Question

I have these 2 mappings:

<hibernate-mapping>
    <class name="sample.Operator" table="OPERATOR">
        <id name="id" >
            <generator class="native" />
        </id>
        <property name="name"  not-null="true">
            <column name="NAME" />
        </property>
        <set name="pointCodes" inverse="false" lazy="true" cascade="save-update">
            <key>
                <column name="OperatorID" />
            </key>
            <one-to-many class="sample.PointCode" />
        </set>
    </class>

<hibernate-mapping>
 <class name="sample.PointCode" table="POINTCODE">
  <id name="id">
   <generator class="native" />
  </id>
  <properties name="pointCodeKey" unique="true">
   <property name="pointCode" not-null="true">
   </property>
   <property name="networkIndicator" not-null="true">
   </property>
  </properties>
  <property name="name" not-null="true">
  </property>
 </class>
  </hibernate-mapping>

Most of the time when featching an Operator I want the pointCodes to be fetched lazily, so I don’t want to set lazy=”false” in the mappings,

However I have one query, e.g. session.createQuery("from Operator").list() where I do want the pointCodes association to NOT be fetched lazily – how do I do that ?

Answer 1

The hibernate reference manual writes:

A “fetch” join allows associations or
collections of values to be
initialized along with their parent
objects using a single select. This is
particularly useful in the case of a
collection. It effectively overrides
the outer join and lazy declarations
of the mapping file for associations
and collections. See Section 20.1,
“Fetching strategies” for more
information.

from Cat as cat
    inner join fetch cat.mate
    left join fetch cat.kittens

A fetch join does not usually need to
assign an alias, because the
associated objects should not be used
in the where clause (or any other
clause). The associated objects are
also not returned directly in the
query results. Instead, they may be
accessed via the parent object. The
only reason you might need an alias is
if you are recursively join fetching a
further collection:

from Cat as cat
    inner join fetch cat.mate
    left join fetch cat.kittens child
    left join fetch child.kittens

The fetch construct cannot be used in
queries called using iterate() (though
scroll() can be used). Fetch should be
used together with setMaxResults() or
setFirstResult(), as these operations
are based on the result rows which
usually contain duplicates for eager
collection fetching, hence, the number
of rows is not what you would expect.
Fetch should also not be used together
with impromptu with condition. It is
possible to create a cartesian product
by join fetching more than one
collection in a query, so take care in
this case. Join fetching multiple
collection roles can produce
unexpected results for bag mappings,
so user discretion is advised when
formulating queries in this case.
Finally, note that full join fetch and
right join fetch are not meaningful.