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fix section on getSingleResultOrNull()

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Gavin 2023-05-14 12:48:48 +02:00 committed by Christian Beikov
parent a3cd3a9839
commit 1c2c14ff70
1 changed files with 5 additions and 3 deletions
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8
documentation/src/main/asciidoc/introduction/Interacting.adoc
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@ -383,7 +383,7 @@ It's not necessary to dirty-check on entity instance in read-only mode.
Hibernate features three complementary ways to write queries: Hibernate features three complementary ways to write queries:
- the _Hibernate Query Language_, an extremely powerful superset of JPQL, which abstracts most of the features of modern SQL queries, - the _Hibernate Query Language_, an extremely powerful superset of JPQL, which abstracts most of the features of modern dialects of SQL,
- the JPA _criteria query_ API, along with extensions, allowing almost any HQL query to be constructed programmatically via a typesafe API, and, of course - the JPA _criteria query_ API, along with extensions, allowing almost any HQL query to be constructed programmatically via a typesafe API, and, of course
- for when all else fails, _native SQL_ queries. - for when all else fails, _native SQL_ queries.
@ -393,7 +393,7 @@ Hibernate features three complementary ways to write queries:
:hql: https://docs.jboss.org/hibernate/orm/6.2/userguide/html_single/Hibernate_User_Guide.html#query-language :hql: https://docs.jboss.org/hibernate/orm/6.2/userguide/html_single/Hibernate_User_Guide.html#query-language
A full discussion of the query language would require just as much text as the rest of this Introduction. A full discussion of the query language would require just as much text as the rest of this Introduction.
Fortunately, HQL is already described in exhaustive detail in the {hql}[User Guide]. Fortunately, HQL is already described in exhaustive (and exhausting) detail in the {hql}[User Guide].
// The query language is discussed in great detail below in <<query-language>>. // The query language is discussed in great detail below in <<query-language>>.
Here we want to see how to execute a query via the `Session` or `EntityManager` API. Here we want to see how to execute a query via the `Session` or `EntityManager` API.
@ -472,9 +472,11 @@ Or, if we're expecting it to return at most one result, we can use `getSingleRes
Book bookOrNull = Book bookOrNull =
s.createSelectionQuery("from Book where isbn = ?1", Book.class) s.createSelectionQuery("from Book where isbn = ?1", Book.class)
.setParameter(1, isbn) .setParameter(1, isbn)
.getSingleResult(); .getSingleResultOrNull();
---- ----
The difference, of course, is that `getSingleResult()` throws an exception if there is no matching row in the database, whereas `getSingleResultOrNull()` just returns `null`.
By default, Hibernate dirty checks entities in the persistence context before executing a query, in order to determine if the session should be flushed. By default, Hibernate dirty checks entities in the persistence context before executing a query, in order to determine if the session should be flushed.
If there are many entities association with the persistence context, then this can be an expensive operation. If there are many entities association with the persistence context, then this can be an expensive operation.