CayenneUtils.java

package strimillinn.core;

import java.util.List;

import org.apache.cayenne.DataObject;
import org.apache.cayenne.DataRow;
import org.apache.cayenne.ObjectContext;
import org.apache.cayenne.exp.Property;
import org.apache.cayenne.map.ObjEntity;
import org.apache.cayenne.query.SQLTemplate;

public class CayenneUtils {

	/**
	 * @return DataRows containing distinct values of the given properties in the given entity.
	 * 
	 * @param oc The ObjectContext to fetch into
	 * @param entityClass Class of Cayenne entity to fetch
	 * @param properties List of properties to fetch values for
	 */
	public static List<DataRow> distinctValues( ObjectContext oc, Class<? extends DataObject> entityClass, Property<?>... properties ) {
		String sqlString = sqlStringForDistinctSelect( oc, entityClass, properties );
		SQLTemplate query = new SQLTemplate( entityClass, sqlString );
		query.setFetchingDataRows( true );
		return oc.performQuery( query );
	}

	/**
	 * @return SQL string to fetch distinct values of [properties] in the given entity.
	 * 
	 * @param oc The ObjectContext user to resolve the class to an entity.
	 * @param entityClass Class of Cayenne entity to fetch
	 * @param properties List of properties to fetch values for
	 */
	static String sqlStringForDistinctSelect( ObjectContext oc, Class<? extends DataObject> entityClass, Property<?>... properties ) {
		ObjEntity entity = oc.getEntityResolver().getObjEntity( entityClass );
		String dbEntityName = entity.getDbEntityName();

		StringBuilder b = new StringBuilder();
		b.append( "select distinct " );

		for( int i = 0; i < properties.length; i++ ) {
			if( i > 0 ) {
				b.append( "," );
			}

			String attributeName = properties[i].getName();
			String dbAttributeName = entity.getAttribute( attributeName ).getDbAttributeName();
			b.append( dbAttributeName );
		}

		b.append( " from " );
		b.append( dbEntityName );

		String sqlString = b.toString();
		return sqlString;
	}
}