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Does outer-join attribute have any impact on HQL queries

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mat56

Post subject: Does outer-join attribute have any impact on HQL queries

Posted: Fri Sep 09, 2005 6:28 am

Could anyone confirm if many-to-one associations should be resolved by Nhibernate using a single query with joins when outer-join is set to true?

To make it clear, I have the following simple mapping:

Code:

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0">
      <class name="SimpleTest.Deal, SimpleTest" table="DEA_DEAL">
      <id name="DealID" column="DEA_ID" type="Int32" unsaved-value="0">
         <generator class="sequence">
            <param name="sequence">DEA_SEQ</param>
         </generator>
      </id>
      <property name="Date" type="DateTime" column="DEA_DT" />
            <many-to-one name="AccountingPortfolio" class="SimpleTest.Portfolio, SimpleTest"
         column="DEA_ID_APRF" outer-join="true"/>
      <many-to-one name="TradingPortfolio" class="SimpleTest.Portfolio, SimpleTest"
         column="DEA_ID_TPRF" outer-join="true"/>
      <many-to-one name="Instrument" class="SimpleTest.GenericInstrument, SimpleTest" column="DEA_ID" outer-join="true"/>
   </class>
   <class name="SimpleTest.GenericInstrument, SimpleTest" table="DEA_INSTRUMENT">
      <id name="InstrumentID" column="ITR_ID" type="Int32" unsaved-value="0">
         <generator class="sequence">
            <param name="sequence">ITR_SEQ</param>
         </generator>
      </id>
            <many-to-one name="TradingPortfolio" class="SimpleTest.Portfolio, SimpleTest"
         column="ITR_ID_TPRF" />
      <bag name="InstrumentSequence" inverse="false" lazy="true" order-by="ITR_ID" where="ITR_DTDELETE = to_date('01013000', 'ddmmyyyy')" >
         <key column="ITR_ID_ITR" />
         <one-to-many class="SimpleTest.GenericInstrument, SimpleTest"/>
      </bag>
   </class>
      <class name="SimpleTest.Portfolio, SimpleTest" table="PTF_PORTFOLIO" where="PTF_DTDELETE = to_date('01013000', 'ddmmyyyy')" mutable="false">
      <id name="Id" column="PTF_ID" type="Int32" unsaved-value="0">
         <generator class="sequence">
            <param name="sequence">PRF_SEQ</param>
         </generator>
      </id>
      <property name="Code" type="String" column="PTF_CD" />
      <property name="Name" type="String" column="PTF_NAME" />
      <property name="DeleteDate" column="PTF_DTDELETE" type="DateTime"/>
      <property name="UpdateDate" column="PTF_LASTUPD" type="DateTime"/>
   </class>
</hibernate-mapping> 

when I run the following HQL: "from Deal"
I would expect the portfolio and instrument to be loaded in a single select, but nhibernate keeps running several selects to resolve the many-to-one associations. Is that a normal behavior?

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sergey

Post subject:

Posted: Fri Sep 09, 2005 7:38 am

Contributor

Joined: Wed May 11, 2005 4:59 pm
Posts: 1766
Location: Prague, Czech Republic

From Hibernate FAQ:

Quote:

Hibernate ignores my outer-join="true" setting and fetches an association lazily, using n+1 selects!

HQL queries always ignore the setting for outer-join defined in the mapping document. This setting applies only to associations fetched using get() or load(), Criteria queries, and graph navigation. If you need to enable eager fetching for a HQL query, use an explicit LEFT JOIN FETCH.

Note also that Hibernate 2.x does not support outer join fetching of more than one many-valued association in the same query. Hibernate 3.x allows you to create Cartesian products, even if they are slower than two separate queries.

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