This is possibly getting a little too jiggy, but I'm having all Depot methods

that return a collection return an XList which extends List and adds the
method:

    public <R> Iterable<R> map (Function<T, R> mapper);

which allows you to do things the following:

    return findAll(CategoryRecord.class,
                   new Where(CategoryRecord.PARENT_ID.eq(parentId))).
            map(CategoryRecord.TO_CATEGORY);

which is sufficiently awesome that I think it merits taking these liberties.
Plus it opens the door to adding other transformations that one might want to
do with a collection just loaded from the database.

src/java/com/samskivert/depot/DepotRepository.java

@@ -264,7 +264,7 @@ public abstract class DepotRepository
      *
      * @throws DatabaseException if any problem is encountered communicating with the database.
      */
-    protected <T extends PersistentRecord> List<T> loadAll (
+    protected <T extends PersistentRecord> XList<T> loadAll (
         Class<T> type, Collection<? extends Comparable<?>> primaryKeys)
         throws DatabaseException
     {
@@ -282,10 +282,10 @@ public abstract class DepotRepository
      *
      * @throws DatabaseException if any problem is encountered communicating with the database.
      */
-    protected <T extends PersistentRecord> List<T> loadAll (Collection<Key<T>> keys)
+    protected <T extends PersistentRecord> XList<T> loadAll (Collection<Key<T>> keys)
         throws DatabaseException
     {
-        return (keys.size() == 0) ? Collections.<T>emptyList() :
+        return (keys.size() == 0) ? new XArrayList<T>() :
             _ctx.invoke(new FindAllQuery.WithKeys<T>(_ctx, keys));
     }
 
@@ -294,7 +294,7 @@ public abstract class DepotRepository
      *
      * @throws DatabaseException if any problem is encountered communicating with the database.
      */
-    protected <T extends PersistentRecord> List<T> findAll (Class<T> type, QueryClause... clauses)
+    protected <T extends PersistentRecord> XList<T> findAll (Class<T> type, QueryClause... clauses)
         throws DatabaseException
     {
         return findAll(type, Arrays.asList(clauses));
@@ -313,7 +313,7 @@ public abstract class DepotRepository
      *
      * @throws DatabaseException if any problem is encountered communicating with the database.
      */
-    protected <T extends PersistentRecord> List<T> findAll (
+    protected <T extends PersistentRecord> XList<T> findAll (
         Class<T> type, Collection<? extends QueryClause> clauses)
         throws DatabaseException
     {
@@ -325,7 +325,7 @@ public abstract class DepotRepository
      *
      * @throws DatabaseException if any problem is encountered communicating with the database.
      */
-    protected <T extends PersistentRecord> List<T> findAll (
+    protected <T extends PersistentRecord> XList<T> findAll (
         Class<T> type, CacheStrategy strategy, QueryClause... clauses)
         throws DatabaseException
     {
@@ -337,7 +337,7 @@ public abstract class DepotRepository
      *
      * @throws DatabaseException if any problem is encountered communicating with the database.
      */
-    protected <T extends PersistentRecord> List<T> findAll (
+    protected <T extends PersistentRecord> XList<T> findAll (
         Class<T> type, CacheStrategy cache, Collection<? extends QueryClause> clauses)
         throws DatabaseException
     {
@@ -395,7 +395,7 @@ public abstract class DepotRepository
      *
      * @throws DatabaseException if any problem is encountered communicating with the database.
      */
-    protected <T extends PersistentRecord> List<Key<T>> findAllKeys (
+    protected <T extends PersistentRecord> XList<Key<T>> findAllKeys (
         Class<T> type, boolean forUpdate, QueryClause... clause)
         throws DatabaseException
     {
@@ -413,7 +413,7 @@ public abstract class DepotRepository
      *
      * @throws DatabaseException if any problem is encountered communicating with the database.
      */
-    protected <T extends PersistentRecord> List<Key<T>> findAllKeys (
+    protected <T extends PersistentRecord> XList<Key<T>> findAllKeys (
         Class<T> type, boolean forUpdate, Collection<? extends QueryClause> clauses)
         throws DatabaseException
     {

src/java/com/samskivert/depot/XArrayList.java

@@ -0,0 +1,40 @@
+//
+// $Id$
+//
+// Depot library - a Java relational persistence library
+// Copyright (C) 2006-2009 Michael Bayne and Pär Winzell
+//
+// This library is free software; you can redistribute it and/or modify it
+// under the terms of the GNU Lesser General Public License as published
+// by the Free Software Foundation; either version 2.1 of the License, or
+// (at your option) any later version.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+// Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public
+// License along with this library; if not, write to the Free Software
+// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+
+package com.samskivert.depot;
+
+import java.util.ArrayList;
+
+import com.google.common.base.Function;
+import com.google.common.collect.Iterables;
+
+/**
+ * An array list specialization that implements {@link XList}. Depot returns this list from all of
+ * its methods to make it easy for callers to map the results to runtime records as desired.
+ */
+public class XArrayList<T> extends ArrayList<T>
+    implements XList<T>
+{
+    // from interface XList<T>
+    public <R> Iterable<R> map (Function<T, R> mapper)
+    {
+        return Iterables.transform(this, mapper);
+    }
+}

src/java/com/samskivert/depot/XList.java

@@ -0,0 +1,38 @@
+//
+// $Id$
+//
+// Depot library - a Java relational persistence library
+// Copyright (C) 2006-2009 Michael Bayne and Pär Winzell
+//
+// This library is free software; you can redistribute it and/or modify it
+// under the terms of the GNU Lesser General Public License as published
+// by the Free Software Foundation; either version 2.1 of the License, or
+// (at your option) any later version.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+// Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public
+// License along with this library; if not, write to the Free Software
+// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+
+package com.samskivert.depot;
+
+import java.util.List;
+
+import com.google.common.base.Function;
+
+/**
+ * Extends the {@link List} interface with a method {@link #map} that makes it easy to convert the
+ * contents of the list to an {@link Iterable} of a different type via the application of a {@link
+ * Function}.
+ */
+public interface XList<T> extends List<T>
+{
+    /**
+     * Returns an iterable over a mapping of this list via the specified mapping function.
+     */
+    public <R> Iterable<R> map (Function<T, R> mapper);
+}

src/java/com/samskivert/depot/impl/FindAllKeysQuery.java

@@ -21,15 +21,12 @@
 package com.samskivert.depot.impl;
 
 import java.util.Collection;
-import java.util.List;
 
 import java.sql.Connection;
 import java.sql.PreparedStatement;
 import java.sql.ResultSet;
 import java.sql.SQLException;
 
-import com.google.common.collect.Lists;
-
 import com.samskivert.jdbc.DatabaseLiaison;
 import com.samskivert.jdbc.JDBCUtil;
 
@@ -38,6 +35,8 @@ import com.samskivert.depot.Key;
 import com.samskivert.depot.PersistenceContext;
 import com.samskivert.depot.PersistentRecord;
 import com.samskivert.depot.Stats;
+import com.samskivert.depot.XArrayList;
+import com.samskivert.depot.XList;
 import com.samskivert.depot.clause.QueryClause;
 import com.samskivert.depot.clause.SelectClause;
 
@@ -46,7 +45,7 @@ import static com.samskivert.depot.Log.log;
 /**
  * Loads all primary keys for the records matching the supplied clause.
  */
-public class FindAllKeysQuery<T extends PersistentRecord> extends Query<List<Key<T>>>
+public class FindAllKeysQuery<T extends PersistentRecord> extends Query<XList<Key<T>>>
 {
     public FindAllKeysQuery (PersistenceContext ctx, Class<T> type, boolean forUpdate,
                              Collection<? extends QueryClause> clauses)
@@ -66,16 +65,16 @@ public class FindAllKeysQuery<T extends PersistentRecord> extends Query<List<Key
     }
 
     @Override // from Query
-    public List<Key<T>> getCachedResult (PersistenceContext ctx)
+    public XList<Key<T>> getCachedResult (PersistenceContext ctx)
     {
         return null; // TODO
     }
 
     // from Query
-    public List<Key<T>> invoke (PersistenceContext ctx, Connection conn, DatabaseLiaison liaison)
+    public XList<Key<T>> invoke (PersistenceContext ctx, Connection conn, DatabaseLiaison liaison)
         throws SQLException
     {
-        List<Key<T>> keys = Lists.newArrayList();
+        XList<Key<T>> keys = new XArrayList<Key<T>>();
         PreparedStatement stmt = _builder.prepare(conn);
         try {
             ResultSet rs = stmt.executeQuery();

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

@@ -48,6 +48,8 @@ import com.samskivert.depot.PersistenceContext;
 import com.samskivert.depot.PersistentRecord;
 import com.samskivert.depot.SimpleCacheKey;
 import com.samskivert.depot.Stats;
+import com.samskivert.depot.XArrayList;
+import com.samskivert.depot.XList;
 import com.samskivert.depot.clause.FieldOverride;
 import com.samskivert.depot.clause.QueryClause;
 import com.samskivert.depot.clause.SelectClause;
@@ -59,7 +61,7 @@ import static com.samskivert.depot.Log.log;
  * This class implements the functionality required by {@link DepotRepository#findAll}: fetch
  * a collection of persistent objects using one of two included strategies.
  */
-public abstract class FindAllQuery<T extends PersistentRecord> extends Query<List<T>>
+public abstract class FindAllQuery<T extends PersistentRecord> extends Query<XList<T>>
 {
     /**
      * The two-pass collection query implementation. See {@link DepotRepository#findAll} for
@@ -103,7 +105,7 @@ public abstract class FindAllQuery<T extends PersistentRecord> extends Query<Lis
         }
 
         @Override // from Query
-        public List<T> getCachedResult (PersistenceContext ctx)
+        public XList<T> getCachedResult (PersistenceContext ctx)
         {
             if (_qkey == null) {
                 return null;
@@ -118,7 +120,7 @@ public abstract class FindAllQuery<T extends PersistentRecord> extends Query<Lis
         }
 
         // from Query
-        public List<T> invoke (PersistenceContext ctx, Connection conn, DatabaseLiaison liaison)
+        public XList<T> invoke (PersistenceContext ctx, Connection conn, DatabaseLiaison liaison)
             throws SQLException
         {
             // we want this to remain null if our key set came from the cache
@@ -179,7 +181,7 @@ public abstract class FindAllQuery<T extends PersistentRecord> extends Query<Lis
         }
 
         @Override // from Query
-        public List<T> getCachedResult (PersistenceContext ctx)
+        public XList<T> getCachedResult (PersistenceContext ctx)
         {
             // look up what we can from the cache
             _fetchKeys = loadFromCache(ctx, _keys, _entities);
@@ -189,7 +191,7 @@ public abstract class FindAllQuery<T extends PersistentRecord> extends Query<Lis
         }
 
         // from Query
-        public List<T> invoke (PersistenceContext ctx, Connection conn, DatabaseLiaison liaison)
+        public XList<T> invoke (PersistenceContext ctx, Connection conn, DatabaseLiaison liaison)
             throws SQLException
         {
             return loadAndResolve(ctx, conn, _keys, _fetchKeys, _entities, null);
@@ -222,7 +224,7 @@ public abstract class FindAllQuery<T extends PersistentRecord> extends Query<Lis
         }
 
         @Override // from Query
-        public List<T> getCachedResult (PersistenceContext ctx)
+        public XList<T> getCachedResult (PersistenceContext ctx)
         {
             if (_qkey != null) {
                 _cachedQueries++;
@@ -232,10 +234,10 @@ public abstract class FindAllQuery<T extends PersistentRecord> extends Query<Lis
         }
 
         // from Query
-        public List<T> invoke (PersistenceContext ctx, Connection conn, DatabaseLiaison liaison)
+        public XList<T> invoke (PersistenceContext ctx, Connection conn, DatabaseLiaison liaison)
             throws SQLException
         {
-            List<T> result = Lists.newArrayList();
+            XList<T> result = new XArrayList<T>();
             SQLBuilder builder = ctx.getSQLBuilder(DepotTypes.getDepotTypes(ctx, _select));
             builder.newQuery(_select);
             PreparedStatement stmt = builder.prepare(conn);
@@ -297,9 +299,9 @@ public abstract class FindAllQuery<T extends PersistentRecord> extends Query<Lis
         return fetchKeys;
     }
 
-    protected List<T> resolve (Iterable<Key<T>> allKeys, Map<Key<T>, T> entities)
+    protected XList<T> resolve (Iterable<Key<T>> allKeys, Map<Key<T>, T> entities)
     {
-        List<T> result = Lists.newArrayList();
+        XList<T> result = new XArrayList<T>();
         for (Key<T> key : allKeys) {
             T value = entities.get(key);
             if (value != null) {
@@ -309,9 +311,9 @@ public abstract class FindAllQuery<T extends PersistentRecord> extends Query<Lis
         return result;
     }
 
-    protected List<T> loadAndResolve (PersistenceContext ctx, Connection conn,
+    protected XList<T> loadAndResolve (PersistenceContext ctx, Connection conn,
-                                      Iterable<Key<T>> allKeys, Set<Key<T>> fetchKeys,
+                                       Iterable<Key<T>> allKeys, Set<Key<T>> fetchKeys,
-                                      Map<Key<T>, T> entities, String origStmt)
+                                       Map<Key<T>, T> entities, String origStmt)
         throws SQLException
     {
         if (PersistenceContext.CACHE_DEBUG && fetchKeys.size() > 0) {