So while the JRE is happy to serialize arrays, EHCache is reluctant to do so in at least one place (presumably an explicit Serializable test). Let's switch to an ArrayList until further notice.

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

@@ -72,10 +72,9 @@ public class BindVisitor implements ExpressionVisitor
     public void visit (WhereCondition<? extends PersistentRecord> whereCondition)
         throws Exception
     {
-        Comparable[] values = whereCondition.getValues();
-        for (int ii = 0; ii < values.length; ii ++) {
-            if (values[ii] != null) {
-                _stmt.setObject(_argIdx ++, values[ii]);
+        for (Comparable value : whereCondition.getValues()) {
+            if (value != null) {
+                _stmt.setObject(_argIdx ++, value);
             }
         }
     }

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

@@ -21,6 +21,7 @@
 package com.samskivert.jdbc.depot;
 
 import java.sql.SQLException;
+import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -98,7 +99,7 @@ public abstract class BuildVisitor implements ExpressionVisitor
     {
         Class<? extends PersistentRecord> pClass = whereCondition.getPersistentClass();
         String[] keyFields = Key.getKeyFields(pClass);
-        Comparable[] values = whereCondition.getValues();
+        List<Comparable> values = whereCondition.getValues();
         for (int ii = 0; ii < keyFields.length; ii ++) {
             if (ii > 0) {
                 _builder.append(" and ");
@@ -109,7 +110,7 @@ public abstract class BuildVisitor implements ExpressionVisitor
             _enableOverrides = true;
             appendRhsColumn(pClass, keyFields[ii]);
             _enableOverrides = saved;
-            _builder.append(values[ii] == null ? " is null " : " = ? ");
+            _builder.append(values.get(ii) == null ? " is null " : " = ? ");
         }
     }
 

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

@@ -117,7 +117,7 @@ public abstract class FindAllQuery<T extends PersistentRecord>
                     // Single-column keys result in the compact IN(keyVal1, keyVal2, ...)
                     Comparable[] keyFieldValues = new Comparable[fetchKeys.size()];
                     for (int ii = 0; ii < keyFieldValues.length; ii ++) {
-                        keyFieldValues[ii] = fetchKeys.get(ii).condition.getValues()[0];
+                        keyFieldValues[ii] = fetchKeys.get(ii).condition.getValues().get(0);
                     }
                     condition = new In(_type, _marsh.getPrimaryKeyFields()[0], keyFieldValues);
 

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

@@ -23,7 +23,6 @@ package com.samskivert.jdbc.depot;
 import java.io.Serializable;
 import java.lang.reflect.Field;
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.Collection;
 import java.util.HashMap;
 import java.util.Map;
@@ -44,9 +43,10 @@ public class Key<T extends PersistentRecord> extends WhereClause
     implements SQLExpression, CacheKey, ValidatingCacheInvalidator, Serializable
 {
     /** An expression that contains our key columns and values. */
-    public static class WhereCondition<U extends PersistentRecord> implements SQLExpression
+    public static class WhereCondition<U extends PersistentRecord>
+        implements SQLExpression, Serializable
     {
-        public WhereCondition (Class<U> pClass, Comparable[] values)
+        public WhereCondition (Class<U> pClass, ArrayList<Comparable> values)
         {
             _pClass = pClass;
             _values = values;
@@ -69,7 +69,7 @@ public class Key<T extends PersistentRecord> extends WhereClause
             return _pClass;
         }
 
-        public Comparable[] getValues ()
+        public ArrayList<Comparable> getValues ()
         {
             return _values;
         }
@@ -84,17 +84,17 @@ public class Key<T extends PersistentRecord> extends WhereClause
                 return false;
             }
             WhereCondition other = (WhereCondition) obj;
-            return _pClass == other._pClass && Arrays.equals(_values, other._values);
+            return _pClass == other._pClass && _values.equals(other.getValues());
         }
 
         @Override
         public int hashCode ()
         {
-            return _pClass.hashCode() ^ Arrays.hashCode(_values);
+            return _pClass.hashCode() ^ _values.hashCode();
         }
 
         protected Class<U> _pClass;
-        protected Comparable[] _values;
+        protected ArrayList<Comparable> _values;
     }
 
     /** The expression that identifies our row. */
@@ -145,13 +145,19 @@ public class Key<T extends PersistentRecord> extends WhereClause
         String[] keyFields = getKeyFields(pClass);
 
         // now extract the values in field order and ensure none are extra or missing
-        Comparable[] newValues = new Comparable[fields.length];
+        ArrayList<Comparable> newValues = new ArrayList<Comparable>();
         for (int ii = 0; ii < keyFields.length; ii++) {
-            newValues[ii] = map.remove(keyFields[ii]);
-            // make sure we were provided with a value for this primary key field
-            if (newValues[ii] == null) {
+            Comparable nugget = map.remove(keyFields[ii]);
+            if (nugget == null) {
+                // make sure we were provided with a value for this primary key field
                 throw new IllegalArgumentException("Missing value for key field: " + keyFields[ii]);
             }
+            if (nugget instanceof Serializable) {
+                newValues.add(nugget);
+                continue;
+            }
+            throw new IllegalArgumentException(
+                "Non-serializable argument [key=" + keyFields[ii] + ", arg=" + nugget + "]");
         }
 
         // finally make sure we were not given any fields that are not in fact primary key fields
@@ -185,7 +191,7 @@ public class Key<T extends PersistentRecord> extends WhereClause
     // from CacheKey
     public Serializable getCacheKey ()
     {
-        return this; // TODO: Optimally return a special class here containing only _values.
+        return condition.getValues();
     }
 
     // from ValidatingCacheInvalidator
@@ -240,7 +246,7 @@ public class Key<T extends PersistentRecord> extends WhereClause
             if (ii > 0) {
                 builder.append(", ");
             }
-            builder.append(keyFields[ii]).append("=").append(condition.getValues()[ii]);
+            builder.append(keyFields[ii]).append("=").append(condition.getValues().get(ii));
         }
         builder.append(")");
         return builder.toString();