[hibernate-issues] [Hibernate-JIRA] Created: (HSHARDS-9) Add ShardAware interface and related exit strategy logic

[Nathan Silberman (JIRA)]

Add ShardAware interface and related exit strategy logic
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                 Key: HSHARDS-9
                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HSHARDS-9
             Project: Hibernate Shards
          Issue Type: New Feature
          Components: strategy
    Affects Versions: 3.0.0.Beta1
         Environment: Hibernate 3.2, Database: DB2
            Reporter: Nathan Silberman
            Assignee: Max Ross


Domain model awareness of its host Shard. Any domain model that implemented a 'ShardAware' interface would contain a Set<ShardId> that could be injected by the relevant ExitStrategy.

This could be solved by adding the following interface:

-------------------------------------------------------

package org.hibernate.shards;

import org.hibernate.shards.ShardId;

import java.util.Set;

/**
 * Interface for persistent objects that are aware of the virtual shardIds
 * that host them.
 */
public interface ShardAware {
	
	/**
	 * Sets the virtual ShardIds that host the implementing
	 * persistant object
	 * 
	 * @param shardid
	 * 			a non-null, non-empty Set of ShardIds
         * @throws IllegalArgumentException
         *                      if <tt>shardIds</tt> is null or empty
	 */
	void setShardIds( Set<ShardId> shardids );
}

---------------------------------------------------


An simple exit strategy that could be used, for example, would set the ShardIds for each resulting ShardAware domain model: 


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package org.hibernate.shards.strategy.exit;

import java.util.List;

import org.hibernate.shards.Shard;
import org.hibernate.shards.ShardAware;

/**
 * ShardAwareConcatenateListsExistStrategy sets the ShardIds on each of the given 
 * objects returned by each Shard. 
 * 
 * One should be aware that usage of this class adds O(n) overhead to each retrieval
 * as the setting of each ShardIds Set is invoked by iterating over the entire resultSet.
 */
public class ShardAwareConcatenateListsExistStrategy extends ConcatenateListsExitStrategy {

	@Override
	public synchronized boolean addResult(List<Object> oneResult, Shard shard ) {
		
		if ( oneResult != null && ! oneResult.isEmpty()
				&& oneResult.get( 0 ) instanceof ShardAware ) {
			
			for( Object object : oneResult ) {
				((ShardAware)object).setShardIds( shard.getShardIds() );
			}
		}
		
		return super.addResult( oneResult, shard );
	}
}
---------------------------------------

This change might require changes wherever ShardAccessStrategy.apply() could be invoked.

I have made the changes including a small alteration to the ShardedCriteriaImpl, to use ShardAwareConcatenateListsExistStrategy  instead of ConcatenateListsExitStrategy, with success. 

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