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Filter list contained in entity returned by jpa/hibernate query

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

like image 953
Leonardo Avatar asked Jul 21 '10 14:07

Leonardo


1 Answers

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
like image 75
Pascal Thivent Avatar answered Nov 13 '22 01:11

Pascal Thivent