Hibernate Dialects + datediff function

问题

I have a problem in that the syntax for datediff in mysql is different from that in hsqldb:

mysql: datediff(date1,date2)
hsqldb: datediff(interval,date1,date2)

The dialects in hibernate usually resolve these issues, however I don't seem to be able to find a way of creating a datediff restriction for hibernate. This is a real nuisance because it prevents me from unit testing with an in-memory hsql database since I have to 'hardcode' the format of datediff in a sql statement.

If anyone has advice on this matter it would be greatly appreciated.

回答1:

I would say that the easiest solution is to create your own custom HSQLDB dialect, extending the existing HSQLDB dialect. Then, in the constructor, register a function to handle datediff(date1, date2) to be translated into datediff(interval, date1, date2), provided that interval would be a static value. Something like this:

registerFunction( "datediff", new SQLFunctionTemplate( StandardBasicTypes.INTEGER, "datediff(interval, ?1, ?2)" ) );

来源：https://stackoverflow.com/questions/4606807/hibernate-dialects-datediff-function