[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=eyJpIjoiOThlODEwMmE1ZjljNDIwYWFkNzM3NWU5NmIwNWI4OWMiLCJwIjoiaiJ9 ) / New Feature ( https://hibernate.atlassian.net/browse/HHH-14051?atlOrigin=eyJpIjoiOThlODEwMmE1ZjljNDIwYWFkNzM3NWU5NmIwNWI4OWMiLCJwIjoiaiJ9 ) HHH-14051 ( https://hibernate.atlassian.net/browse/HHH-14051?atlOrigin=eyJpIjoiOThlODEwMmE1ZjljNDIwYWFkNzM3NWU5NmIwNWI4OWMiLCJwIjoiaiJ9 ) typesafe references to named queries, result set mappings, and entity graphs ( https://hibernate.atlassian.net/browse/HHH-14051?atlOrigin=eyJpIjoiOThlODEwMmE1ZjljNDIwYWFkNzM3NWU5NmIwNWI4OWMiLCJwIjoiaiJ9 )

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=eyJpIjoiOThlODEwMmE1ZjljNDIwYWFkNzM3NWU5NmIwNWI4OWMiLCJwIjoiaiJ9 ) Add Comment ( https://hibernate.atlassian.net/browse/HHH-14051#add-comment?atlOrigin=eyJpIjoiOThlODEwMmE1ZjljNDIwYWFkNzM3NWU5NmIwNWI4OWMiLCJwIjoiaiJ9 )

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