Red Hat Summit Red Hat Summitサポートコンソール開発者トライアルの開始お問い合わせ

このコンテンツは選択した言語では利用できません。

14.10. The Where Clause

The where clause allows you to refine the list of instances returned. If no alias exists, you can refer to properties by name: 
from Cat where name='Fritz'
Copy to Clipboard Toggle word wrap
If there is an alias, use a qualified property name: 
from Cat as cat where cat.name='Fritz'
Copy to Clipboard Toggle word wrap
This returns instances of Cat named 'Fritz'.
The following query: 
select foo
from Foo foo, Bar bar
where foo.startDate = bar.date
Copy to Clipboard Toggle word wrap
returns all instances of Foo with 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 the following: 
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. For example: 
from Foo foo
where foo.bar.baz.customer.address.city is not null
Copy to Clipboard Toggle word wrap
would result in a query that would require four table joins in SQL.
The = operator can be used to compare not only properties, but also instances: 
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
Copy to Clipboard Toggle word wrap
The special property (lowercase) id can be used to reference the unique identifier of an object. 
from Cat as cat where cat.id = 123

from Cat as cat where cat.mate.id = 69
Copy to Clipboard Toggle word wrap
The second query is efficient and does not require a table join.
Properties of composite identifiers can also be used. Consider the following example where Person has composite identifiers consisting of country and medicareNumber: 
from bank.Person person
where person.id.country = 'AU'
    and person.id.medicareNumber = 123456
Copy to Clipboard Toggle word wrap 
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 does not require a table join.
Refer to the "Referring to Identifier Property" section for more information regarding referencing identifier properties)
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. 
from Cat cat where cat.class = DomesticCat
Copy to Clipboard Toggle word wrap
You can also use components or composite user types, or properties of said component types.
An "any" type has the special properties id and class that allows you to express a join in the following way (where AuditLog.item is a property mapped with <any>): 
from AuditLog log, Payment payment
where log.item.class = 'Payment' and log.item.id = payment.id
Copy to Clipboard Toggle word wrap
The log.item.class and payment.class would refer to the values of completely different database columns in the above query.
Report a bug
トップに戻る
Red Hat logoGithubredditYoutubeTwitter

詳細情報

試用、購入および販売

コミュニティー

Red Hat ドキュメントについて

Red Hat をお使いのお客様が、信頼できるコンテンツが含まれている製品やサービスを活用することで、イノベーションを行い、目標を達成できるようにします。 最新の更新を見る.

多様性を受け入れるオープンソースの強化

Red Hat では、コード、ドキュメント、Web プロパティーにおける配慮に欠ける用語の置き換えに取り組んでいます。このような変更は、段階的に実施される予定です。詳細情報: Red Hat ブログ.

会社概要

Red Hat は、企業がコアとなるデータセンターからネットワークエッジに至るまで、各種プラットフォームや環境全体で作業を簡素化できるように、強化されたソリューションを提供しています。

Theme

© 2025 Red Hat