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Plugin for DataNucleus providing persistence to the Google AppEngine BigTable datastore
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/*
 * Copyright (C) 2010 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.appengine.datanucleus;

import com.google.appengine.api.datastore.Cursor;
import com.google.appengine.api.datastore.Entity;
import com.google.appengine.api.datastore.FetchOptions;
import com.google.appengine.api.datastore.Key;
import com.google.appengine.api.datastore.PreparedQuery;
import com.google.appengine.api.datastore.QueryResultIterable;
import com.google.appengine.api.datastore.QueryResultList;

import org.datanucleus.ClassLoaderResolver;
import org.datanucleus.api.jpa.JPAEntityManager;
import org.datanucleus.metadata.AbstractClassMetaData;
import org.datanucleus.store.ExecutionContext;
import org.datanucleus.store.ObjectProvider;

import java.util.List;

import javax.persistence.EntityManager;

/**
 * Utilities for converting between the low-level datastore api and JPA. 

 * This class is part of the public api of the DataNucleus App Engine plugin and can be safely used.
 *
 * @author Max Ross 
 */
public final class JPADatastoreBridge extends PojoDatastoreBridge {

  /**
   * Convert the result of a low-level datastore query into a List of JPA
   * entities.
   *
   * @param em The EntityManager with which the conversion results will be associated.
   * @param cls The type of object to which the {@link Entity Entities} in the
   * result list should be converted.
   * @param queryResultList The result of the low-level datastore query.
   * @return The {@link Entity Entities} in the provided result list, converted to JPA entities.
   *
   * @see PreparedQuery#asQueryResultList(FetchOptions)
   */
  public  List toJPAResult(EntityManager em, Class cls, QueryResultList queryResultList) {
    return toJPAResult(em, cls, queryResultList, queryResultList.getCursor());
  }

  /**
   * Convert the result of a low-level datastore query into a List of JPA entities.
   *
   * @param em The EntityManager with which the conversion results will be associated.
   * @param cls The type of object to which the {@link Entity Entities} in the
   * result iterable should be converted.
   * @param queryResultIterable The result of the low-level datastore query.
   * @return The {@link Entity Entities} in the provided result iterable, converted to JPA entities.
   *
   * @see PreparedQuery#asQueryResultIterable()
   */
  public  List toJPAResult(EntityManager em, Class cls, QueryResultIterable queryResultIterable) {
    return toJPAResult(em, cls, queryResultIterable, null);
  }

  private  List toJPAResult(EntityManager em, Class cls, Iterable queryResultIterable, Cursor endCursor) {
    ExecutionContext ec = ((JPAEntityManager) em).getExecutionContext();
    return toPojoResult(ec, cls, queryResultIterable, endCursor);
  }

  /**
   * Convenience method to return the Entity for this managed JDO object.
   * @param pc The JDO object (managed by the provided PM)
   * @param pm The Persistence Manager
   * @return The Entity (if accessible)
   */
  public Entity getEntityFromJPA(Object pc, EntityManager em) {
    ExecutionContext ec = ((JPAEntityManager)em).getExecutionContext();
    ObjectProvider op = ec.findObjectProvider(pc);
    if (op != null) {
      DatastoreManager storeMgr = (DatastoreManager) ec.getStoreManager();
      DatastoreTransaction txn = storeMgr.getDatastoreTransaction(ec);
      if (txn != null) {
        Entity entity = (Entity)op.getAssociatedValue(txn);
        if (entity != null) {
          return entity;
        } else {
          Key key = EntityUtils.getPkAsKey(op);
          return EntityUtils.getEntityFromDatastore(storeMgr.getDatastoreServiceForReads(ec), op, key);
        }
      } else {
        Key key = EntityUtils.getPkAsKey(op);
        return EntityUtils.getEntityFromDatastore(storeMgr.getDatastoreServiceForReads(ec), op, key);
      }
    } else {
      // TODO Cater for detached objects
      throw new UnsupportedOperationException("Not yet supported getting Entity for detached/unmanaged object");
    }
  }

  /**
   * Convenience method to return a managed (POJO) object for the provided Entity for the EntityManager.
   * @param entity The entity
   * @param em The EntityManager
   * @param cls The POJO class being represented here
   * @return The POJO
   */
  public Object getJPAFromEntity(Entity entity, EntityManager em, Class cls) {
    ExecutionContext ec = ((JPAEntityManager)em).getExecutionContext();
    ClassLoaderResolver clr = ec.getClassLoaderResolver();
    AbstractClassMetaData cmd = ec.getMetaDataManager().getMetaDataForClass(cls, clr);
    return EntityUtils.entityToPojo(entity, cmd, clr, ec, false, ec.getFetchPlan());
  }
}