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14.4. Associations and Joins

You can also assign aliases to associated entities or to elements of a collection of values using a join. For example:

from Cat as cat
    inner join cat.mate as mate
    left outer join cat.kittens as kitten

from Cat as cat
    inner join cat.mate as mate
    left outer join cat.kittens as kitten

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

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

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from Formula form full join form.parameter param

from Formula form full join form.parameter param

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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

from Cat as cat
    join cat.mate as mate
    left join cat.kittens as kitten

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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

from Cat as cat
    left join cat.kittens as kitten
        with kitten.bodyWeight > 10.0

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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.

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

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

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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

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

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Important

The fetch construct cannot be used in queries called using iterate() (though scroll() can be used). Fetch should not 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.

If you are using property-level lazy fetching (with bytecode instrumentation), it is possible to force Hibernate to fetch the lazy properties in the first query immediately using fetch all properties.

from Document fetch all properties order by name

from Document fetch all properties order by name

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from Document doc fetch all properties where lower(doc.name) like '%cats%'

from Document doc fetch all properties where lower(doc.name) like '%cats%'

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14.4. Associations and Joins

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