Currently there is no way to grab contained collections in a single select
(and I have extreme doubts that it would be a performance increase unless
access to the database is over a slow network). A much better approach in
most cases is to make the Map lazy.
(For contained collections of _entities_, you can use a Hibernate query.)
Philipp Meier
<[EMAIL PROTECTED]> To: hibernate list <[EMAIL
PROTECTED]>
Sent by: cc:
[EMAIL PROTECTED] Subject: [Hibernate] Performance of
"nested relations"
eforge.net
19/02/03 04:55 AM
Hello,
i have the following situation:
Group -- 1:n --> Recipient, Recipient has a property of type java.util.Map
Everything works fine, but loading the list of recipients is terribly slow
because hibernate executes an sql query for each recipient to load the
recipients's map. The logfiles look like the following:
[..]
Hibernate: SELECT recip0_.value as value, recip0_.field as field FROM
recipient_values recip0_ WHERE recip0_.id=?
Hibernate: SELECT recip0_.value as value, recip0_.field as field FROM
Hibernate: SELECT recip0_.value as value, recip0_.field as field FROM
recipient_values recip0_ WHERE recip0_.id=?
recipient_values recip0_ WHERE recip0_.id=?
[..]
Is there a way that hibernate execute _one_ sql statement to load _all_
recipient_values for the recipients related to the Group? Or is there a
better design over all?
This are the mappings I currently use:
-- Recipient
<hibernate-mapping>
<class name="Recipient">
<id name="id" type="long">
<generator class="native"/>
</id>
<map name="values" table="recipient_values">
<key column="id"/>
<index column="field" type="java.lang.String"/>
<element column="value" type="java.lang.String"/>
</map>
<many-to-one name="group" class="Group" column="group_" not-null
="true"/>
</class>
</hibernate-mapping>
-- Group
<hibernate-mapping>
<class name="Group" table="Group_">
<id name="id" type="long">
<generator class="native"/>
</id>
<property name="name" type="java.lang.String"/>
<set name="recipients" inverse="true" cascade="all" >
<key column="group_"/>
<one-to-many class="Recipient"/>
</set>
</class>
</hibernate-mapping>
Thanks,
-billy.
--
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eLösungen 89077 Ulm Fax: +49-731-399 499-9
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