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   *  distributed with this work for additional information
   *  regarding copyright ownership.  The ASF licenses this file
   *  to you under the Apache License, Version 2.0 (the
   *  "License"); you may not use this file except in compliance
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   *
   *    https://www.apache.org/licenses/LICENSE-2.0
   *
   *  Unless required by applicable law or agreed to in writing,
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   *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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  package org.apache.cayenne.reflect;
  
  import java.util.Map;
  
  import org.apache.cayenne.ObjectId;
  import org.apache.cayenne.Persistent;
  
  /**
   * A stateless read-only accessor of the map key value that is based on the Persistent
   * object id. For single-column ID's the accessor returns a single value (e.g. an
   * Integer). For multi-column ID's it returns the ObjectId.
   * 
   * @since 3.0
   */
  public class IdMapKeyAccessor implements Accessor {
  
      public static final Accessor SHARED_ACCESSOR = new IdMapKeyAccessor();
  
      public String getName() {
          return "IdMapKeyAccessor";
      }
  
      public Object getValue(Object object) throws PropertyException {
          if (object instanceof Persistent) {
              ObjectId id = ((Persistent) object).getObjectId();
  
              if (id.isTemporary()) {
                  return id;
              }
  
              Map<?, ?> map = id.getIdSnapshot();
              if (map.size() == 1) {
                  Map.Entry<?, ?> pkEntry = map.entrySet().iterator().next();
                  return pkEntry.getValue();
              }
  
              return id;
          }
          else {
              throw new IllegalArgumentException("Object must be Persistent: " + object);
          }
      }
  
      public void setValue(Object object, Object newValue) throws PropertyException {
          throw new UnsupportedOperationException("Setting map key is not supported");
      }
  }
  