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Hibernate's core ORM functionality
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/*
 * Hibernate, Relational Persistence for Idiomatic Java
 *
 * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
 * See the lgpl.txt file in the root directory or .
 */
package org.hibernate.loader.collection;

import org.hibernate.engine.spi.LoadQueryInfluencers;
import org.hibernate.engine.spi.SessionFactoryImplementor;
import org.hibernate.persister.collection.QueryableCollection;

/**
 * Contract for building {@link CollectionInitializer} instances capable of performing batch-fetch loading.
 *
 * @author Steve Ebersole
 *
 * @see org.hibernate.loader.BatchFetchStyle
 */
public abstract class BatchingCollectionInitializerBuilder {
	public static BatchingCollectionInitializerBuilder getBuilder(SessionFactoryImplementor factory) {
		switch ( factory.getSettings().getBatchFetchStyle() ) {
			case PADDED: {
				return PaddedBatchingCollectionInitializerBuilder.INSTANCE;
			}
			case DYNAMIC: {
				return DynamicBatchingCollectionInitializerBuilder.INSTANCE;
			}
			default: {
				return org.hibernate.loader.collection.plan.LegacyBatchingCollectionInitializerBuilder.INSTANCE;
				//return LegacyBatchingCollectionInitializerBuilder.INSTANCE;
			}
		}
	}

	/**
	 * Builds a batch-fetch capable CollectionInitializer for basic and many-to-many collections (collections with
	 * a dedicated collection table).
	 *
	 * @param persister THe collection persister
	 * @param maxBatchSize The maximum number of keys to batch-fetch together
	 * @param factory The SessionFactory
	 * @param influencers Any influencers that should affect the built query
	 *
	 * @return The batch-fetch capable collection initializer
	 */
	public CollectionInitializer createBatchingCollectionInitializer(
			QueryableCollection persister,
			int maxBatchSize,
			SessionFactoryImplementor factory,
			LoadQueryInfluencers influencers) {
		if ( maxBatchSize <= 1 ) {
			// no batching
			return buildNonBatchingLoader( persister, factory, influencers );
		}

		return createRealBatchingCollectionInitializer( persister, maxBatchSize, factory, influencers );
	}

	protected abstract CollectionInitializer createRealBatchingCollectionInitializer(
			QueryableCollection persister,
			int maxBatchSize,
			SessionFactoryImplementor factory,
			LoadQueryInfluencers influencers);


	/**
	 * Builds a batch-fetch capable CollectionInitializer for one-to-many collections (collections without
	 * a dedicated collection table).
	 *
	 * @param persister THe collection persister
	 * @param maxBatchSize The maximum number of keys to batch-fetch together
	 * @param factory The SessionFactory
	 * @param influencers Any influencers that should affect the built query
	 *
	 * @return The batch-fetch capable collection initializer
	 */
	public CollectionInitializer createBatchingOneToManyInitializer(
			QueryableCollection persister,
			int maxBatchSize,
			SessionFactoryImplementor factory,
			LoadQueryInfluencers influencers) {
		if ( maxBatchSize <= 1 ) {
			// no batching
			return buildNonBatchingLoader( persister, factory, influencers );
		}

		return createRealBatchingOneToManyInitializer( persister, maxBatchSize, factory, influencers );
	}

	protected abstract CollectionInitializer createRealBatchingOneToManyInitializer(
			QueryableCollection persister,
			int maxBatchSize,
			SessionFactoryImplementor factory,
			LoadQueryInfluencers influencers);

	protected CollectionInitializer buildNonBatchingLoader(
			QueryableCollection persister,
			SessionFactoryImplementor factory,
			LoadQueryInfluencers influencers) {
		return persister.isOneToMany() ?
				new OneToManyLoader( persister, factory, influencers ) :
				new BasicCollectionLoader( persister, factory, influencers );
	}
}