Performing Date/Time Math In HQL?

Question

I\'m looking how to perform date/time math within an HQL query. Specifically, how do I add or subtract (x) amount of time from the result of the current_timestamp()

Answer 1

You could determine the syntax to do it using SQL in your database and then define a function within a custom HibernateDialect. For example, we needed a weekday function which is not standard SQL. We subclassed the dialect for each database and then added a line like this:

registerFunction("weekday", 
  new SQLFunctionTemplate(Hibernate.INTEGER, "to_char(?1,'D')") );

In your case, you could use a function called date_diff which might be defined as ? - ? in some databases or something different in others. That way you don't have to write raw SQL in your query and if you ever need to switch databases, you just map the function differently in your dialect.