[hibernate-dev] Difference between Comment and Hint in Hibernate query

[Steve Ebersole]

See inline..

On Tue, Aug 1, 2017 at 9:05 AM Vlad Mihalcea <mihalcea.vlad at gmail.com>
wrote:

> I created a new Pull Request so that comments can be handled for named
> queries (even for UPDATE/DELETE queries):
>
> https://github.com/hibernate/hibernate-orm/pull/1970
>

Not really following this.  See
`org.hibernate.annotations.NamedQuery#comment` and
`org.hibernate.annotations.QueryHints#COMMENT`.  So we do support this for
named queries.  Hints are generally only useful (if at all) for SELECTs.
Comments can be useful for any type of statement, but again we have the
support for those in place in regards to named queries.


I think we should add two new issues;
>
> 1. So that we could pass Query Hints for Named (Native) Queries as well.
> Right now we can only pass comments which are appended at the beginning of
> the SQL statement.
>

I completely disagree about supporting comments and/or hints for native SQL
queries.

As for "[we only support] comments which are appended at the beginning of
the SQL statement" - that is true for comments.  However, it is inaccurate
for hints - see `org.hibernate.dialect.Dialect#getQueryHintString`.  So the
hook is in place for handling this for hints.  There is no such hook for
comments - do you concretely know of a Dialect that supports a comment
elsewhere than the start?  I'm a little leery of adding support for this
pre-6.0 as we know for certain that this will change (String-based versus
AST-based).  If you wan to add such a hook in 6.0, I am ok with that -
provided you can show me such a concrete use case.




> 2. I see we support Query Hints for Oracle and SQL Server. We should
> support MySQL as well:
>
> https://dev.mysql.com/doc/refman/5.7/en/optimizer-hints.html
>

Sure - I think its a good idea to support this where ever  the underlying
database supports it.


If you have time to take a look on the PR, let me know what you think.
>

I'll take a look at the PR after we resolve these general points and they
are incorporated into the PR.