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[eclipselink-users] Re: one connection for each request
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Hi Yannick,
the persistence.xml allows to configure a jta-datasource and a
non-jta-datasource.
A possible option is to configure the non-jta-datasource for a
connection pool configuration configured for local transactions.
Non-transactional operations like SELECT statements would be executed
using connections obtained by such non-jta-datasource.
EclipseLink defers write operations by default. All necessary DML
statements will be executed when beforeCompletion() is called by the
transaction service.
The DML statements will be executed using a connection taken from the
jta-datasource.
Typically it more important to share a connection object more
efficiently than to take advantage of keeping affinity of a session or
transaction to a connection.
One reason might by that a session or transaction is repeatedly calling
the very same statement and therefore using the statement cache of a
connection object might have some value.
But do not overestimate the advantage of a statement cache.
As I have stated before the default behavior of EclipseLink is the best
choice in most cases.
Anyway you can also configure eager connections instead of lazy
connections, and you can configure an exclusive connection mode which
allows to use the write connection for reading.
In this case you have to consider transaction isolation and it's impact
on the shared cache.
If you have a support contract for Oracle Application Server, WebLogic
Server or TopLink you can open a service request to discuss your
specific case.
Best regards,
Reinhard
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Today's Topics:
1. Re: Query using WHERE - IN on a Join Table Question (sonavor)
2. Re: Re: one connection for each request (Yannick Majoros)
3. Re: Re: one connection for each request
(Christopher.Mathrusse@xxxxxxxxxx)
4. MySQL batch delete bug (211084) - why so low priority?
(Tobias Marklund)
5. Expression for all lineitems that where picked today
(Philipp Kursawe)
----------------------------------------------------------------------
Message: 1
Date: Fri, 26 Jun 2009 12:53:24 -0700 (PDT)
From: sonavor <jw@xxxxxxxxxxxxxx>
Subject: Re: [eclipselink-users] Query using WHERE - IN on a Join
Table Question
To: eclipselink-users@xxxxxxxxxxx
Message-ID: <24226373.post@xxxxxxxxxxxxxxx>
Content-Type: text/plain; charset=us-ascii
Thanks for the information Chris.
I did try a few tests with the EclipseLink ExpressionBuilder. I was able to
get that to work with a ReadAllQuery but I still had to build the expression
where I am do "OR" operations between the conditions -
Expression exp = null;
ExpressionBuilder eb = new ExpressionBuilder(TestListing.class);
for ( Iterator it=kwList.iterator();it.hasNext(); ) {
TestKeywords tkw = (TestKeywords)it.next();
Expression expKw =
eb.anyOf("testKeywordsCollection").equal(tkw);
if ( exp == null ) {
exp = expKw;
} else {
exp = exp.or(expKw);
}
}
ReadAllQuery readAllQuery = new ReadAllQuery(TestListing.class);
readAllQuery.setSelectionCriteria(exp);
...then get the ActiveSession from the EntityManager and run the query...
I think I will go with the EntityManager.createQuery where I build up the
"OR" operator on the submitted keyword Id values for now.
When EclipseLink 2.0 is available I will retry the "IN" operation. I don't
see a download for EclipseLink 2.0 on the web site.
Christopher Delahunt wrote:
Hello,
IN is supported, but in JPA 1.0, IN cannot take a collection as a
parameter which is why you get an exception.
EclipseLink native expressions have always allowed taking a collection
as a parameter if you are able to build your query that way instead, or
if you can upgrade, support was just added to EclipseLink 2.0 so that
JPQL will also allow taking the collection and is in the more recent
nightly builds (added 2009-06-10 through bug 249224)..
Best Regards,
Chris
sonavor wrote:
I am using Eclipselink and have three tables I am testing. I am
experimenting with have a many-to-many relationship between a main,
listing
table and a keyword table.
The database is MySql.
One table is called TEST_LISTING with these columns -
LISTING_ID integer (PK)
LISTING_NAME varchar(40)
Second table is called TEST_KEYWORDS with these columns -
KW_ID integer (PK)
KW_NAME varchar(24)
Third table is a join table called KW_MAP with these columns -
LISTING_ID integer (PK)
KW_ID integer (PK)
So, using Netbeans 6.1, I generated two JPA entity classes -
TestListing.java
TestKeywords.java
that have a many-to-many relationship to each other via the KW_MAP table.
This all works and I can use a join query like this -
My method receives an ArrayList of Integer values that are the Id of
selected TEST_KEYWORDS called tkwIdArray.
StringBuffer qSB = new StringBuffer();
qSB.append("SELECT t FROM TestListing as t ");
qSB.append("JOIN t.testKeywordsCollection as tkw ");
qSB.append("WHERE ");
for ( int i=0;i<tkwIdArray.length;i++ ) {
Integer tkid = tkwIdArray[i];
if ( i == 0 ) {
qSB.append("tkw.kwId =
:arg").append(String.valueOf(i)).append(" ");
} else {
qSB.append("OR tkw.kwId =
:arg").append(String.valueOf(i)).append(" ");
}
}
Query q = em.createQuery(qSB.toString());
for ( int i=0;i<tkwIdArray.length;i++ ) {
q.setParameter("arg"+String.valueOf(i), tkwIdArray[i]);
}
List<TestListing> tList = q.getResultList();
Although that works I would like to create the query where it looks more
simple by using "IN"
I tried this -
I create a List<Integer> named "idList" that is an ArrayList of the
submitted TEST_KEYWORDS Id values.
List<TestListing> tList = em.createQuery("SELECT t FROM TestListing as t
JOIN t.testKeywordsCollection as tkw WHERE tkw.kwId IN (?1)")
.setParameter(1,
idList).getResultList();
When I try this query I get -
java.lang.IllegalArgumentException: You have attempted to set a value of
type class java.util.ArrayList for parameter 1 with expected type of
class
java.lang.Integer from query string SELECT t FROM TestListing as t JOIN
t.testKeywordsCollection as tkw WHERE tkw.kwId IN (?1).
Does Eclipselink not support using the "IN" attribute in a query?
As a different kind of test I rewrote the join query to find TEST_LISTING
records by joining on the TEST_KEYWORDS.KW_NAME column so I could try the
"IN" with a String Array. I can get the "IN" to work with a hard-coded
String array like -
List<TestListing> tList = em.createQuery("SELECT t FROM TestListing as t
JOIN t.testKeywordsCollection as tkw WHERE tkw.kwName IN
('italian','food')").getResultList();
but when I change it to this -
List<String> kwnList = new ArrayList<String>();
kwnList.add("italian");
kwnList.add("food");
List<TestListing> tList = em.createQuery("SELECT t FROM
TestListing
as t JOIN t.testKeywordsCollection as tkw WHERE tkw.kwName IN (?1)")
.setParameter(1, kwnList).getResultList();
I get the error -
java.lang.IllegalArgumentException: You have attempted to set a value of
type class java.util.ArrayList for parameter 1 with expected type of
class
java.lang.String from query string SELECT t FROM TestListing as t JOIN
t.testKeywordsCollection as tkw WHERE tkw.kwName IN (?1)
Is there a way to do this using Eclipselink or should I just stick with
my
iteration construction of the query using "OR" clauses?
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