org.springframework.data.jpa.repository.JpaReposit接口

JpaReposit是SpringBoot Data JPA提供的非常强大的基础接口。

 

 

可以看出JpaRepository继承了接口PagingAndSortingRepository和QueryByExampleExecutor。而PagingAndSortingRepository又继承CrudRepository。因此，JpaRepository接口同时拥有了基本CRUD功能以及分页功能。

QueryByExampleExecutor又称QBE查询，全称 QueryByExample，即这个是基于数据实例来构建查询的接口 ， 通过传入查询示例来生成查询的SQL的技术， 这里面的一个示例即指一个查询的限制条件。

public interface QueryByExampleExecutor<T> {

    /**
     * Returns a single entity matching the given {@link Example} or {@literal null} if none was found.
     *
     * @param example can be {@literal null}.
     * @return a single entity matching the given {@link Example} or {@literal null} if none was found.
     * @throws org.springframework.dao.IncorrectResultSizeDataAccessException if the Example yields more than one result.
     */
    <S extends T> S findOne(Example<S> example);

    /**
     * Returns all entities matching the given {@link Example}. In case no match could be found an empty {@link Iterable}
     * is returned.
     *
     * @param example can be {@literal null}.
     * @return all entities matching the given {@link Example}.
     */
    <S extends T> Iterable<S> findAll(Example<S> example);

    /**
     * Returns all entities matching the given {@link Example} applying the given {@link Sort}. In case no match could be
     * found an empty {@link Iterable} is returned.
     *
     * @param example can be {@literal null}.
     * @param sort the {@link Sort} specification to sort the results by, must not be {@literal null}.
     * @return all entities matching the given {@link Example}.
     * @since 1.10
     */
    <S extends T> Iterable<S> findAll(Example<S> example, Sort sort);

    /**
     * Returns a {@link Page} of entities matching the given {@link Example}. In case no match could be found, an empty
     * {@link Page} is returned.
     *
     * @param example can be {@literal null}.
     * @param pageable can be {@literal null}.
     * @return a {@link Page} of entities matching the given {@link Example}.
     */
    <S extends T> Page<S> findAll(Example<S> example, Pageable pageable);

    /**
     * Returns the number of instances matching the given {@link Example}.
     *
     * @param example the {@link Example} to count instances for, can be {@literal null}.
     * @return the number of instances matching the {@link Example}.
     */
    <S extends T> long count(Example<S> example);

    /**
     * Checks whether the data store contains elements that match the given {@link Example}.
     *
     * @param example the {@link Example} to use for the existence check, can be {@literal null}.
     * @return {@literal true} if the data store contains elements that match the given {@link Example}.
     */
    <S extends T> boolean exists(Example<S> example);
}

 

当我们需要定义自己的Repository接口的时候，我们可以直接继承JpaRepository，从而获得SpringBoot Data JPA为我们内置的多种基本数据操作方法

/*
 * Copyright 2008-2016 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
 *
 *      http://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;

import java.io.Serializable;
import java.util.List;

import javax.persistence.EntityManager;

import org.springframework.data.domain.Example;
import org.springframework.data.domain.Sort;
import org.springframework.data.repository.NoRepositoryBean;
import org.springframework.data.repository.PagingAndSortingRepository;
import org.springframework.data.repository.query.QueryByExampleExecutor;

/**
 * JPA specific extension of {@link org.springframework.data.repository.Repository}.
 *
 * @author Oliver Gierke
 * @author Christoph Strobl
 * @author Mark Paluch
 */
@NoRepositoryBean
public interface JpaRepository<T, ID extends Serializable>
        extends PagingAndSortingRepository<T, ID>, QueryByExampleExecutor<T> {

    /*
     * (non-Javadoc)
     * @see org.springframework.data.repository.CrudRepository#findAll()
     */
    List<T> findAll();

    /*
     * (non-Javadoc)
     * @see org.springframework.data.repository.PagingAndSortingRepository#findAll(org.springframework.data.domain.Sort)
     */
    List<T> findAll(Sort sort);

    /*
     * (non-Javadoc)
     * @see org.springframework.data.repository.CrudRepository#findAll(java.lang.Iterable)
     */
    List<T> findAll(Iterable<ID> ids);

    /*
     * (non-Javadoc)
     * @see org.springframework.data.repository.CrudRepository#save(java.lang.Iterable)
     */
    <S extends T> List<S> save(Iterable<S> entities);

    /**
     * Flushes all pending changes to the database.
     */
    void flush();

    /**
     * Saves an entity and flushes changes instantly.
     * 
     * @param entity
     * @return the saved entity
     */
    <S extends T> S saveAndFlush(S entity);

    /**
     * Deletes the given entities in a batch which means it will create a single {@link Query}. Assume that we will clear
     * the {@link javax.persistence.EntityManager} after the call.
     * 
     * @param entities
     */
    void deleteInBatch(Iterable<T> entities);

    /**
     * Deletes all entities in a batch call.
     */
    void deleteAllInBatch();

    /**
     * Returns a reference to the entity with the given identifier.
     * 
     * @param id must not be {@literal null}.
     * @return a reference to the entity with the given identifier.
     * @see EntityManager#getReference(Class, Object)
     */
    T getOne(ID id);

    /* (non-Javadoc)
     * @see org.springframework.data.repository.query.QueryByExampleExecutor#findAll(org.springframework.data.domain.Example)
     */
    @Override
    <S extends T> List<S> findAll(Example<S> example);

    /* (non-Javadoc)
     * @see org.springframework.data.repository.query.QueryByExampleExecutor#findAll(org.springframework.data.domain.Example, org.springframework.data.domain.Sort)
     */
    @Override
    <S extends T> List<S> findAll(Example<S> example, Sort sort);

}

 在这里，还有个注意事项，JpaRepository接口的方法是有一定扩展性的，只要方法命名符合一定规范，只要写出方法名就可使用：

  如 findBy[FileldName](String fieldName)