Stupid Hibernate Tricks

I've recently been finding myself looking for a way to get Hibernate to override the default type for strings (varchar) and use char instead in order to boost performance of the database for fields that I know are going to have a fixed length. During my search, I came upon a couple of solutions.

Using annotations

You can use the 'columnDefinition' attribute of the @Column annotation to specify the SQL type directly. This has the unfortunate side effective of possibly reducing the database portability of your application.

Using SQL Dialects

You can override one of Hibernate's built in SQL Dialects and make char() types the default for strings. One other interesting possibility this opens up is that it allows you to only override the definition for certain lengths, ie, you could make any strings less than or equal to 4 characters in length use a char() definition, and the rest could use varchar definitions. This is done using the 'registerColumnType' method of Dialect.