Chapter 14. HQL: The Hibernate Query Language - Hibernate reference 3.2.4 sp1 版英文参考手册

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 HQL keywords. Some users find queries with uppercase keywords more readable, but we find this convention ugly when embedded in Java code.

The simplest possible Hibernate query is of the form:

from eg.Cat

which simply returns all instances of the class eg.Cat. We don't usually need to qualify the class name, since auto-import is the default. So we almost always just write:

from Cat

Most of the time, you will need to assign an alias, since you will want to refer to the Cat in other parts of the query.

from Cat as cat

This query assigns the alias cat to Cat instances, so we could use that alias later in the query. The as keyword is optional; we could also write:

from Cat cat

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

from Formula, Parameter

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).

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

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

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

from Formula form full join form.parameter param

The supported join types are borrowed from ANSI SQL

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

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

You may supply extra join conditions using the HQL with keyword.

from Cat as cat 
    left join cat.kittens as kitten 
        with kitten.bodyWeight > 10.0

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 outer join and lazy declarations of the mapping file for associations and collections. See Section 19.1, “Fetching strategies” for more information.

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:

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 iterate() (though scroll() can be used). Nor should fetch be used together with setMaxResults() or setFirstResult() as these operations are based on the result rows, which usually contain duplicates for eager collection fetching, hence, the number of rows is not what you'd expect. Nor may fetch be used together with an ad hoc with condition. It is possible to create a cartesian product by join fetching more than one collection in a query, so take care in this case. Join fetching multiple collection roles also sometimes gives unexpected results for bag mappings, so be careful about how you formulate your queries in this case. Finally, note that full join fetch and right join fetch are not meaningful.

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.

from Document fetch all properties order by name

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

HQL supports two forms of association joining: implicit and explicit.

The queries shown in the previous section all use the explicit form where the join keyword is explicitly used in the from clause. This is the recommended form.

The implicit form does not use the join keyword. Instead, the associations are "dereferenced" using dot-notation. implicit joins can appear in any of the HQL clauses. implicit join result in inner joins in the resulting SQL statement.

from Cat as cat where cat.mate.name like '%s%'

There are, generally speaking, 2 ways to refer to an entity's identifier property:

References to composite identifier properties follow the same naming rules. If the entity has a non-identifier property named id, the composite identifier property can only be referenced by its defined named; otherwise, the special id property can be used to rerference the identifier property.

Note: this has changed significantly starting in version 3.2.2. In previous versions, id always referred to the identifier property no matter what its actual name. A ramification of that decision was that non-identifier properties named id could never be referenced in Hibernate queries.

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,

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 typesafe Java 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:

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

You may use arithmetic operators, concatenation, and recognized SQL functions in the select clause:

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

A query like:

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. 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

The interface Named might be implemented by various persistent classes:

from Named n, Named m where n.name = m.name

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:

from Cat where name='Fritz'

If there is an alias, use a qualified property name:

from Cat as 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:

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

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:

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. See Section 14.5, “Refering to identifier property” for more information.

from Cat as cat where cat.id = 123

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. Again, see Section 14.5, “Refering to identifier property” for more information regarding referencing identifier properties.

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

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.

from Cat cat where cat.class = DomesticCat

You may also use components or composite user types, or properties of said component types. See ??? for more details.

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>).

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:

in and between may be used as follows:

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

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

and the negated forms may be written

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

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:

<property name="hibernate.query.substitutions">true 1, false 0</property>

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

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.

from Cat cat where cat.kittens.size > 0

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.

from Calendar cal where maxelement(cal.holidays) > current_date

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

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).

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)

from Cat cat where exists elements(cat.kittens)

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

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 Hibernate3.

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

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

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:

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.id, cat.name, cat.other, cat.properties
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. Also note that Hibernate currently does not expand a grouped entity, so you can't write group by cat if all properties of cat are non-aggregated. You have to list all non-aggregated properties explicitly.

For databases that support subselects, Hibernate 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.

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

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

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

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

select cat.id, (select max(kit.weight) from cat.kitten kit) 
from Cat as cat

Note that HQL subqueries may occur only in the select or where clauses.

Note that subqueries can also utilize row value constructor syntax. See Section 14.18, “Row value constructor syntax” for more details.

Hibernate queries can be quite powerful and complex. In fact, the power of the query language is one of Hibernate's main selling points. 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 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.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

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

For some databases, we would need to do away with the (correlated) subselect.

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

HQL now supports update, delete and insert ... select ... statements. See Section 13.4, “DML-style operations” for details.

You can count the number of query results without actually returning them:

( (Integer) session.iterate("select count(*) from ....").next() ).intValue()

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

Properties of a JavaBean can be bound to named query parameters:

Query q = s.createQuery("from foo Foo as foo where foo.name=:name and foo.size=:size");
q.setProperties(fooBean); // fooBean has getName() and getSize()
List foos = q.list();

Collections are pageable by using the Query interface with a filter:

Query q = s.createFilter( collection, "" ); // the trivial filter
q.setMaxResults(PAGE_SIZE);
q.setFirstResult(PAGE_SIZE * pageNumber);
List page = q.list();

Collection elements may be ordered or grouped using a query filter:

Collection orderedCollection = s.filter( collection, "order by this.amount" );
Collection counts = s.filter( collection, "select this.type, count(this) group by this.type" );

You can find the size of a collection without initializing it:

( (Integer) session.iterate("select count(*) from ....").next() ).intValue();

Components might be used in just about every way that simple value types can be used in HQL queries. They can appear in the select clause:

select p.name from from Person p

select p.name.first from from Person p

where the Person's name property is a component. Components can also be used in the where clause:

from from Person p where p.name = :name

from from Person p where p.name.first = :firstName

Components can also be used in the order by clause:

from from Person p order by p.name

from from Person p order by p.name.first

Another common use of components is in Section 14.18, “Row value constructor syntax”.

HQL supports the use of ANSI SQL row value constructor syntax (sometimes called tuple syntax), even though the underlying database may not support that notion. Here we are generally referring to multi-valued comparisons, typically associated with components. Consider an entity Person which defines a name component:

from Person p where p.name.first='John' and p.name.last='Jingleheimer-Schmidt'

That's valid syntax, although a little verbose. It be nice to make this a bit more concise and use row value constructor syntax:

from Person p where p.name=('John', 'Jingleheimer-Schmidt')

It can also be useful to specify this in the select clause:

select p.name from from Person p

Another time using row value constructor syntax can be beneficial is when using subqueries needing to compare against multiple values:

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

One thing to consider when deciding if you want to use this syntax is that the query will be dependent upon the ordering of the component sub-properties in the metadata.