... table-per-subclass mapping, 57 plugin descriptorsmetadata and, 371 – 373 supplying hooks with, 374 – 375 plugin systemcommandsfor discovery, 3 67 369for installation, 369– 370 local plugins, 370 overview ... fields, 193–1 97 event handling, 178 – 179 executing code before and after calls, 177 – 178 flow of request, 172 HTML anchor tag, creating, 173 – 174 login request, handling, 176 overview of, 171 performance ... 87 ■Hhalting execution with before interceptor, 91handling validation errors, 79 handling eventsAjax, 178 – 179 hasErrors() method, 79 hasErrors tag, 1 17, 124hashCode, implementing, 276 – 277 hashing...