The Hibernate Query Language (HQL) and Java Persistence Query Language (JPQL) are both object model focused query languages similar in nature to SQL. JPQL is a heavily-inspired-by subset of HQL. A JPQL query is always a valid HQL query, the reverse is not true, however.
Both HQL and JPQL are non-type-safe ways to perform query operations. Criteria queries offer a type-safe approach to querying. See Criteria for more information.
To better understand the further HQL and JPQL examples, it’s time to familiarize the domain model entities that are used in all the examples features in this chapter.
link:../../../../../../main/java/org/hibernate/userguide/model/Person.java[role=include]
link:../../../../../../main/java/org/hibernate/userguide/model/AddressType.java[role=include]
link:../../../../../../main/java/org/hibernate/userguide/model/Partner.java[role=include]
link:../../../../../../main/java/org/hibernate/userguide/model/Phone.java[role=include]
link:../../../../../../main/java/org/hibernate/userguide/model/PhoneType.java[role=include]
link:../../../../../../main/java/org/hibernate/userguide/model/Call.java[role=include]
link:../../../../../../main/java/org/hibernate/userguide/model/Payment.java[role=include]
link:../../../../../../main/java/org/hibernate/userguide/model/CreditCardPayment.java[role=include]
link:../../../../../../main/java/org/hibernate/userguide/model/WireTransferPayment.java[role=include]
When using Hibernate, you can execute entity queries either via Jakarta Persistence or the Hibernate-specific API.
Since 5.2, the Hibernate Session
interface extends the Jakarta Persistence EntityManager
interface.
For this reason, the query API was also merged, and now the Hibernate org.hibernate.query.Query
interface extends the Jakarta Persistence jakarta.persistence.Query
.
Next, we are going to see how the query API differs between the standard Jakarta Persistence interfaces and the Hibernate-specific API.
In Jakarta Persistence, the query is represented by jakarta.persistence.Query
or jakarta.persistence.TypedQuery
as obtained from the EntityManager
.
The create an inline Query
or TypedQuery
, you need to use the EntityManager#createQuery
method.
For named queries, the EntityManager#createNamedQuery
method is needed.
Query
or a TypedQuery
referencelink:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
Query
or a TypedQuery
reference for a named querylink:../../../../../../main/java/org/hibernate/userguide/model/Person.java[role=include]
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
Hibernate offers a specific
@NamedQuery
annotation
which provides ways to configure various query features, like flush mode, cacheability, time out interval.
Query
or a TypedQuery
reference for a named querylink:../../../../../../main/java/org/hibernate/userguide/model/Phone.java[role=include]
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
The Query
interface can then be used to control the execution of the query.
For example, we may want to specify an execution timeout or control caching.
Query
usagelink:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
For complete details, see the Query
{jpaJavadocUrlPrefix}Query.html[Javadocs].
Many of the settings controlling the execution of the query are defined as hints.
Jakarta Persistence defines some standard hints (like timeout in the example), but most are provider specific.
Relying on provider specific hints limits your applications portability to some degree.
jakarta.persistence.query.timeout
-
Defines the query timeout, in milliseconds.
jakarta.persistence.fetchgraph
-
Defines a fetchgraph EntityGraph. Attributes explicitly specified as
AttributeNodes
are treated asFetchType.EAGER
(via join fetch or subsequent select). For details, see the EntityGraph discussions in Fetching. jakarta.persistence.loadgraph
-
Defines a loadgraph EntityGraph. Attributes explicitly specified as AttributeNodes are treated as
FetchType.EAGER
(via join fetch or subsequent select). Attributes that are not specified are treated asFetchType.LAZY
orFetchType.EAGER
depending on the attribute’s definition in metadata. For details, see the EntityGraph discussions in Fetching. org.hibernate.cacheMode
-
Defines the
CacheMode
to use. Seeorg.hibernate.query.Query#setCacheMode
. org.hibernate.cacheable
-
Defines whether the query is cacheable. true/false. See
org.hibernate.query.Query#setCacheable
. org.hibernate.cacheRegion
-
For queries that are cacheable, defines a specific cache region to use. See
org.hibernate.query.Query#setCacheRegion
. org.hibernate.comment
-
Defines the comment to apply to the generated SQL. See
org.hibernate.query.Query#setComment
. org.hibernate.fetchSize
-
Defines the JDBC fetch-size to use. See
org.hibernate.query.Query#setFetchSize
. org.hibernate.flushMode
-
Defines the Hibernate-specific
FlushMode
to use. Seeorg.hibernate.query.Query#setFlushMode.
If possible, prefer usingjakarta.persistence.Query#setFlushMode
instead. org.hibernate.readOnly
-
Defines that entities and collections loaded by this query should be marked as read-only. See
org.hibernate.query.Query#setReadOnly
.
The final thing that needs to happen before the query can be executed is to bind the values for any defined parameters.
Jakarta Persistence defines a simplified set of parameter binding methods.
Essentially, it supports setting the parameter value (by name/position) and a specialized form for Calendar
/Date
types additionally accepting a TemporalType
.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
JPQL-style positional parameters are declared using a question mark followed by an ordinal - ?1
, ?2
.
The ordinals start with 1.
Just like with named parameters, positional parameters can also appear multiple times in a query.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
Note
|
It’s good practice not to mix parameter binding forms in a given query. |
In terms of execution, Jakarta Persistence Query
offers 3 different methods for retrieving a result set.
-
Query#getResultList()
- executes the select query and returns back the list of results. -
Query#getResultStream()
- executes the select query and returns back aStream
over the results. -
Query#getSingleResult()
- executes the select query and returns a single result. If there were more than one result an exception is thrown.
getResultList()
resultlink:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
getResultStream()
resultlink:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
getSingleResult()
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
In Hibernate, the HQL query is represented as org.hibernate.query.Query
which is obtained from a Session
.
If the HQL is a named query, Session#getNamedQuery
would be used; otherwise Session#createQuery
is needed.
Query
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
Query
reference for a named querylink:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
Note
|
Not only was the JPQL syntax heavily inspired by HQL, but many of the Jakarta Persistence APIs were heavily inspired by Hibernate too.
The two |
The Query interface can then be used to control the execution of the query. For example, we may want to specify an execution timeout or control caching.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
For complete details, see the Query Javadocs.
Important
|
Query hints here are database query hints.
They are added directly to the generated SQL according to The Jakarta Persistence notion of query hints, on the other hand, refer to hints that target the provider (Hibernate). So even though they are called the same, be aware they have a very different purpose. Also, be aware that Hibernate query hints generally make the application non-portable across databases unless the code adding them first checks the Dialect. |
Flushing is covered in detail in Flushing. Locking is covered in detail in Locking. The concept of read-only state is covered in Persistence Contexts.
Hibernate also allows an application to hook into the process of building the query results via the org.hibernate.transform.ResultTransformer
contract.
See its Javadocs as well as the Hibernate-provided implementations for additional details.
The last thing that needs to happen before we can execute the query is to bind the values for any parameters defined in the query. Query defines many overloaded methods for this purpose. The most generic form takes the value as well as the Hibernate Type.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
Hibernate generally understands the expected type of the parameter given its context in the query.
In the previous example since we are using the parameter in a LIKE
comparison against a String-typed attribute Hibernate would automatically infer the type; so the above could be simplified.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
There are also short hand forms for binding common types such as strings, booleans, integers, etc.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
Important
|
Traditionally, Hibernate used to support a JDBC positional parameter syntax form via a There was no way to relate two such positional parameters as being "the same" aside from binding the same value to each and, for this reason, this form is no longer supported. link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include] |
In terms of execution, Hibernate offers 4 different methods. The 2 most commonly used are
-
Query#list
- executes the select query and returns back the list of results. -
Query#uniqueResult
- executes the select query and returns the single result. If there were more than one result an exception is thrown.
list()
resultlink:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
It is also possible to extract a single result from a Query
.
uniqueResult()
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
Note
|
If the unique result is used often and the attributes upon which it is based are unique, you may want to consider mapping a natural-id and using the natural-id loading API. See the Natural Ids for more information on this topic. |
Hibernate offers additional, specialized methods for scrolling the query and handling results using a server-side cursor.
Query#scroll
works in tandem with the JDBC notion of a scrollable ResultSet
.
The Query#scroll
method is overloaded:
-
The main form accepts a single argument of type
org.hibernate.ScrollMode
which indicates the type of scrolling to be used. See the Javadocs for the details on each. -
The second form takes no argument and will use the
ScrollMode
indicated byDialect#defaultScrollMode
.
Query#scroll
returns a org.hibernate.ScrollableResults
which wraps the underlying JDBC (scrollable) ResultSet
and provides access to the results.
Unlike a typical forward-only ResultSet
, the ScrollableResults
allows you to navigate the ResultSet
in any direction.
ResultSet
containing entitieslink:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
Important
|
Since this form holds the JDBC If left unclosed by the application, Hibernate will automatically close the underlying resources (e.g. However, it is good practice to close the |
Note
|
If you plan to use |
Hibernate also supports Query#iterate
, which is intended for loading entities when it is known that the loaded entries are already stored in the second-level cache.
The idea behind iterate is that just the matching identifiers will be obtained in the SQL query.
From these the identifiers are resolved by second-level cache lookup.
If these second-level cache lookups fail, additional queries will need to be issued against the database.
Note
|
This operation can perform significantly better for loading large numbers of entities that for certain already exist in the second-level cache. In cases where many of the entities do not exist in the second-level cache, this operation will almost definitely perform worse. |
The Iterator
returned from Query#iterate
is actually a specially typed Iterator: org.hibernate.engine.HibernateIterator
.
It is specialized to expose a close()
method (again, inherited from java.io.Closeable
).
When you are done with this Iterator
you should close it, either by casting to HibernateIterator
or Closeable
, or by calling Hibernate#close(java.util.Iterator)
.
Since 5.2, Hibernate offers support for returning a Stream
which can be later used to transform the underlying ResultSet
.
Internally, the stream()
behaves like a Query#scroll
and the underlying result is backed by a ScrollableResults
.
Fetching a projection using the Query#stream
method can be done as follows:
stream()
using a projection result typelink:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
When fetching a single result, like a Person
entity, instead of a Stream<Object[]>
, Hibernate is going to figure out the actual type, so the result is a Stream<Person>
.
stream()
using an entity result typelink:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
Important
|
Just like with |
The Jakarta Persistence Query
interface offers support for returning a Stream
via the getResultStream
method.
Just like the scroll
method, you can use a try-with-resources block to close the Stream
prior to closing the currently running Persistence Context.
Since Hibernate 5.4, the Stream
is also closed when calling a terminal operation,
as illustrated by the following example.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
The Stream
is closed automatically after calling the collect
method,
since there is no reason to keep the underlying JDBC ResultSet
open
if the Stream
cannot be reused.
With the exception of names of Java classes and properties, queries are case-insensitive.
So SeLeCT
is the same as sELEct
is the same as SELECT
, but org.hibernate.eg.FOO
and org.hibernate.eg.Foo
are different, as are foo.barSet
and foo.BARSET
.
Note
|
This documentation uses lowercase keywords as a convention in query examples. |
Both HQL and JPQL allow SELECT
, UPDATE
and DELETE
statements to be performed.
HQL additionally allows INSERT
statements, in a form similar to a SQL INSERT FROM SELECT
.
Important
|
Care should be taken as to when an
— Section 4.10 of the Java Persistence 2.0 Specification
|
The BNF for SELECT
statements in HQL is:
link:extras/statement_select_bnf.txt[role=include]
The simplest possible HQL SELECT
statement is of the form:
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
Note
|
The select statement in JPQL is exactly the same as for HQL except that JPQL requires a link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include] Even though HQL does not require the presence of a It is usually better to explicitly specify intent.
Hibernate does not actually enforce that a |
The BNF for UPDATE
statements is the same in HQL and JPQL:
link:extras/statement_update_bnf.txt[role=include]
UPDATE
statements, by default, do not affect the version
or the timestamp
attribute values for the affected entities.
However, you can force Hibernate to set the version
or timestamp
attribute values through the use of a versioned update
.
This is achieved by adding the VERSIONED
keyword after the UPDATE
keyword.
Note
|
Versioned updates is a Hibernate-specific feature and will not work in a portable manner. Custom version types, |
An UPDATE
statement is executed using the executeUpdate()
of either org.hibernate.query.Query
or jakarta.persistence.Query
.
The method is named for those familiar with the JDBC executeUpdate()
on java.sql.PreparedStatement
.
The int
value returned by the executeUpdate()
method indicates the number of entities affected by the operation.
This may or may not correlate to the number of rows affected in the database.
An HQL bulk operation might result in multiple actual SQL statements being executed (for joined-subclass, for example).
The returned number indicates the number of actual entities affected by the statement.
Using a JOINED inheritance hierarchy, a delete against one of the subclasses may actually result in deletes against not just the table to which that subclass is mapped, but also the "root" table and tables "in between".
link:../../../../../../test/java/org/hibernate/userguide/hql/../batch/BatchTest.java[role=include]
link:../../../../../../test/java/org/hibernate/userguide/hql/../batch/BatchTest.java[role=include]
link:../../../../../../test/java/org/hibernate/userguide/hql/../batch/BatchTest.java[role=include]
Important
|
Neither |
The BNF for DELETE
statements is the same in HQL and JPQL:
link:extras/statement_delete_bnf.txt[role=include]
A DELETE
statement is also executed using the executeUpdate()
method of either org.hibernate.query.Query
or jakarta.persistence.Query
.
HQL adds the ability to define INSERT
statements as well.
Note
|
There is no JPQL equivalent to HQL-style INSERT statements. |
The BNF for an HQL INSERT
statement is:
link:extras/statement_insert_bnf.txt[role=include]
The attribute_list
is analogous to the column specification
in the SQL INSERT
statement.
For entities involved in mapped inheritance, only attributes directly defined on the named entity can be used in the attribute_list
.
Superclass properties are not allowed and subclass properties do not make sense.
In other words, INSERT
statements are inherently non-polymorphic.
select_statement
can be any valid HQL select query, with the caveat that the return types must match the types expected by the insert.
Currently, this is checked during query compilation rather than allowing the check to delegate to the database.
This may cause problems between Hibernate Types which are equivalent as opposed to equal.
For example, this might lead to issues with mismatches between an attribute mapped as a org.hibernate.type.StandardBasicTypes.DATE
and an attribute defined as a org.hibernate.type.StandardBasicTypes.TIMESTAMP
,
even though the database might not make a distinction or might be able to handle the conversion.
For the id attribute, the insert statement gives you two options.
You can either explicitly specify the id property in the attribute_list
, in which case its value is taken from the corresponding select expression, or omit it from the attribute_list
in which case a generated value is used.
This latter option is only available when using id generators that operate "in the database"; attempting to use this option with any "in memory" type generators will cause an exception during parsing.
For optimistic locking attributes, the insert statement again gives you two options.
You can either specify the attribute in the attribute_list
in which case its value is taken from the corresponding select expressions or omit it from the attribute_list
in which case the seed value
defined by the corresponding org.hibernate.type.VersionType
is used.
link:../../../../../../test/java/org/hibernate/userguide/hql/../batch/BatchTest.java[role=include]
The FROM
clause is responsible for defining the scope of object model types available to the rest of the query.
It is also responsible for defining all the "identification variables" available to the rest of the query.
Identification variables are often referred to as aliases.
References to object model classes in the FROM
clause can be associated with an identification variable that can then be used to refer to that type throughout the rest of the query.
In most cases declaring an identification variable is optional, though it is usually good practice to declare them.
An identification variable must follow the rules for Java identifier validity.
According to JPQL, identification variables must be treated as case-insensitive. Good practice says you should use the same case throughout a query to refer to a given identification variable. In other words, JPQL says they can be case-insensitive and so Hibernate must be able to treat them as such, but this does not make it good practice.
A root entity reference, or what Jakarta Persistence calls a range variable declaration
, is specifically a reference to a mapped entity type from the application.
It cannot name component/embeddable types.
And associations, including collections, are handled in a different manner, as later discussed.
The BNF for a root entity reference is:
link:extras/root_entity_ref_bnf.txt[role=include]
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
We see that the query is defining a root entity reference to the org.hibernate.userguide.model.Person
object model type.
Additionally, it declares an alias of p
to that org.hibernate.userguide.model.Person
reference, which is the identification variable.
Usually, the root entity reference represents just the entity name
rather than the entity class FQN (fully-qualified name).
By default, the entity name is the unqualified entity class name, here Person
.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
Multiple root entity references can also be specified, even when naming the same entity.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
The FROM
clause can also contain explicit relationship joins using the join
keyword.
These joins can be either inner
or left outer
style joins.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
HQL also defines a WITH
clause to qualify the join conditions.
Note
|
The HQL-style WITH keyword is specific to Hibernate. JPQL defines the |
WITH
clause join examplelink:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
ON
clause join examplelink:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
Note
|
The important distinction is that in the generated SQL the conditions of the |
The distinction in this specific example is probably not that significant.
The with clause
is sometimes necessary for more complicated queries.
Explicit joins may reference association or component/embedded attributes. In the case of component/embedded attributes, the join is simply logical and does not correlate to a physical (SQL) join. For further information about collection-valued association references, see Collection member references.
An important use case for explicit joins is to define FETCH JOIN
s which override the laziness of the joined association.
As an example, given an entity named Person
with a collection-valued association named phones
, the JOIN FETCH
will also load the child collection in the same SQL query:
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
As you can see from the example, a fetch join is specified by injecting the keyword fetch
after the keyword join
.
In the example, we used a left outer join because we also wanted to return customers who have no orders.
Inner joins can also be fetched, but inner joins filter out the root entity. In the example, using an inner join instead would have resulted in customers without any orders being filtered out of the result.
Important
|
Fetch joins are not valid in sub-queries. Care should be taken when fetch joining a collection-valued association which is in any way further restricted (the fetched collection will be restricted too). For this reason, it is usually considered best practice not to assign an identification variable to fetched joins except for the purpose of specifying nested fetch joins. Fetch joins should not be used in paged queries (e.g. |
Another means of adding to the scope of object model types available to the query is through the use of implicit joins or path expressions.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
An implicit join always starts from an identification variable
, followed by the navigation operator ( .
),
followed by an attribute for the object model type referenced by the initial identification variable
.
In the example, the initial identification variable
is ph
which refers to the Phone
entity.
The ph.person
reference then refers to the person
attribute of the Phone
entity.
person
is an association type so we further navigate to its age attribute.
Important
|
If the attribute represents an entity association (non-collection) or a component/embedded, that reference can be further navigated. Basic values and collection-valued associations cannot be further navigated. |
As shown in the example, implicit joins can appear outside the FROM clause
.
However, they affect the FROM clause
.
Note
|
Implicit joins are always treated as inner joins. Multiple references to the same implicit join always refer to the same logical and physical (SQL) join. |
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
Just as with explicit joins, implicit joins may reference association or component/embedded attributes. For further information about collection-valued association references, see Collection member references.
In the case of component/embedded attributes, the join is simply logical and does not correlate to a physical (SQL) join. Unlike explicit joins, however, implicit joins may also reference basic state fields as long as the path expression ends there.
For JPQL and HQL, DISTINCT
has two meanings:
-
It can be passed to the database so that duplicates are removed from a result set
-
It can be used to filter out the same parent entity references when join fetching a child collection
For SQL projections, DISTINCT
needs to be passed to the database because the duplicated entries need to be filtered out before being returned to the database client.
link:../../../../../../test/java/org/hibernate/userguide/hql/SelectDistinctTest.java[role=include]
When running the query above, Hibernate generates the following SQL query:
link:extras/hql-distinct-projection-query-example.sql[role=include]
For this particular use case, passing the DISTINCT
keyword from JPQL/HQL to the database is the right thing to do.
DISTINCT
can also be used to filter out entity object references when fetching a child association along with the parent entities.
link:../../../../../../test/java/org/hibernate/userguide/hql/SelectDistinctTest.java[role=include]
In this case, DISTINCT
is used because there can be multiple Books
entities associated with a given Person
.
If in the database there are 3 Person
s in the database and each person has 2 Book
s, without DISTINCT
this query will return 6 Person
s since
the SQL-level result-set size is given by the number of joined Book
records.
However, the DISTINCT
keyword is passed to the database as well:
link:extras/hql-distinct-entity-query-example.sql[role=include]
In this case, the DISTINCT
SQL keyword is undesirable since it does a redundant result set sorting, as explained in this blog post.
To fix this issue, Hibernate 5.2.2 added support for the HINT_PASS_DISTINCT_THROUGH
entity query hint:
link:../../../../../../test/java/org/hibernate/userguide/hql/SelectDistinctTest.java[role=include]
With this entity query hint, Hibernate will not pass the DISTINCT
keyword to the SQL query:
link:extras/hql-distinct-entity-query-hint-example.sql[role=include]
When using the HINT_PASS_DISTINCT_THROUGH
entity query hint, Hibernate can still remove the duplicated parent-side entities from the query result.
References to collection-valued associations actually refer to the values of that collection.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
In the example, the identification variable ph
actually refers to the object model type Phone
, which is the type of the elements of the Person#phones
association.
The example also shows the alternate syntax for specifying collection association joins using the IN
syntax.
Both forms are equivalent.
Which form an application chooses to use is simply a matter of taste.
We said earlier that collection-valued associations actually refer to the values of that collection. Based on the type of collection, there are also a set of explicit qualification expressions available.
link:../../../../../../main/java/org/hibernate/userguide/model/Phone.java[role=include]
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
- VALUE
-
Refers to the collection value. Same as not specifying a qualifier. Useful to explicitly show intent. Valid for any type of collection-valued reference.
- INDEX
-
According to HQL rules, this is valid for both
Maps
andLists
which specify ajakarta.persistence.OrderColumn
annotation to refer to theMap
key or theList
position (aka theOrderColumn
value). JPQL however, reserves this for use in theList
case and addsKEY
for theMap
case. Applications interested in Jakarta Persistence provider portability should be aware of this distinction. - KEY
-
Valid only for
Maps
. Refers to the map’s key. If the key is itself an entity, it can be further navigated. - ENTRY
-
Only valid for
Maps
. Refers to the map’s logicaljava.util.Map.Entry
tuple (the combination of its key and value).ENTRY
is only valid as a terminal path and it’s applicable to theSELECT
clause only.
See Collection-related expressions for additional details on collection-related expressions.
HQL and JPQL queries are inherently polymorphic.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
This query names the Payment
entity explicitly.
However, all subclasses of Payment
are also available to the query.
So, if the CreditCardPayment
and WireTransferPayment
entities extend the Payment
class, all three types would be available to the entity query,
and the query would return instances of all three.
This behavior can be altered in two ways:
-
by limiting the query to select only from the subclass entity.
-
by using either the
org.hibernate.annotations.Polymorphism
annotation (global, and Hibernate-specific). See the@Polymorphism
section for more info about this use case.
Note
|
The HQL query It returns every object of every entity type defined by your application mappings. |
See The FROM
clause.
Again, see The FROM
clause.
String literals are enclosed in single quotes. To escape a single quote within a string literal, use double single quotes.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
Numeric literals are allowed in a few different forms.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
Note
|
In the scientific notation form, the Specific typing can be achieved through the use of the same suffix approach specified by Java.
So, The boolean literals are Enums can even be referenced as literals. The fully-qualified enum class name must be used. HQL can also handle constants in the same manner, though JPQL does not define that as being supported. Entity names can also be used as literal. See Entity type. Date/time literals can be specified using the JDBC escape syntax:
These Date/time literals only work if the underlying JDBC driver supports them. |
Arithmetic operations also represent valid expressions.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
The following rules apply to the result of arithmetic operations:
-
If either of the operands is
Double
/double
, the result is aDouble
-
else, if either of the operands is
Float
/float
, the result is aFloat
-
else, if either operand is
BigDecimal
, the result isBigDecimal
-
else, if either operand is
BigInteger
, the result isBigInteger
(except for division, in which case the result type is not further defined) -
else, if either operand is
Long
/long
, the result isLong
(except for division, in which case the result type is not further defined) -
else, (the assumption being that both operands are of integral type) the result is
Integer
(except for division, in which case the result type is not further defined)
Date arithmetic is also supported, albeit in a more limited fashion.
This is due to differences in database support and partly to the lack of support for INTERVAL
definition in the query language itself.
HQL defines a concatenation operator in addition to supporting the concatenation (CONCAT
) function.
This is not defined by JPQL, so portable applications should avoid its use.
The concatenation operator is taken from the SQL concatenation operator (e.g ||
).
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
See Scalar functions for details on the concat()
function.
Aggregate functions are also valid expressions in HQL and JPQL. The semantics is the same as their SQL counterpart. The supported aggregate functions are:
COUNT
(including distinct/all qualifiers)-
The result type is always
Long
. AVG
-
The result type is always
Double
. MIN
-
The result type is the same as the argument type.
MAX
-
The result type is the same as the argument type.
SUM
-
The result type of the
SUM()
function depends on the type of the values being summed. For integral values (other thanBigInteger
), the result type isLong
.
For floating point values (other than BigDecimal
) the result type is Double
.
For BigInteger
values, the result type is BigInteger
. For BigDecimal
values, the result type is BigDecimal
.
Aggregations often appear with grouping. For information on grouping see Group by.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
All of these aggregate functions also support the inclusion of a specific filter clause
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
Both HQL and JPQL define some standard functions that are available regardless of the underlying database in use. HQL can also understand additional functions defined by the Dialect as well as the application.
Here is the list of functions defined as supported by JPQL. Applications interested in remaining portable between Jakarta Persistence providers should stick to these functions.
- CONCAT
-
String concatenation function. Variable argument length of 2 or more string values to be concatenated together.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
- SUBSTRING
-
Extracts a portion of a string value. The second argument denotes the starting position, where 1 is the first character of the string. The third (optional) argument denotes the length.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
- UPPER
-
Upper cases the specified string.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
- LOWER
-
Lower cases the specified string.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
- TRIM
-
Follows the semantics of the SQL trim function.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
- LENGTH
-
Returns the length of a string.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
- LOCATE
-
Locates a string within another string. The third argument (optional) is used to denote a position from which to start looking.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
- ABS
-
Calculates the mathematical absolute value of a numeric value.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
- MOD
-
Calculates the remainder of dividing the first argument by the second.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
- SQRT
-
Calculates the mathematical square root of a numeric value.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
- CURRENT_DATE
-
Returns the database current date.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
- CURRENT_TIME
-
Returns the database current time.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
- CURRENT_TIMESTAMP
-
Returns the database current timestamp.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
Beyond the JPQL standardized functions, HQL makes some additional functions available regardless of the underlying database in use.
- BIT_LENGTH
-
Returns the length of binary data.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
- CAST
-
Performs a SQL cast. The cast target should name the Hibernate mapping type to use. See the data types chapter on for more information.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
- EXTRACT
-
Performs a SQL extraction on datetime values. An extraction extracts parts of the datetime (the year, for example).
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
See the abbreviated forms below.
- YEAR
-
Abbreviated extract form for extracting the year.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
- MONTH
-
Abbreviated extract form for extracting the month.
- DAY
-
Abbreviated extract form for extracting the day.
- HOUR
-
Abbreviated extract form for extracting the hour.
- MINUTE
-
Abbreviated extract form for extracting the minute.
- SECOND
-
Abbreviated extract form for extracting the second.
- STR
-
Abbreviated form for casting a value as character data.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
Hibernate Dialects can register additional functions known to be available for that particular database product. These functions are also available in HQL (and JPQL, though only when using Hibernate as the Jakarta Persistence provider, obviously). However, they would only be available when using that database Dialect. Applications that aim for database portability should avoid using functions in this category.
Application developers can also supply their own set of functions.
This would usually represent either user-defined SQL functions or aliases for snippets of SQL.
Such function declarations are made by using the addSqlFunction()
method of
the org.hibernate.boot.MetadataBuilder
or the legacy org.hibernate.cfg.Configuration
.
Now, let’s assume we have the following apply_vat
PostgreSQL user-defined function:
link:../../../../../../test/java/org/hibernate/userguide/hql/PostgreSQLFunctionWhereClauseTest.java[role=include]
Let’s consider we have persisted the following entity in our database:
link:../../../../../../test/java/org/hibernate/userguide/hql/PostgreSQLFunctionWhereClauseTest.java[role=include]
By default, Hibernate can pass through any user-defined function that’s being used in the WHERE clause of a JPQL/HQL entity query.
link:../../../../../../test/java/org/hibernate/userguide/hql/PostgreSQLFunctionWhereClauseTest.java[role=include]
While this works just fine with Hibernate, it might be a problem with other Jakarta Persistence providers.
For this purpose, Jakarta Persistence offers the function
JPQL keyword which works as follows.
function
keywordlink:../../../../../../test/java/org/hibernate/userguide/hql/PostgreSQLFunctionWhereClauseTest.java[role=include]
When the user-defined function is referenced in the SELECT clause of a JPQL/HQL entity query, Hibernate can no longer pass it through unless the function is registered.
MetadataBuilderContributor
link:../../../../../../test/java/org/hibernate/userguide/hql/PostgreSQLFunctionSelectClauseTest.java[role=include]
Now that that apply_vat
is registered, we can reference it in the JPQL SELECT clause.
link:../../../../../../test/java/org/hibernate/userguide/hql/PostgreSQLFunctionSelectClauseTest.java[role=include]
There are a few specialized expressions for working with collection-valued associations. Generally, these are just abbreviated forms or other expressions for the sake of conciseness.
- SIZE
-
Calculate the size of a collection. Equates to a subquery!
- MAXELEMENT
-
Available for use on collections of basic type. Refers to the maximum value as determined by applying the
max
SQL aggregation. - MAXINDEX
-
Available for use on indexed collections. Refers to the maximum index (key/position) as determined by applying the
max
SQL aggregation. - MINELEMENT
-
Available for use on collections of basic type. Refers to the minimum value as determined by applying the
min
SQL aggregation. - MININDEX
-
Available for use on indexed collections. Refers to the minimum index (key/position) as determined by applying the
min
SQL aggregation. - ELEMENTS
-
Used to refer to the elements of a collection as a whole. Only allowed in the where clause. Often used in conjunction with
ALL
,ANY
orSOME
restrictions. - INDICES
-
Similar to
elements
except that theindices
expression refers to the collections indices (keys/positions) as a whole.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
Elements of indexed collections (arrays, lists, and maps) can be referred to by index operator.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
See also Special case - qualified path expressions as there is a good deal of overlap.
We can also refer to the type of an entity as an expression.
This is mainly useful when dealing with entity inheritance hierarchies.
The type can be expressed using a TYPE
function used to refer to the type of an identification variable representing an entity.
The name of the entity also serves as a way to refer to an entity type.
Additionally, the entity type can be parameterized, in which case the entity’s Java Class reference would be bound as the parameter value.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
Note
|
HQL also has a legacy form of referring to an entity type using the The legacy form would have used |
Both the simple and searched forms are supported, as well as the two SQL defined abbreviated forms (NULLIF
and COALESCE
)
The simple form has the following syntax:
link:extras/simple_case_bnf.txt[role=include]
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
The searched form has the following syntax:
link:extras/searched_case_bnf.txt[role=include]
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
If you want to use arithmetic operations in the CASE expressions, you need to wrap the arithmetic operation in parentheses as illustrated by the following example:
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
Important
|
Without wrapping the arithmetic expression in |
NULLIF is an abbreviated CASE expression that returns NULL if its operands are considered equal.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
COALESCE
is an abbreviated CASE expression that returns the first non-null operand.
We have seen a number of COALESCE
examples above.
The SELECT
clause identifies which objects and values to return as the query results.
The expressions discussed in Expressions are all valid select expressions, except where otherwise noted.
See the section Hibernate Query API for information on handling the results depending on the types of values specified in the SELECT
clause.
There is a particular expression type that is only valid in the select clause. Hibernate calls this "dynamic instantiation". JPQL supports some of that feature and calls it a "constructor expression".
So rather than dealing with the Object[]
(again, see Hibernate Query API) here, we are wrapping the values in a type-safe Java object that will be returned as the results of the query.
link:../../../../../../test/java/org/hibernate/userguide/hql/CallStatistics.java[role=include]
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
Note
|
The projection class must be fully qualified in the entity query, and it must define a matching constructor. |
Important
|
The class here need not be mapped. It can be a DTO class. If it does represent an entity, the resulting instances are returned in the NEW state (not managed!). |
HQL supports additional "dynamic instantiation" features.
First, the query can specify to return a List
rather than an Object[]
for scalar results:
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
The results from this query will be a List<List>
as opposed to a List<Object[]>
HQL also supports wrapping the scalar results in a Map
.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
The results from this query will be a List<Map<String, Object>>
as opposed to a List<Object[]>
.
The keys of the map are defined by the aliases given to the select expressions.
If the user doesn’t assign aliases, the key will be the index of each particular result set column (e.g. 0, 1, 2, etc).
Predicates form the basis of the where clause, the having clause and searched case expressions.
They are expressions which resolve to a truth value, generally TRUE
or FALSE
, although boolean comparisons involving NULL
resolve typically to UNKNOWN
.
Comparisons involve one of the comparison operators: =
, >
, >=
, <
, <=
, <>
.
HQL also defines !=
as a comparison operator synonymous with <>
.
The operands should be of the same type.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
Comparisons can also involve subquery qualifiers: ALL
, ANY
, SOME
. SOME
and ANY
are synonymous.
The ALL
qualifier resolves to true if the comparison is true for all of the values in the result of the subquery.
It resolves to false if the subquery result is empty.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
The ANY
/SOME
qualifier resolves to true if the comparison is true for some of (at least one of) the values in the result of the subquery.
It resolves to false if the subquery result is empty.
It check a value for nullness. It can be applied to basic attribute references, entity references, and parameters. HQL additionally allows it to be applied to component/embeddable types.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
Performs a like comparison on string values. The syntax is:
link:extras/predicate_like_bnf.txt[role=include]
The semantics follow that of the SQL like expression.
The pattern_value
is the pattern to attempt to match in the string_expression
.
Just like SQL, pattern_value
can use _
and %
as wildcards.
The meanings are the same. The _
symbol matches any single character and %
matches any number of characters.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
The optional escape 'escape character'
is used to specify an escape character used to escape the special meaning of _
and %
in the pattern_value
.
This is useful when needing to search on patterns including either _
or %
.
The syntax is formed as follows: 'like_predicate' escape 'escape_symbol'
So, if |
is the escape symbol and we want to match all stored procedures prefixed with Dr_
, the like criteria becomes: 'Dr|_%' escape '|'
:
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
Performs a case-insensitive like comparison on string values. The syntax is:
link:extras/predicate_ilike_bnf.txt[role=include]
The semantics are identical to those of the aforementioned Like predicate, with the sole difference that the comparison is now case insensitive.
Analogous to the SQL BETWEEN
expression,
it checks if the value is within boundaries.
All the operands should have comparable types.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
IN
predicates performs a check that a particular value is in a list of values. Its syntax is:
link:extras/predicate_in_bnf.txt[role=include]
The types of the single_valued_expression
and the individual values in the single_valued_list
must be consistent.
JPQL limits the valid types here to string, numeric, date, time, timestamp, and enum types, and, in JPQL, single_valued_expression
can only refer to:
-
"state fields", which is its term for simple attributes. Specifically, this excludes association and component/embedded attributes.
-
entity type expressions. See Entity type.
In HQL, single_valued_expression
can refer to a far more broad set of expression types.
Single-valued association are allowed, and so are component/embedded attributes, although that feature depends on the level of support for tuple or "row value constructor syntax" in the underlying database.
Additionally, HQL does not limit the value type in any way, though application developers should be aware that different types may incur limited support based on the underlying database vendor.
This is largely the reason for the JPQL limitations.
The list of values can come from a number of different sources.
In the constructor_expression
and collection_valued_input_parameter
, the list of values must not be empty; it must contain at least one value.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
Exists expressions test the existence of results from a subquery. The affirmative form returns true if the subquery result contains values. The negated form returns true if the subquery result is empty.
The IS [NOT] EMPTY
expression applies to collection-valued path expressions.
It checks whether the particular collection has any associated values.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
The [NOT] MEMBER [OF]
expression applies to collection-valued path expressions.
It checks whether a value is a member of the specified collection.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
The NOT
operator is used to negate the predicate that follows it.
If that following predicate is true, the NOT resolves to false.
Note
|
If the predicate is true, NOT resolves to false. If the predicate is unknown (e.g. |
The AND
operator is used to combine 2 predicate expressions.
The result of the AND expression is true if and only if both predicates resolve to true.
If either predicate resolves to unknown, the AND expression resolves to unknown as well. Otherwise, the result is false.
The OR
operator is used to combine 2 predicate expressions.
The result of the OR expression is true if one predicate resolves to true.
If both predicates resolve to unknown, the OR expression resolves to unknown.
Otherwise, the result is false.
The WHERE
clause of a query is made up of predicates which assert whether values in each potential row match the current filtering criteria.
Thus, the where clause restricts the results returned from a select query and limits the scope of update and delete queries.
The GROUP BY
clause allows building aggregated results for various value groups. As an example, consider the following queries:
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
The first query retrieves the complete total of all orders. The second retrieves the total for each customer, grouped by each customer.
In a grouped query, the where clause applies to the non-aggregated values (essentially it determines whether rows will make it into the aggregation).
The HAVING
clause also restricts results, but it operates on the aggregated values.
In the Group by example, we retrieved Call
duration totals for all persons.
If that ended up being too much data to deal with, we might want to restrict the results to focus only on customers with a summed total of more than 1000:
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
The HAVING
clause follows the same rules as the WHERE
clause and is also made up of predicates.
HAVING
is applied after the groupings and aggregations have been done, while the WHERE
clause is applied before.
The results of the query can also be ordered.
The ORDER BY
clause is used to specify the selected values to be used to order the result.
The types of expressions considered valid as part of the ORDER BY
clause include:
-
state fields
-
component/embeddable attributes
-
scalar expressions such as arithmetic operations, functions, etc.
-
identification variable declared in the select clause for any of the previous expression types
Additionally, JPQL says that all values referenced in the ORDER BY
clause must be named in the SELECT
clause.
HQL does not mandate that restriction, but applications desiring database portability should be aware that not all databases support referencing values in the ORDER BY
clause that are not referenced in the select clause.
Individual expressions in the order-by can be qualified with either ASC
(ascending) or DESC
(descending) to indicate the desired ordering direction.
Null values can be placed in front or at the end of the sorted set using NULLS FIRST
or NULLS LAST
clause respectively.
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
As explained in entity immutability section, fetching entities in read-only mode is much more efficient than fetching read-write entities. Even if the entities are mutable, you can still fetch them in read-only mode, and benefit from reducing the memory footprint and speeding up the flushing process.
Read-only entities are skipped by the dirty checking mechanism as illustrated by the following example:
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
link:extras/hql-read-only-entities-example.sql[role=include]
As you can see, there is no SQL UPDATE
being executed.
You can also pass the read-only hint to named queries using the Jakarta Persistence {jpaJavadocUrlPrefix}QueryHint.html[@QueryHint
] annotation.
link:../../../../../../main/java/org/hibernate/userguide/model/Person.java[role=include]
The Hibernate native API offers a Query#setReadOnly
method, as an alternative to using a Jakarta Persistence query hint:
link:../../../../../../test/java/org/hibernate/userguide/hql/HQLTest.java[role=include]
Any entity query, be it JPQL or Criteria API, has to be parsed into an AST (Abstract Syntax Tree) so that Hibernate can generate the proper SQL statement. The entity query compilation takes time, and for this reason, Hibernate offers a query plan cache.
When executing an entity query, Hibernate first checks the plan cache, and only if there’s no plan available, a new one will be computed right away.
The query plan cache can be configured via the following configuration properties:
hibernate.query.plan_cache_max_size
-
This setting gives the maximum number of entries of the plan cache. The default value is 2048.
hibernate.query.plan_parameter_metadata_max_size
-
The setting gives the maximum number of
ParameterMetadataImpl
instances maintained by the query plan cache. TheParameterMetadataImpl
object encapsulates metadata about parameters encountered within a query. The default value is 128.
Now, if you have many JPQL or Criteria API queries, it’s a good idea to increase the query plan cache size so that the vast majority of executing entity queries can skip the compilation phase, therefore reducing execution time.
To get a better understanding of the query plan cache effectiveness, Hibernate offers several statistics you can use. For more details, check out the Query plan cache statistics section.