diff --git a/src/main/java/com/google/gwtorm/client/CompoundKey.java b/src/main/java/com/google/gwtorm/client/CompoundKey.java
new file mode 100644
index 0000000..d1e5341
--- /dev/null
+++ b/src/main/java/com/google/gwtorm/client/CompoundKey.java
@@ -0,0 +1,101 @@
+// Copyright 2008 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gwtorm.client;
+
+import java.io.Serializable;
+
+/**
+ * Abstract key type composed of other keys.
+ * <p>
+ * Applications should subclass this type to create their own entity-specific
+ * key classes.
+ * 
+ * @param <P> the parent key type. Use {@link Key} if no parent key is needed.
+ */
+public abstract class CompoundKey<P extends Key<?>> implements Key<P>,
+    Serializable {
+  /** @return the member key components, minus the parent key. */
+  public abstract Key<?>[] members();
+
+  /**
+   * @return the parent key instance; null if this is a root level key.
+   */
+  public P getParentKey() {
+    return null;
+  }
+
+  @Override
+  public int hashCode() {
+    int hc = 0;
+    if (getParentKey() != null) {
+      hc = getParentKey().hashCode();
+    }
+    for (final Key<?> k : members()) {
+      hc *= 31;
+      hc += k.hashCode();
+    }
+    return hc;
+  }
+
+  @Override
+  public boolean equals(final Object b) {
+    if (b == null || b.getClass() != getClass()) {
+      return false;
+    }
+
+    final CompoundKey<P> q = cast(b);
+    if (getParentKey() != null && !getParentKey().equals(q.getParentKey())) {
+      return false;
+    }
+
+    final Key<?>[] aMembers = members();
+    final Key<?>[] bMembers = q.members();
+    if (aMembers.length != bMembers.length) {
+      return false;
+    }
+    for (int i = 0; i < aMembers.length; i++) {
+      if (!aMembers[i].equals(bMembers[i])) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  @Override
+  public String toString() {
+    final StringBuffer r = new StringBuffer();
+    r.append(getClass().getName());
+    r.append('[');
+    boolean first = true;
+    if (getParentKey() != null) {
+      r.append(getParentKey().toString());
+      first = false;
+    }
+    for (final Key<?> k : members()){
+      if (!first) {
+        r.append(", ");
+      }
+      r.append(k.toString());
+      first = false;
+    }
+    r.append(']');
+    return r.toString();
+  }
+
+  @SuppressWarnings("unchecked")
+  private static <A extends Key<?>> CompoundKey<A> cast(final Object b) {
+    return (CompoundKey<A>) b;
+  }
+}