hi alexey,
don't be upset !
ojb is an or-mapping framework and thus executes more sqls than a manually
coded solution.
in your example ojb should execute 1 sql for articles and 1 sql for EACH
attribute resulting in n + 1 sql for n attributes. the additional count-sqls
are afaik no longer executed.
ojb even provides an optimized way to retrieve all attributes for all
articles in ONE sql, this is called prefetched relationships.
Criteria crit;
crit.addPrefetchedRelationship("parameters"); // add this line to your
query
hth
jakob
----- Original Message -----
From: "Alexey Drougov" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Thursday, January 09, 2003 12:09 PM
Subject: why 1:n relationship produces 2*(n+1) queries ?
> Hello all,
>
> I have two object types: article and attribute for article
>
> repository.xml is as follows:
> ...
> <class-descriptor class="obj.Attribute" table="OBJATTRIBUTE" >
> <field-descriptor id="1" name="objId" column="OBJ" jdbc-type="BIGINT"
> primary-key="true"/>
> <field-descriptor id="2" name="value" column="ATTRIBUTEVALUE"
> jdbc-type="VARCHAR"/>
> </class-descriptor>
> ...
> <class-descriptor class="obj.Article" table="ARTICLE">
> <field-descriptor id="1" name="articleId" column="ID" jdbc-type="BIGINT"
> primary-key="true" />
> <field-descriptor id="2" name="label" column="LABEL" jdbc-type="VARCHAR"
> />
> <collection-descriptor name="parameters"
> element-class-ref="obj.Attribute"
> <inverse-foreignkey field-id-ref="1" />
> </collection-descriptor>
> </class-descriptor>
> ...
>
> Java code is simple:
> ...
> Criteria criteria = new Criteria();
> criteria.addLike("name", "%ab%");
> Query query = QueryFactory.newQuery(Article.class, criteria);
> Collection Ó = broker.getCollectionByQuery(query)
> ...
>
>
> Why this simple example derived from tutorial3 produces 2*(n+1) queries:
>
> // these for articles
> [org.apache.ojb.broker.accesslayer.sql.SqlGeneratorDefaultImpl] DEBUG:
SQL:
> SELECT A0.ID,A0.LABEL FROM ARTICLE A0 WHERE A0.LABEL LIKE ?
>
> // why to queriy count(*) when all rows are
fetched
> anyway ?
> [org.apache.ojb.broker.accesslayer.sql.SqlGeneratorDefaultImpl] DEBUG:
SQL:
> SELECT count(*) FROM ARTICLE A0 WHERE A0.LABEL LIKE ?
>
> // these for every article
> [org.apache.ojb.broker.accesslayer.sql.SqlGeneratorDefaultImpl] DEBUG:
SQL:
> SELECT A0.ATTRIBUTE,A0.ATTRIBUTEVALUE,A0.OBJ FROM OBJATTRIBUTE A0 WHERE
> A0.OBJ = ?
>
> // why to queriy count(*) when all rows are
fetched
> anyway ?
> [org.apache.ojb.broker.accesslayer.sql.SqlGeneratorDefaultImpl] DEBUG:
SQL:
> SELECT count(*) FROM OBJATTRIBUTE A0 WHERE A0.OBJ = ?
>
> [org.apache.ojb.broker.accesslayer.sql.SqlGeneratorDefaultImpl] DEBUG:
SQL:
> SELECT A0.ATTRIBUTE,A0.ATTRIBUTEVALUE,A0.OBJ FROM OBJATTRIBUTE A0 WHERE
> A0.OBJ = ?
> [org.apache.ojb.broker.accesslayer.sql.SqlGeneratorDefaultImpl] DEBUG:
SQL:
> SELECT count(*) FROM OBJATTRIBUTE A0 WHERE A0.OBJ = ?
> ...
>
> perfomance is poor, I'm upset.
>
> How to make OJB make 2 queries: one for Articles, one for corresponding
> Attributes ?
>
>
>
>
>
>
>
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