Added a standard traverse-and-filter cache invalidator.

src/java/com/samskivert/jdbc/depot/CacheInvalidator.java

@@ -20,6 +20,8 @@
 
 package com.samskivert.jdbc.depot;
 
+import java.io.Serializable;
+
 /**
  * Implementors of this interface performs perform cache invalidation for calls to
  * {@link DepotRepository#updateLiteral}, {@link DepotRepository#updatePartial} and 
@@ -27,6 +29,30 @@ package com.samskivert.jdbc.depot;
  */
 public interface CacheInvalidator
 {
+    public static abstract class TraverseWithFilter<T extends Serializable>
+        implements CacheInvalidator
+    {
+        public TraverseWithFilter (Class<T> pClass) {
+            this(pClass.getName());
+        }
+
+        public TraverseWithFilter (String cacheId) {
+            _cacheId = cacheId;
+        }
+
+        public void invalidate (PersistenceContext ctx) {
+            ctx.cacheTraverse(_cacheId, new PersistenceContext.CacheEvictionFilter<T>() {
+                protected boolean testForEviction (Serializable key, T record) {
+                    return TraverseWithFilter.this.testForEviction(key, record);
+                }
+            });
+        }
+
+        protected abstract boolean testForEviction (Serializable key, T record);
+
+        protected String _cacheId;
+    }
+
     /**
      * Must invalidate all cache entries that depend on the records being modified or deleted.
      * This method is called just before the database statement is executed.