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228 CHAPTER 11 n FILTERING THE RESULTS OF SEARCHES CHAPTER 11 n FILTERING THE RESULTS OF SEARCHES to map values to parameters. Once you have defined your filter, you need to attach the filter definition to a class. At the end of our User class definition, we specify that it uses a filter named activatedFilter. We then need to set a condition corresponding to an HQL WHERE clause for the attached filter. In our case, we used :activatedParam = activated, where :activatedParam is the named parameter specified on the filter definition, and activated is the column name from the user table. You should ensure that the named parameter goes on the left-hand side so that Hibernate s generated SQL doesn t interfere with any joins. Listing 11-1. Hibernate XML Mapping for User
With the filter definition created and attached to a class with a suitable condition, we need to activate the filter. The next class, SimpleFilterExample, inserts several user records into the database, and then immediately displays them to the screen. The class uses a very simple HQL query (from User) to obtain the result set from Hibernate. The displayUsers() method writes the usernames and activation status out to the console. Before you have enabled any filters on the database, this method will return the full list of users. Once you have enabled the first filter (activatedFilter) to show only activated users, call the same displayUsers() method the results of the query are the same as if you had added a WHERE clause containing an “activated=true” clause. You can just as easily change the filter s parameter value to show inactive users, as shown in Listing 11-2.
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