14.3. Associations and joins

We may also assign aliases to associated entities, or even to elements of a collection of values, using a join.
from Cat as cat
    inner join cat.mate as mate
    left outer join cat.kittens as kitten
from Cat as cat left join cat.mate.kittens as kittens
from Formula form full join form.parameter param
The supported join types are borrowed from ANSI SQL
  • inner join
  • left outer join
  • right outer join
  • full join (not usually useful)
The inner join, left outer join and right outer join constructs may be abbreviated.
from Cat as cat
    join cat.mate as mate
    left join cat.kittens as kitten
You may supply extra join conditions using the HQL with keyword.
from Cat as cat
    left join cat.kittens as kitten
        with kitten.bodyWeight > 10.0
In addition, 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 19.1, “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). Also, the associated objects are not returned directly in the query results. Instead, they may be accessed via the parent object. The only reason we might need an alias is if we 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
Note that the fetch construct may not be used in queries called using iterate() (though scroll() can be used). Nor should fetch 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'd expect. Nor may fetch be used together with an ad hoc 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 also sometimes gives unexpected results for bag mappings, so be careful about how you formulate your queries in this case. Finally, note that full join fetch and right join fetch are not meaningful.
If you are using property-level lazy fetching (with bytecode instrumentation), it is possible to force Hibernate to fetch the lazy properties immediately (in the first query) using fetch all properties.
from Document fetch all properties order by name
from Document doc fetch all properties where lower(doc.name) like '%cats%'