[hibernate-issues] [JIRA] (HHH-14051) typesafe references to named queries, result set mappings, and entity graphs

[Gavin King (JIRA)]

Gavin King ( https://hibernate.atlassian.net/secure/ViewProfile.jspa?accountId=5ed39290d986a30c29c69002 ) *updated* an issue

Hibernate ORM ( https://hibernate.atlassian.net/browse/HHH?atlOrigin=eyJpIjoiYzUyMWQxMTkzMGVlNGM4YTk2MjIzYTZlZWUwZGI0OWMiLCJwIjoiaiJ9 ) / New Feature ( https://hibernate.atlassian.net/browse/HHH-14051?atlOrigin=eyJpIjoiYzUyMWQxMTkzMGVlNGM4YTk2MjIzYTZlZWUwZGI0OWMiLCJwIjoiaiJ9 ) HHH-14051 ( https://hibernate.atlassian.net/browse/HHH-14051?atlOrigin=eyJpIjoiYzUyMWQxMTkzMGVlNGM4YTk2MjIzYTZlZWUwZGI0OWMiLCJwIjoiaiJ9 ) typesafe references to named queries, result set mappings, and entity graphs ( https://hibernate.atlassian.net/browse/HHH-14051?atlOrigin=eyJpIjoiYzUyMWQxMTkzMGVlNGM4YTk2MjIzYTZlZWUwZGI0OWMiLCJwIjoiaiJ9 )

Change By: Gavin King ( https://hibernate.atlassian.net/secure/ViewProfile.jspa?accountId=5ed39290d986a30c29c69002 )

Currently, named queries, entity graphs, and SQL result set mappings are identified by stringly-typed keys.

It would be better if the metamodel generator would generate a typesafe element that identifies each of these things defined within a certain persistence unit. The reference can in principle even encode the result type of the query.

Thus, you would be able to write:

{{TypedQuery<Book> q =  book session.createNamedQuery(NamedQueries_.bookWithAuthor);}}

Or:

{{TypedQuery<Book> q =  book session.createNativeQuery(sqlQuery, ResultSetMappings_.bookWithAuthor);}}

Or:

{{Book book = session.find(Book.class, EntityGraphs_.bookWithAuthor);}}

Or whatever, and have that all be completely typesafe.

Now, a challenge for this is how to determine the "return type" for each sort of thing.

* For {{@SqlResultSetMapping}} and {{@NamedNativeQuery}}, it's explicit in the annotation.
* For {{@NamedEntityGraph}}, it could reasonably be inferred from the entity class on which the annotation occurs.
* For {{@NamedQuery}} we have a problem.

Now, the query-validator project shows how it's in-principle possible to typecheck a named JPA query at compile time, however, that approach is currently limited to Java 8.

There do seem to be some clever ways to infer the result type of a {{@NamedQuery}} in specific cases, without typechecking the entire query. For example:

* If there's more than one element in the {{select}}, it's totally trivial (must be {{Object[]}}).
* If there's no {{select}} clause at all, the problem is also pretty easy: either you've got a {{from}} with no {{join}}, in which case the thing after {{from}} is the name of the entity, or you have a {{from}} and a {{join}}, in which case you're back to {{Object[]}}.

However, for the specific case of exactly one element in the ` {{select}} ` clause, we have a problem.

So one option would be to add a result type member to the Hibernate {{@NamedQuery}} annotation, so that the user can specify it explicitly (defaulting to {{Object}}, of course).

Ultimately this would be a great feature to contribute back to the JPA spec.

( https://hibernate.atlassian.net/browse/HHH-14051#add-comment?atlOrigin=eyJpIjoiYzUyMWQxMTkzMGVlNGM4YTk2MjIzYTZlZWUwZGI0OWMiLCJwIjoiaiJ9 ) Add Comment ( https://hibernate.atlassian.net/browse/HHH-14051#add-comment?atlOrigin=eyJpIjoiYzUyMWQxMTkzMGVlNGM4YTk2MjIzYTZlZWUwZGI0OWMiLCJwIjoiaiJ9 )

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