/**
 *    Copyright 2011 meltmedia
 *
 *    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 org.xchain.namespaces.hibernate;

import org.apache.commons.jxpath.JXPathContext;
import org.hibernate.Query;
import org.xchain.annotations.Element;

/**
 * <p>The <code>unique-result</code> evaluates a query as a uniqueResult.</p>
 * 
 * <p>This must reference a <code>query</code>.</p>
 * 
 * <code class="source">
 * <xchain:session xmlns:xchain="http://www.xchain.org/hibernate/1.0">
 *  <xchain:transaction>
 *    ...
 *    <xchain:query query="'from Entity where value = 1'">
 *      ...
 *      <unique-result result="$myEntity"/>
 *      ...
 *    </xchain:query>
 *    ...
 *  </xchain:transaction>
 * </xchain:session>
 * </code> 
 *
 * @author Devon Tackett
 * @author Christian Trimble
 * 
 * @see QueryCommand
 * @see org.hibernate.Query
 * @see org.hibernate.Query#uniqueResult()
 */
@Element(localName="unique-result")
public abstract class UniqueResultCommand 
	extends AbstractQueryResultCommand
{ 	  
	  /**
	   * Evaluates the query as a unique-result.
	   */
	  public boolean execute( JXPathContext context )
	    throws Exception
	  { 
	    Query query = getQuery(context);
	    
		  if (query == null)
			  throw new Exception("A unique-result command must have a query.");
		  
    	// Execute the query and store the result.
    	storeValue(context, query.uniqueResult());
	    
	    // The query is built and executed.
	    return false;
	  }  
}