Este conteúdo não está disponível no idioma selecionado.

7.7. The where clause

The where clause allows you to narrow the list of instances returned. If no alias exists, you may refer to properties by name:

select cat from Cat cat where cat.name='Fritz'

select cat from Cat cat where cat.name='Fritz'

Copy to Clipboard

Toggle word wrap

returns instances of Cat named 'Fritz'.

select foo 
from Foo foo, Bar bar
where foo.startDate = bar.date

select foo 
from Foo foo, Bar bar
where foo.startDate = bar.date

Copy to Clipboard

Toggle word wrap

will return all instances of Foo for which there exists an instance of bar with a date property equal to the startDate property of the Foo. Compound path expressions make the where clause extremely powerful. Consider:

select cat from Cat cat where cat.mate.name is not null

select cat from Cat cat where cat.mate.name is not null

Copy to Clipboard

Toggle word wrap

This query translates to an SQL query with a table (inner) join. If you were to write something like

select foo from Foo foo  
where foo.bar.baz.customer.address.city is not null

select foo from Foo foo  
where foo.bar.baz.customer.address.city is not null

Copy to Clipboard

Toggle word wrap

you would end up with a query that would require four table joins in SQL.

The = operator may be used to compare not only properties, but also instances:

select cat, rival from Cat cat, Cat rival where cat.mate = rival.mate

select cat, rival from Cat cat, Cat rival where cat.mate = rival.mate

Copy to Clipboard

Toggle word wrap

select cat, mate 
from Cat cat, Cat mate
where cat.mate = mate

select cat, mate 
from Cat cat, Cat mate
where cat.mate = mate

Copy to Clipboard

Toggle word wrap

The special property (lowercase) id may be used to reference the unique identifier of an object. (You may also use its mapped identifer property name.). Note that this keyword is specific to HQL.

select cat from Cat as cat where cat.id = 123

select cat from Cat as cat where cat.mate.id = 69

select cat from Cat as cat where cat.id = 123

select cat from Cat as cat where cat.mate.id = 69

Copy to Clipboard

Toggle word wrap

The second query is efficient. No table join is required!

Properties of composite identifiers may also be used. Suppose Person has a composite identifier consisting of country and medicareNumber.

select person from bank.Person person
where person.id.country = 'AU' 
    and person.id.medicareNumber = 123456

select person from bank.Person person
where person.id.country = 'AU' 
    and person.id.medicareNumber = 123456

Copy to Clipboard

Toggle word wrap

select account from bank.Account account
where account.owner.id.country = 'AU' 
    and account.owner.id.medicareNumber = 123456

select account from bank.Account account
where account.owner.id.country = 'AU' 
    and account.owner.id.medicareNumber = 123456

Copy to Clipboard

Toggle word wrap

Once again, the second query requires no table join.

Likewise, the special property class accesses the discriminator value of an instance in the case of polymorphic persistence. A Java class name embedded in the where clause will be translated to its discriminator value. Once again, this is specific to HQL.

select cat from Cat cat where cat.class = DomesticCat

select cat from Cat cat where cat.class = DomesticCat

Copy to Clipboard

Toggle word wrap

You may also specify properties of components or composite user types (and of components of components, etc). Never try to use a path-expression that ends in a property of component type (as opposed to a property of a component). For example, if store.owner is an entity with a component address

store.owner.address.city    // okay
store.owner.address         // error!

store.owner.address.city    // okay
store.owner.address         // error!

Copy to Clipboard

Toggle word wrap

An "any" type has the special properties id and class, allowing us to express a join in the following way (where AuditLog.item is a property mapped with <any>). Any is specific to Hibernate

from AuditLog log, Payment payment 
where log.item.class = 'Payment' and log.item.id = payment.id

from AuditLog log, Payment payment 
where log.item.class = 'Payment' and log.item.id = payment.id

Copy to Clipboard

Toggle word wrap

Notice that log.item.class and payment.class would refer to the values of completely different database columns in the above query.

Este conteúdo não está disponível no idioma selecionado.

7.7. The where clause

Aprender

Experimente, compre e venda

Comunidades

Sobre a documentação da Red Hat

Tornando o open source mais inclusivo

Sobre a Red Hat

Theme

Red Hat legal and privacy links

Red Hat legal and privacy links