Question

I have a simple jpa entity ‘ApplicationForm’ with a one to many list in it:

 @OneToMany(cascade=CascadeType.REMOVE, mappedBy="textQuestion")
 private List<Dictionary> questions;

The variable Dictionary contained in ApplicationForm is just another plain entity with just the text of the question.
The corresponding database table mapped by Dictionary is:

'locale' 'text'      'formId'
en       my question 123 
it       mia domanda 123

I was wondering if it’s possible with jpa or hibernate, to build a query for retrieving an ApplicationForm entity with a Dictionary for a specific locale, for example ‘it’ only.
That would be easy enough to do with standard sql, but I cannot translate in hql.

If not possible, could you suggest an alternative way ? I have tried to manually iterate the Dictionary questions list and remove the not required locale, but is not really elegant, and also I got a jpa/hibernate error.

I hope I made myself clear, and code supplied is enough.

thanks

Answer 1

I was wondering if it’s possible with jpa or hibernate, to build a query for retrieving an ApplicationForm entity with a Dictionary for a specific locale, for example ‘it’ only.

Not with standard JPA. But Hibernate allows to apply arbitrary filters to a collection load during a given session. From the Hibernate Annotations Reference Guide:

2.4.8. Filters

Hibernate has the ability to apply
arbitrary filters on top of your data.
Those filters are applied at runtime
on a given session. First, you need to
define them.

@org.hibernate.annotations.FilterDef
or @FilterDefs define filter
definition(s) used by filter(s) using
the same name. A filter definition has
a name() and an array of
parameters(). A parameter will allow
you to adjust the behavior of the
filter at runtime. Each parameter is
defined by a @ParamDef which has a
name and a type. You can also define a
defaultCondition() parameter for a
given @FilterDef to set the default
condition to use when none are defined
in each individual @Filter. A
@FilterDef(s) can be defined at the
class or package level.

We now need to define the SQL filter
clause applied to either the entity
load or the collection load. @Filter
is used and placed either on the
entity or the collection element

@Entity
@FilterDef(name="minLength", parameters=@ParamDef( name="minLength", type="integer" ) )
@Filters( {
    @Filter(name="betweenLength", condition=":minLength <= length and :maxLength >= length"),
    @Filter(name="minLength", condition=":minLength <= length")
} )
public class Forest { ... }

When the collection use an association
table as a relational representation,
you might want to apply the filter
condition to the association table
itself or to the target entity table.
To apply the constraint on the target
entity, use the regular @Filter
annotation. However, if you wan to
target the association table, use the
@FilterJoinTable annotation.

@OneToMany
@JoinTable
//filter on the target entity table
@Filter(name="betweenLength", condition=":minLength <= length and :maxLength >= length")
//filter on the association table
@FilterJoinTable(name="security", condition=":userlevel >= requredLevel")
public Set<Forest> getForests() { ... }

See also

• Chapter 17. Filtering data In the Hibernate Core Reference Documentation.
• Hibernate3 Filters