nl/>
	

    10 jaar TSi Solutions
... marktleider in het automatiseren en outsourcen van werkprocessen in 
de reisbranche
... toonaangevende partij voor het verzamelen, structureren en 
beschikbaarstellen van reiscontent
... Reisrevue Innovatieveer 2008 - Veervolle vermelding
... Winnaar Reisrevue Innovatieveer 2009
... Top 20 positie in 2008 Deloitte Technology Fast50 Nederland
... Top 10 positie in 2009 Deloitte Technology Fast50 Benelux
... genomineerd voor Technology 500 EMEA 2009
TSi Solutions is de handelsnaam van Travel Service International 
b.v.[KvK 06091935]
DISCLAIMER: De informatie opgenomen in dit bericht kan vertrouwelijk 
zijn en is uitsluitend bestemd voor de geadresseerde.
Indien u dit bericht onterecht ontvangt, wordt u verzocht de inhoud niet 
te gebruiken en de afzender direct te informeren door het bericht te 
retourneren.
The information contained in this message may be confidential and is 
intended to be exclusively for the addressee.
Should you receive this message unintentionally, please do not use the 
contents herein and notify the sender immediately by return e-mail.

    This archive was generated by hypermail 2.0.0 : Tue Nov 10 2009 - 08:13:00 EST