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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.
For a type-safe approach to query, we highly recommend you to use the Criteria query, see Chapter 9, Criteria Queries.
Queries are case-insensitive, except for names of Java classes and
properties. So SeLeCT is the same as
sELEct is the same as SELECT but
org.hibernate.eg.FOO is not
org.hibernate.eg.Foo and foo.barSet
is not foo.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.
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).
You may also assign aliases to associated entities, or even to
elements of a collection of values, using a
join.
select cat, mate, kitten from Cat as cat
inner join cat.mate as mate
left outer join cat.kittens as kittenselect 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 kittenIn 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.kittensA 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.kittensNote that the fetch construct may not be used in
queries called using scroll() or
iterate(). Nor should fetch be 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%'
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 mateThe 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 offspror 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 offspror 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 offsprassuming 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.
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.weightselect 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
A query like:
select cat from Cat as cat
returns instances not only of Cat, but also of
subclasses like DomesticCat. Hibernate queries may name
any 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 by
clause does not correctly order the whole result set. (It also means you
can't call these queries using Query.scroll().)
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 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
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 = 123456select account from bank.Account account
where account.owner.id.country = 'AU'
and account.owner.id.medicareNumber = 123456Once 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 component address
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.
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 maxindex
functions. 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 = calendarselect 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) < 5Scalar 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: something like
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
)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.
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) descNote that neither the group by clause nor the
order by clause may contain arithmetic
expressions.
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.
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) descWhat 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) descThe next query counts the number of payments in each status,
excluding all payments in the AWAITING_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.sortOrderIf 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.sortOrderHowever 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.dueDateHibernate now supports UPDATE and DELETE statements in HQL/JP-QL. See Section 7.1, “Bulk update/delete” for details.
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) >= 1As 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) = 0Copyright © 2005 Red Hat Inc. and the various authors