collectionloader.java

来自「hibernate-3.0.5 中文文档」· Java 代码 · 共 201 行

//$Id: CollectionLoader.java,v 1.9 2005/05/19 07:28:57 steveebersole Exp $
package org.hibernate.loader.collection;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.hibernate.FetchMode;
import org.hibernate.HibernateException;
import org.hibernate.LockMode;
import org.hibernate.MappingException;
import org.hibernate.engine.SessionFactoryImplementor;
import org.hibernate.engine.SessionImplementor;
import org.hibernate.loader.OuterJoinLoader;
import org.hibernate.loader.OuterJoinableAssociation;
import org.hibernate.persister.collection.QueryableCollection;
import org.hibernate.sql.JoinFragment;
import org.hibernate.sql.Select;
import org.hibernate.type.AssociationType;
import org.hibernate.type.Type;
import org.hibernate.util.CollectionHelper;
import org.hibernate.util.StringHelper;

/**
 * Loads a collection of values or a many-to-many association.
 * <br>
 * The collection persister must implement <tt>QueryableCOllection<tt>. For
 * other collections, create a customized subclass of <tt>Loader</tt>.
 *
 * @see OneToManyLoader
 * @author Gavin King
 */
public class CollectionLoader extends OuterJoinLoader implements CollectionInitializer {

	private static final Log log = LogFactory.getLog(CollectionLoader.class);

	private final QueryableCollection collectionPersister;

	public CollectionLoader(
			QueryableCollection collectionPersister, 
			SessionFactoryImplementor session, 
			Map enabledFilters)
	throws MappingException {
		this(collectionPersister, 1, session, enabledFilters);
	}

	public CollectionLoader(
			QueryableCollection collectionPersister, 
			int batchSize, 
			SessionFactoryImplementor factory, 
			Map enabledFilters)
	throws MappingException {
		this(collectionPersister, batchSize, null, factory, enabledFilters);
	}
	
	public CollectionLoader(
			QueryableCollection collectionPersister, 
			int batchSize, 
			String subquery, 
			SessionFactoryImplementor factory, 
			Map enabledFilters)
	throws MappingException {

		super(factory, enabledFilters);

		this.collectionPersister = collectionPersister;

		String alias = generateRootAlias( collectionPersister.getRole() );

		final List associations = walkCollectionTree(collectionPersister, alias);

		List allAssociations = new ArrayList();
		allAssociations.addAll(associations);
		allAssociations.add( new OuterJoinableAssociation( 
				collectionPersister.getCollectionType(),
				null, 
				null, 
				alias, 
				JoinFragment.LEFT_OUTER_JOIN, 
				getFactory(), 
				CollectionHelper.EMPTY_MAP 
			) );

		initPersisters(allAssociations, LockMode.NONE);
		initStatementString(alias, associations, batchSize, subquery);

		postInstantiate();

		log.debug( "Static select for collection " + collectionPersister.getRole() + ": " + getSQLString() );
	}

	public void initialize(Serializable id, SessionImplementor session)
	throws HibernateException {
		loadCollection( session, id, getKeyType() );
	}

	private void initStatementString(
		final String alias,
		final List associations,
		final int batchSize,
		final String subquery)
	throws MappingException {

		final int joins = countEntityPersisters( associations );
		final int collectionJoins = countCollectionPersisters( associations ) + 1;

		suffixes = generateSuffixes( joins );
		collectionSuffixes = generateSuffixes( joins, collectionJoins );

		StringBuffer whereString = whereString(alias, collectionPersister.getKeyColumnNames(), batchSize, subquery);
		String filter = collectionPersister.filterFragment( alias, getEnabledFilters() );
		if ( collectionPersister.isManyToMany() ) {
			// from the collection of associations, locate OJA for the
			// ManyToOne corresponding to this persister to fully
			// define the many-to-many; we need that OJA so that we can
			// use its alias here
			// TODO : is there a better way here?
			Iterator itr = associations.iterator();
			AssociationType associationType = ( AssociationType ) collectionPersister.getElementType();
			while ( itr.hasNext() ) {
				OuterJoinableAssociation oja = ( OuterJoinableAssociation ) itr.next();
				if ( oja.getJoinableType() == associationType ) {
					// we found it
					filter += collectionPersister.getManyToManyFilterFragment( oja.getRHSAlias(), getEnabledFilters() );
				}
			}
		}
		whereString.insert( 0, StringHelper.moveAndToBeginning( filter ) );

		JoinFragment ojf = mergeOuterJoins(associations);
		Select select = new Select( getDialect() )
			.setSelectClause(
				collectionPersister.selectFragment(alias, collectionSuffixes[0] ) +
				selectString(associations)
			)
			.setFromClause( collectionPersister.getTableName(), alias )
			.setWhereClause( whereString.toString()	)
			.setOuterJoins(
				ojf.toFromFragmentString(),
				ojf.toWhereFragmentString()
			);

		select.setOrderByClause( orderBy(associations, collectionPersister.getSQLOrderByString(alias) ) );

		if ( getFactory().getSettings().isCommentsEnabled() ) {
			select.setComment( "load collection " + collectionPersister.getRole() );
		}

		sql = select.toStatementString();
	}

	/**
	 * We can use an inner join for first many-to-many association
	 */
	protected int getJoinType(
			AssociationType type, 
			FetchMode config, 
			String path, 
			Set visitedAssociations,
			String lhsTable,
			String[] lhsColumns,
			boolean nullable,
			int currentDepth)
	throws MappingException {

		int joinType = super.getJoinType(
				type, 
				config, 
				path, 
				visitedAssociations, 
				lhsTable, 
				lhsColumns, 
				nullable, 
				currentDepth
		);
		//we can use an inner join for the many-to-many
		if ( joinType==JoinFragment.LEFT_OUTER_JOIN && "".equals(path) ) {
			joinType=JoinFragment.INNER_JOIN;
		}
		return joinType;
	}
	
	protected Type getKeyType() {
		return collectionPersister.getKeyType();
	}

	public String toString() {
		return getClass().getName() + '(' + collectionPersister.getRole() + ')';
	}

	protected boolean isSubselectLoadingEnabled() {
		return hasSubselectLoadableCollections();
	}

}