http://docs.jboss.org/hibernate/entitymanager/3.5/reference/en/html/queryhql.html

 

 

Chapter 8. JP-QL: The Object Query Language



8.1. Case Sensitivity 8.2. The from clause 8.3. Associations and joins 8.4. The select clause 8.5. Aggregate functions 8.6. Polymorphic queries 8.7. The where clause 8.8. Expressions 8.9. The order by clause 8.10. The group by clause 8.11. Subqueries 8.12. JP-QL examples 8.13. Bulk UPDATE & DELETE Statements 8.14. Tips & Tricks



The Java Persistence Query Language (JP-QL) has been heavily inspired by HQL, the native Hibernate Query Language. Both are therefore very close to SQL, but portable and independent of the database schema. People familiar with HQL shouldn't have any problem using JP-QL. In fact HQL is a strict superset of JP-QL and you use the same query API for both types of queries. Portable JPA applications however should stick to JP-QL.



Note

For a type-safe approach to query, we highly recommend you to use the Criteria query, seeChapter 9, Criteria Queries.



8.1. Case Sensitivity



Queries are case-insensitive, except for names of Java classes and properties. So SeLeCT is the same assELEct is the same as SELECT but org.hibernate.eg.FOO is not org.hibernate.eg.Foo and foo.barSet is notfoo.BARSET.

This manual uses lowercase JP-QL keywords. Some users find queries with uppercase keywords more readable, but we find this convention ugly when embedded in Java code.



8.2. The from clause



The simplest possible JP-QL query is of the form:



select c from eg.Cat c



which simply returns all instances of the class eg.Cat. Unlike HQL, the select clause is not optional in JP-QL. We don't usually need to qualify the class name, since the entity name defaults to the unqualified class name (@Entity). So we almost always just write:



select c from Cat c



As you may have noticed you can assign aliases to classes, the as keywork is optional. An alias allows you to refer to Cat in other parts of the query.



select cat from Cat as cat



Multiple classes may appear, resulting in a cartesian product or "cross" join.



select from, param from Formula as form, Parameter as param



It is considered good practice to name query aliases using an initial lowercase, consistent with Java naming standards for local variables (eg. domesticCat).



8.3. Associations and joins



You may also assign aliases to associated entities, or even to elements of a collection of values, using ajoin.



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



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



The supported join types are borrowed from ANSI SQL



  • inner join
  • left outer join



The inner join, left outer join constructs may be abbreviated.



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



In addition, 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 fetching options in the associations and collection mapping metadata. See the Performance chapter of the Hibernate reference guide for more information.



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



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). Also, the associated objects are not returned directly in the query results. Instead, they may be accessed via the parent object. The only reason we might need an alias is if we are recursively join fetching a further collection:



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



Note that the fetch construct may not be used in queries called using scroll() or iterate(). Nor should fetchbe used together with setMaxResults() or setFirstResult(). It is possible to create a cartesian product by join fetching more than one collection in a query (as in the example above), be careful the result of this product isn't bigger than you expect. Join fetching multiple collection roles gives unexpected results for bag mappings as it is impossible for Hibernate to differentiate legit duplicates of a given bag from artificial duplicates created by the multi-table cartesian product.

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



select doc from Document doc fetch all properties order by doc.name



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



8.4. The select clause



The select clause picks which objects and properties to return in the query result set. Consider:



select mate from Cat as cat inner join cat.mate as mate



The query will select mates of other Cats. Actually, you may express this query more compactly as:



select cat.mate from Cat cat



Queries may return properties of any value type including properties of component type:



select cat.name from DomesticCat cat where cat.name like 'fri%'



select cust.name.firstName from Customer as cust



Queries may return multiple objects and/or properties as an array of type Object[],



select mother, offspr, mate.name from DomesticCat as mother inner join mother.mate as mate left outer join mother.kittens as offspr



or as a List (HQL specific feature)



select new list(mother, offspr, mate.name) from DomesticCat as mother inner join mother.mate as mate left outer join mother.kittens as offspr



or as an actual type-safe Java object (often called a view object),



select new Family(mother, mate, offspr) from DomesticCat as mother join mother.mate as mate left join mother.kittens as offspr



assuming that the class Family has an appropriate constructor.

You may assign aliases to selected expressions using as:



select max(bodyWeight) as max, min(bodyWeight) as min, count(*) as n from Cat cat



This is most useful when used together with select new map (HQL specific feature):



select new map( max(bodyWeight) as max, min(bodyWeight) as min, count(*) as n ) from Cat cat



This query returns a Map from aliases to selected values.



8.5. Aggregate functions



HQL queries may even return the results of aggregate functions on properties:



select avg(cat.weight), sum(cat.weight), max(cat.weight), count(cat) from Cat cat



The supported aggregate functions are



  • avg(...), avg(distinct ...), sum(...), sum(distinct ...), min(...), max(...)
  • count(*)
  • count(...), count(distinct ...), count(all...)



You may use arithmetic operators, concatenation, and recognized SQL functions in the select clause (dpending on configured dialect, HQL specific feature):



select cat.weight + sum(kitten.weight) from Cat cat join cat.kittens kitten group by cat.id, cat.weight



select firstName||' '||initial||' '||upper(lastName) from Person



The distinct and all keywords may be used and have the same semantics as in SQL.



select distinct cat.name from Cat cat select count(distinct cat.name), count(cat) from Cat cat



8.6. Polymorphic queries



A query like:



select cat from Cat as cat



returns instances not only of Cat, but also of subclasses like DomesticCat. Hibernate queries may nameany Java class or interface in the from clause (portable JP-QL queries should only name mapped entities). The query will return instances of all persistent classes that extend that class or implement the interface. The following query would return all persistent objects:



from java.lang.Object o // HQL only



The interface Named might be implemented by various persistent classes:



from Named n, Named m where n.name = m.name // HQL only



Note that these last two queries will require more than one SQL SELECT. This means that the order byclause does not correctly order the whole result set. (It also means you can't call these queries usingQuery.scroll().)



8.7. 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'



returns instances of Cat named 'Fritz'.



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



will return all instances of Foo for which there exists an instance of bar with a date property equal to thestartDate 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



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



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



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



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



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



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 componentaddress



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



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



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



8.8. Expressions



Expressions allowed in the where clause include most of the kind of things you could write in SQL:



  • mathematical operators +, -, *, /
  • binary comparison operators =, >=, <=, <>, !=, like
  • logical operations and, or, not
  • Parentheses ( ), indicating grouping
  • in, not in, between, is null, is not null, is empty, is not empty, member of and not member of
  • exists, all, any, some (taking subqueries)
  • "Simple" case, case ... when ... then ... else ... end, and "searched" case, case when ... then ... else ... end
  • string concatenation ...||... or concat(...,...) (use concat() for portable JP-QL queries)
  • current_date(), current_time(), current_timestamp()
  • second(...), minute(...), hour(...), day(...), month(...), year(...), (specific to HQL)
  • Any function or operator: substring(), trim(), lower(), upper(), length(), locate(), abs(), sqrt(), bit_length()
  • coalesce() and nullif()
  • TYPE ... in ..., where the first argument is an identifier variable and the second argument is the subclass to restrict polymorphism to (or a list of subclasses surrounded by parenthesis)
  • cast(... as ...), where the second argument is the name of a Hibernate type, and extract(... from ...) if ANSI cast() and extract() is supported by the underlying database
  • Any database-supported SQL scalar function like sign(), trunc(), rtrim(), sin()
  • JDBC IN parameters ?
  • named parameters :name, :start_date, :x1
  • SQL literals 'foo', 69, '1970-01-01 10:00:01.0'
  • JDBC escape syntax for dates (dependent on your JDBC driver support) (eg.where date = {d '2008-12-31'})
  • Java public static final constants eg.Color.TABBY



in and between may be used as follows:



select cat from DomesticCat cat where cat.name between 'A' and 'B'



select cat from DomesticCat cat where cat.name in ( 'Foo', 'Bar', 'Baz' )



and the negated forms may be written



select cat from DomesticCat cat where cat.name not between 'A' and 'B'



select cat from DomesticCat cat where cat.name not in ( 'Foo', 'Bar', 'Baz' )



Likewise, is null and is not null may be used to test for null values.

Booleans may be easily used in expressions by declaring HQL query substitutions in Hibernate configuration:



hibernate.query.substitutions true 1, false 0



This will replace the keywords true and false with the literals 1 and 0 in the translated SQL from this HQL:



select cat from Cat cat where cat.alive = true



You may test the size of a collection with the special property size, or the special size() function (HQL specific feature).



select cat from Cat cat where cat.kittens.size > 0



select cat from Cat cat where size(cat.kittens) > 0



For indexed collections, you may refer to the minimum and maximum indices using minindex and maxindexfunctions. Similarly, you may refer to the minimum and maximum elements of a collection of basic type using the minelement and maxelement functions. These are HQL specific features.



select cal from Calendar cal where maxelement(cal.holidays) > current date



select order from Order order where maxindex(order.items) > 100



select order from Order order where minelement(order.items) > 10000



The SQL functions any, some, all, exists, in are supported when passed the element or index set of a collection (elements and indices functions) or the result of a subquery (see below). While subqueries are supported by JP-QL, elements and indices are specific HQL features.



select mother from Cat as mother, Cat as kit where kit in elements(foo.kittens)



select p from NameList list, Person p where p.name = some elements(list.names)



select cat from Cat cat where exists elements(cat.kittens)



select cat from Player p where 3 > all elements(p.scores)



select cat from Show show where 'fizard' in indices(show.acts)



Note that these constructs - size, elements, indices, minindex, maxindex, minelement, maxelement - may only be used in the where clause in Hibernate.

JP-QL lets you access the key or the value of a map by using the KEY() and VALUE() operations (even access the Entry object using ENTRY())



SELECT i.name, VALUE(p) FROM Item i JOIN i.photos p WHERE KEY(p) LIKE ‘%egret’



In HQL, elements of indexed collections (arrays, lists, maps) may be referred to by index (in a where clause only):



select order from Order order where order.items[0].id = 1234



select person from Person person, Calendar calendar where calendar.holidays['national day'] = person.birthDay and person.nationality.calendar = calendar



select item from Item item, Order order where order.items[ order.deliveredItemIndices[0] ] = item and order.id = 11



select item from Item item, Order order where order.items[ maxindex(order.items) ] = item and order.id = 11



The expression inside [] may even be an arithmetic expression.



select item from Item item, Order order where order.items[ size(order.items) - 1 ] = item



HQL also provides the built-in index() function, for elements of a one-to-many association or collection of values.



select item, index(item) from Order order join order.items item where index(item) < 5



Scalar SQL functions supported by the underlying database may be used



select cat from DomesticCat cat where upper(cat.name) like 'FRI%'



If you are not yet convinced by all this, think how much longer and less readable the following query would be in SQL:



select cust from Product prod, Store store inner join store.customers cust where prod.name = 'widget' and store.location.name in ( 'Melbourne', 'Sydney' ) and prod = all elements(cust.currentOrder.lineItems)



Hint:



SELECT cust.name, cust.address, cust.phone, cust.id, cust.current_order FROM customers cust, stores store, locations loc, store_customers sc, product prod WHERE prod.name = 'widget' AND store.loc_id = loc.id AND loc.name IN ( 'Melbourne', 'Sydney' ) AND sc.store_id = store.id AND sc.cust_id = cust.id AND prod.id = ALL( SELECT item.prod_id FROM line_items item, orders o WHERE item.order_id = o.id AND cust.current_order = o.id )



8.9. The order by clause



The list returned by a query may be ordered by any property of a returned class or components:



select cat from DomesticCat cat order by cat.name asc, cat.weight desc, cat.birthdate



The optional asc or desc indicate ascending or descending order respectively.



8.10. The group by clause



A query that returns aggregate values may be grouped by any property of a returned class or components:



select cat.color, sum(cat.weight), count(cat) from Cat cat group by cat.color



select foo.id, avg(name), max(name) from Foo foo join foo.names name group by foo.id



A having clause is also allowed.



select cat.color, sum(cat.weight), count(cat) from Cat cat group by cat.color having cat.color in (eg.Color.TABBY, eg.Color.BLACK)



SQL functions and aggregate functions are allowed in the having and order by clauses, if supported by the underlying database (eg. not in MySQL).



select cat from Cat cat join cat.kittens kitten group by cat having avg(kitten.weight) > 100 order by count(kitten) asc, sum(kitten.weight) desc



Note that neither the group by clause nor the order by clause may contain arithmetic expressions.



8.11. Subqueries



For databases that support subselects, JP-QL supports subqueries within queries. A subquery must be surrounded by parentheses (often by an SQL aggregate function call). Even correlated subqueries (subqueries that refer to an alias in the outer query) are allowed.



select fatcat from Cat as fatcat where fatcat.weight > ( select avg(cat.weight) from DomesticCat cat )



select cat from DomesticCat as cat where cat.name = some ( select name.nickName from Name as name )



select cat from Cat as cat where not exists ( from Cat as mate where mate.mate = cat )



select cat from DomesticCat as cat where cat.name not in ( select name.nickName from Name as name )



For subqueries with more than one expression in the select list, you can use a tuple constructor:



select cat from Cat as cat where not ( cat.name, cat.color ) in ( select cat.name, cat.color from DomesticCat cat )



Note that on some databases (but not Oracle or HSQLDB), you can use tuple constructors in other contexts, for example when querying components or composite user types:



select cat from Person where name = ('Gavin', 'A', 'King')



Which is equivalent to the more verbose:



select cat from Person where name.first = 'Gavin' and name.initial = 'A' and name.last = 'King')



There are two good reasons you might not want to do this kind of thing: first, it is not completely portable between database platforms; second, the query is now dependent upon the ordering of properties in the mapping document.



8.12. JP-QL examples



Hibernate queries can be quite powerful and complex. In fact, the power of the query language is one of Hibernate's main selling points (and now JP-QL). Here are some example queries very similar to queries that I used on a recent project. Note that most queries you will write are much simpler than these!

The following query returns the order id, number of items and total value of the order for all unpaid orders for a particular customer and given minimum total value, ordering the results by total value. In determining the prices, it uses the current catalog. The resulting SQL query, against the ORDER,ORDER_LINE, PRODUCT, CATALOG and PRICE tables has four inner joins and an (uncorrelated) subselect.



select order.id, sum(price.amount), count(item) from Order as order join order.lineItems as item join item.product as product, Catalog as catalog join catalog.prices as price where order.paid = false and order.customer = :customer and price.product = product and catalog.effectiveDate < sysdate and catalog.effectiveDate >= all ( select cat.effectiveDate from Catalog as cat where cat.effectiveDate < sysdate ) group by order having sum(price.amount) > :minAmount order by sum(price.amount) desc



What a monster! Actually, in real life, I'm not very keen on subqueries, so my query was really more like this:



select order.id, sum(price.amount), count(item) from Order as order join order.lineItems as item join item.product as product, Catalog as catalog join catalog.prices as price where order.paid = false and order.customer = :customer and price.product = product and catalog = :currentCatalog group by order having sum(price.amount) > :minAmount order by sum(price.amount) desc



The next query counts the number of payments in each status, excluding all payments in theAWAITING_APPROVAL status where the most recent status change was made by the current user. It translates to an SQL query with two inner joins and a correlated subselect against the PAYMENT,PAYMENT_STATUS and PAYMENT_STATUS_CHANGE tables.



select count(payment), status.name from Payment as payment join payment.currentStatus as status join payment.statusChanges as statusChange where payment.status.name <> PaymentStatus.AWAITING_APPROVAL or ( statusChange.timeStamp = ( select max(change.timeStamp) from PaymentStatusChange change where change.payment = payment ) and statusChange.user <> :currentUser ) group by status.name, status.sortOrder order by status.sortOrder



If I would have mapped the statusChanges collection as a list, instead of a set, the query would have been much simpler to write.



select count(payment), status.name from Payment as payment join payment.currentStatus as status where payment.status.name <> PaymentStatus.AWAITING_APPROVAL or payment.statusChanges[ maxIndex(payment.statusChanges) ].user <> :currentUser group by status.name, status.sortOrder order by status.sortOrder



However the query would have been HQL specific.

The next query uses the MS SQL Server isNull() function to return all the accounts and unpaid payments for the organization to which the current user belongs. It translates to an SQL query with three inner joins, an outer join and a subselect against the ACCOUNT, PAYMENT, PAYMENT_STATUS, ACCOUNT_TYPE,ORGANIZATION and ORG_USER tables.



select account, payment from Account as account join account.holder.users as user left outer join account.payments as payment where :currentUser = user and PaymentStatus.UNPAID = isNull(payment.currentStatus.name, PaymentStatus.UNPAID) order by account.type.sortOrder, account.accountNumber, payment.dueDate



8.13. Bulk UPDATE & DELETE Statements



Hibernate now supports UPDATE and DELETE statements in HQL/JP-QL. See Section 7.1, “Bulk update/delete” for details.



8.14. Tips & Tricks



To order a result by the size of a collection, use the following query:



select usr.id, usr.name from User as usr left join usr.messages as msg group by usr.id, usr.name order by count(msg)



If your database supports subselects, you can place a condition upon selection size in the where clause of your query:



from User usr where size(usr.messages) >= 1



If your database doesn't support subselects, use the following query:



select usr.id, usr.name from User usr.name join usr.messages msg group by usr.id, usr.name having count(msg) >= 1



As this solution can't return a User with zero messages because of the inner join, the following form is also useful:



select usr.id, usr.name from User as usr left join usr.messages as msg group by usr.id, usr.name having count(msg) = 0