spring-data-jpa QueryHints 源码

spring-data-jpa QueryHints 代码

文件路径：/spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/support/QueryHints.java

/*
 * Copyright 2017-2022 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.springframework.data.jpa.repository.support;

import java.util.function.BiConsumer;

import jakarta.persistence.EntityManager;

import org.springframework.util.Assert;

/**
 * QueryHints provides access to query hints defined via {@link CrudMethodMetadata#getQueryHints()} QueryHintList()} by
 * default excluding JPA {@link jakarta.persistence.EntityGraph}. The object allows to switch between query hints for
 * count queries with or without fetch graph hints.
 *
 * @author Christoph Strobl
 * @author Oliver Gierke
 * @author Jens Schauder
 * @since 2.0
 */
public interface QueryHints {

	/**
	 * Create a new {@link QueryHints} object from the given {@code sources}.
	 *
	 * @param sources must not be {@literal null}.
	 * @return a merged representation of {@link QueryHints QueryHints}.
	 * @since 2.4
	 */
	static QueryHints from(QueryHints... sources) {

		Assert.notNull(sources, "Sources must not be null");

		MutableQueryHints result = new MutableQueryHints();

		for (QueryHints queryHints : sources) {
			queryHints.forEach(result.getValues()::add);
		}

		return result;
	}

	/**
	 * Creates and returns a new {@link QueryHints} instance including {@link jakarta.persistence.EntityGraph}.
	 *
	 * @param em must not be {@literal null}.
	 * @return new instance of {@link QueryHints}.
	 */
	QueryHints withFetchGraphs(EntityManager em);

	/**
	 * Creates and returns a new {@link QueryHints} instance that will contain only those hints applicable for count
	 * queries.
	 *
	 * @return new instance of {@link QueryHints}.
	 * @since 2.2
	 */
	QueryHints forCounts();

	/**
	 * Performs the given action for each element of this query hints object until all hints have been processed or the
	 * action throws an exception. Actions are performed in the order of iteration, if that order is specified. Exceptions
	 * thrown by the action are relayed to the caller.
	 * <p>
	 * Passes each query hint to the consumer. Query hint keys might appear more than once.
	 *
	 * @param action to process query hints consisting of a key and a value.
	 * @since 2.4
	 */
	void forEach(BiConsumer<String, Object> action);

	/**
	 * Null object implementation of {@link QueryHints}.
	 *
	 * @author Oliver Gierke
	 * @since 2.0
	 */
	enum NoHints implements QueryHints {

		INSTANCE;

		@Override
		public QueryHints withFetchGraphs(EntityManager em) {
			return this;
		}

		@Override
		public QueryHints forCounts() {
			return this;
		}

		@Override
		public void forEach(BiConsumer<String, Object> action) {}
	}
}

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