Hi,
It seems that when I set a page size on a regular query with join
prefetching, cayenne
checks if the number of records returned is equal to the page size.
Because the query which is generated contains the DISTINCT keyword
the duplicate entries are removed.
This then causes the exception.
Any idea how to overcome this?
tx
HPI
Hans Pikkemaat wrote:
Hi,
Thanks for your quick response!
I kind of expected that prefetches and iterated queries would not work,
thats the reason for this post :)
I tried the page size on a non iterated query but then I get a weird
exception that I don't
understand:
Exception in thread "main" org.apache.cayenne.CayenneRuntimeException:
[v.2.0.4 October 12 2007] Some ObjectIds are missing from the database.
Expected 10, fetched
8org.apache.cayenne.data...@7fadd3[values={object_id=567},
version=-9223372036854775795, replaces=-9223372036854775808],
org.apache.cayenne.data...@4f1ada[values={object_id=572},
version=-9223372036854775791, replaces=-9223372036854775808]
at
org.apache.cayenne.access.IncrementalFaultList.resolveInterval(IncrementalFaultList.java:396)
at
org.apache.cayenne.access.IncrementalFaultList.get(IncrementalFaultList.java:594)
at
org.apache.cayenne.access.IncrementalFaultList$1.next(IncrementalFaultList.java:508)
at
com.traserv.incrementalsupply.integration.demo.CayenneDemo.doit3(CayenneDemo.java:136)
at
com.traserv.incrementalsupply.integration.demo.CayenneDemo.main(CayenneDemo.java:149)
I cannot forget about data objects because I don't want to query the
detail records separately because of
bad performance (too many single queries).
tx
HPI
Andrey Razumovsky wrote:
Maybe I'm missing something, but i doubt prefetches are implemented
for iterated queries. I would try keeping only setPageSize(1000). It
will do all prefetches and result in same memory payload, because all
datarows in your example are turned into data objects, so they will
all be cached in memory. Smart using query caching would do the trick.
Otherwise, I suggest you forget about data objects in this function of
yours and use only datarows
2009/11/10 Hans Pikkemaat <[email protected]
<mailto:[email protected]>>
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 <[email protected]>
<mailto:[email protected]>
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?
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