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Spring Data module for JPA repositories.
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package org.springframework.data.jpa.repository.support;

import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Optional;

import javax.persistence.EntityManager;

import org.springframework.data.jpa.repository.EntityGraph;
import org.springframework.data.jpa.repository.query.Jpa21Utils;
import org.springframework.data.jpa.repository.query.JpaEntityGraph;
import org.springframework.data.util.Optionals;
import org.springframework.util.Assert;

/**
 * Default implementation of {@link QueryHints}.
 *
 * @author Christoph Strobl
 * @author Oliver Gierke
 * @since 2.0
 */
class DefaultQueryHints implements QueryHints {

	private final JpaEntityInformation information;
	private final CrudMethodMetadata metadata;
	private final Optional entityManager;

	/**
	 * Creates a new {@link DefaultQueryHints} instance for the given {@link JpaEntityInformation},
	 * {@link CrudMethodMetadata}, {@link EntityManager} and whether to include fetch graphs.
	 *
	 * @param information must not be {@literal null}.
	 * @param metadata must not be {@literal null}.
	 * @param entityManager must not be {@literal null}.
	 */
	private DefaultQueryHints(JpaEntityInformation information, CrudMethodMetadata metadata,
			Optional entityManager) {

		this.information = information;
		this.metadata = metadata;
		this.entityManager = entityManager;
	}

	/**
	 * Creates a new {@link QueryHints} instance for the given {@link JpaEntityInformation}, {@link CrudMethodMetadata}
	 * and {@link EntityManager}.
	 *
	 * @param information must not be {@literal null}.
	 * @param metadata must not be {@literal null}.
	 * @return
	 */
	public static QueryHints of(JpaEntityInformation information, CrudMethodMetadata metadata) {

		Assert.notNull(information, "JpaEntityInformation must not be null!");
		Assert.notNull(metadata, "CrudMethodMetadata must not be null!");

		return new DefaultQueryHints(information, metadata, Optional.empty());
	}

	/*
	 * (non-Javadoc)
	 * @see org.springframework.data.jpa.repository.support.QueryHints#withFetchGraphs()
	 */
	@Override
	public QueryHints withFetchGraphs(EntityManager em) {
		return new DefaultQueryHints(this.information, this.metadata, Optional.of(em));
	}

	/*
	 * (non-Javadoc)
	 * @see java.lang.Iterable#iterator()
	 */
	@Override
	public Iterator> iterator() {
		return asMap().entrySet().iterator();
	}

	/*
	 * (non-Javadoc)
	 * @see org.springframework.data.jpa.repository.support.QueryHints#asMap()
	 */
	@Override
	public Map asMap() {

		Map hints = new HashMap<>();

		hints.putAll(metadata.getQueryHints());
		hints.putAll(getFetchGraphs());

		return hints;
	}

	private Map getFetchGraphs() {

		return Optionals
				.mapIfAllPresent(entityManager, metadata.getEntityGraph(),
						(em, graph) -> Jpa21Utils.tryGetFetchGraphHints(em, getEntityGraph(graph), information.getJavaType()))
				.orElse(Collections.emptyMap());
	}

	private JpaEntityGraph getEntityGraph(EntityGraph entityGraph) {

		String fallbackName = information.getEntityName() + "." + metadata.getMethod().getName();
		return new JpaEntityGraph(entityGraph, fallbackName);
	}
}