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  package org.apache.cayenne.reflect;
  
  import java.util.Collection;
  
  import org.apache.cayenne.Fault;
  import org.apache.cayenne.ValueHolder;
  import org.apache.cayenne.util.PersistentObjectCollection;
  
  /**
   * A generic superclass of CollectionProperty implementations.
   * 
   * @since 1.2
   */
  public abstract class BaseToManyProperty extends BaseArcProperty implements
          ToManyProperty {
  
      public BaseToManyProperty(ClassDescriptor owner, ClassDescriptor targetDescriptor,
              Accessor accessor, String reverseName) {
          super(owner, targetDescriptor, accessor, reverseName);
      }
  
      @Override
      public Object readProperty(Object object) throws PropertyException {
          return ensureCollectionValueHolderSet(object);
      }
  
      /**
       * Wraps list in a value holder that performs lazy faulting.
       */
      @Override
      public void writePropertyDirectly(Object object, Object oldValue, Object newValue)
              throws PropertyException {
  
          if (newValue instanceof Fault) {
              super.writePropertyDirectly(object, null, newValue);
          }
          else {
              // must resolve value holder...
              ValueHolder holder = (ValueHolder) readProperty(object);
              holder.setValueDirectly(newValue);
          }
      }
  
      public void addTarget(Object source, Object target, boolean setReverse) {
          if (target == null) {
              throw new NullPointerException("Attempt to add null object.");
          }
  
          // TODO, Andrus, 2/9/2006 - GenericPersistentObject differences:
          // * invokes "willConnect"
          // * has a callback to ObjectStore to handle flattened
          // * has a callback to ObjectStore to retain snapshot
          // * changes object state to modified
  
          // Now do the rest of the normal handling (regardless of whether it was
          // flattened or not)
          Collection<Object> collection = (Collection<Object>) readProperty(source);
          collection.add(target);
  
          if (setReverse) {
              setReverse(source, null, target);
          }
      }
      
      public void addTargetDirectly(Object source, Object target) throws PropertyException {
          ((PersistentObjectCollection) readProperty(source)).addDirectly(target);
      }
      
      public void removeTargetDirectly(Object source, Object target) throws PropertyException {
          ((PersistentObjectCollection) readProperty(source)).removeDirectly(target);
      }
  
      public void removeTarget(Object source, Object target, boolean setReverse) {
  
          // TODO, Andrus, 2/9/2006 - GenericPersistentObject differences:
          // * has a callback to ObjectStore to handle flattened
          // * changes object state to modified
  
          // Now do the rest of the normal handling (regardless of whether it was
          // flattened or not)
          Collection<Object> collection = (Collection<Object>) readProperty(source);
          collection.remove(target);
  
          if (target != null && setReverse) {
              setReverse(source, target, null);
          }
      }
  
      @Override
      public boolean visit(PropertyVisitor visitor) {
          return visitor.visitToMany(this);
      }
  
      /**
       * Injects a List in the object if it hasn't been done yet.
       */
      @Override
      public void injectValueHolder(Object object) throws PropertyException {
          ensureCollectionValueHolderSet(object);
      }
  
      /**
       * Checks that an object's List field described by this property is set, injecting a
       * List if needed.
       */
      protected ValueHolder ensureCollectionValueHolderSet(Object object)
              throws PropertyException {
  
          Object value = accessor.getValue(object);
  
          if (value == null || value instanceof Fault) {
              value = createCollectionValueHolder(object);
              accessor.setValue(object, value);
          }
  
          return (ValueHolder) value;
      }
  
      /**
       * Creates a Collection for an object.
       */
      protected abstract ValueHolder createCollectionValueHolder(Object object)
              throws PropertyException;
      
  }
  