openjpa-users mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Mark Struberg <strub...@yahoo.de>
Subject Re: Question regarding "constant" parameter replacement in JPQL
Date Tue, 21 Jul 2015 11:17:56 GMT
Oh gosh, just found the following which gets executed _every_ time:

private static boolean isOraclePreparedStatement(Statement stmnt) {
    try {
        return Class.forName("oracle.jdbc.OraclePreparedStatement").
            isInstance(stmnt);
    } catch (Exception e) {
        return false;
    }
}

Please tell me I’m wrong, but we do a Class.forName for _every_ setString on an nchar, etc
field?
Imo we can easily improve this by doing the Class.forName and getField just once and store
it.
There is even a bit more reflection stuff which could get cached imo.

Will create a separate jira for it.

LieGrue,
strub

> Am 20.07.2015 um 16:58 schrieb Kariem Hussein <kariem.hussein@gmail.com>:
> 
> Hi (again),
> 
> I've asked the same question on StackOverflow [1] and was pointed to a
> similar question [2] and actually found the well-hidden option to change
> this behavior by setting the hint UseLiteralInSql to true [3].
> 
> It seems to work, when I set this on the javax.persistence.Query, but it
> does not work, when I set the appropriate hint in orm.xml:
> 
>    <named-query name="person.v">
>      <query>
>        select p
>        from Person p
>        where p.type = 'V'
>      </query>
>      <hint name="openjpa.hint.UseLiteralInSQL" value="true" />
>    </named-query>
> 
> Something wrong with this, or is there a limitation I am running into?
> 
> Thank you very much,
> Kariem
> 
> 
> [1] How can I prevent OpenJPA from replacing “constant” parameters in my
> queries?
> http://stackoverflow.com/questions/31516813
> 
> [2] jpa namedquery with literals changed to prepared statement
> http://stackoverflow.com/questions/28317482
> 
> [3] Javadoc org.apache.openjpa.kernel.QueryHints.HINT_USE_LITERAL_IN_SQL
> http://openjpa.apache.org/builds/2.4.0/apidocs/org/apache/openjpa/kernel/QueryHints.html#HINT_USE_LITERAL_IN_SQL
> 
> On Thu, Jul 16, 2015 at 2:30 PM, Kariem Hussein <kariem.hussein@gmail.com>
> wrote:
> 
>> Hi there,
>> 
>> I am in the process of migrating a big (old) code base from JPA 1 with
>> Hibernate 3.3 to JPA 2 with OpenJPA. I've had a problem with a query that
>> used to work in the old version and now does not and I wanted to know
>> whether my reasoning is correct.
>> 
>> I have already reduced the problem description to the minimal and I hope I
>> did not lose relevant pieces of information on the way.
>> 
>> Given this table in Oracle
>> 
>>    create table PERSON (
>>      id char(10) not null,
>>      type char(3) not null,
>>      primary key (id)
>>    )
>> 
>> There are a lot of rows with in total three different types "WTW", "WAI",
>> "V" (to be honest, I don't know what they stand for). However, we have an
>> entity to work with this table:
>> 
>>    @Entity
>>    public class Person {
>>       String id;
>>       String type;
>>    }
>> 
>> The following query is used in the application from an orm.xml file:
>> 
>>    <named-query name="person.v">
>>      <query>
>>        select p
>>        from Person p
>>        where p.type = 'V'
>>      </query>
>>    </named-query>
>> 
>> As the `type` field is `char(3)`, Oracle will store `V   ` ('V' followed
>> by two spaces) for the string "V".
>> 
>> In Hibernate, I did not have a problem with this query, but with OpenJPA,
>> there is some magic performance improvement on this query that reduces the
>> number of queries by normalizing permutations -- at least that is what I
>> think why my query was translated this way -- which results in the
>> following SQL being sent to the DB
>> 
>>    select p.id, p.type
>>    from PERSON p
>>    where p.type = ?
>> 
>> The "constant" parameter for `type` in my query was replaced with an SQL
>> parameter and the OpenJPA log shows that "V" is passed as value. I believe
>> that because of this replacement I do not get any results anymore.
>> 
>> It works if I do one of the following
>> 
>> - (a) Adapt the JPQL query to `where p.type = 'V  '`, effectively knowing
>> about the underlying `char(3)` field.
>> - (b) Use a native query. OpenJPA will then not try to "improve" my query
>> in a way that changes its semantics.
>> 
>> Is there something I can do to improve this behavior in JPA? Is there any
>> benefit in replacing a "constant" parameter in a named query that is only
>> used in this way (there are no permutations).
>> 
>> Shouldn't the parameter be converted correctly (including padding) into
>> the DB type? Is this a bug, or do I have to specify some kind of hint?
>> 
>> 
>> Thank you for your comments,
>> Kariem
>> 
>> 


Mime
View raw message