JPA查询之Specification以及HQL、SQL查询

1、Specification

//查询条件List
List<Predicate> predicateList = new ArrayList<Predicate>();
 
Specification specification = new Specification() {
    @Override
    public Predicate toPredicate(Root root, CriteriaQuery criteriaQuery, CriteriaBuilder criteriaBuilder) {
        //root即是Join<>内部第一个泛型的类型，意思就是用SkuProduct与Picture通过SkuProduct的pictures左联
        Join<SkuProduct,Picture> skuProductPictureJoin = root.join("pictures",JoinType.INNER);
        //添加第1个查询条件：SkuProduct的code等于skuProduct.getCode()，然后将这个criteriaBuilder的条件添加到predicateList
        predicateList.add(criteriaBuilder.equal(root.get("code"),skuProduct.getCode()));
        //添加第2个条件
        predicateList.add(criteriaBuilder.notEqual(skuProductPictureJoin.get("pictureType"),0));
        //返回
        return criteriaBuilder.and(predicateList.toArray(new Predicate[predicateList.size()]));
    }
};
 
//重要说明：Specification不支持右连接！
//Specification specification = new Specification() {
//    @Override
//    public Predicate toPredicate(Root root, CriteriaQuery criteriaQuery, CriteriaBuilder criteriaBuilder) {
//        Join<Picture,SkuProduct> skuProductPictureJoin = root.join("pictures",JoinType.RIGHT);
//        predicateList.add(criteriaBuilder.notEqual(root.get("pictureType"),0));
//        predicateList.add(criteriaBuilder.equal(skuProductPictureJoin.get("code"),skuProduct.getCode()));
//        return criteriaBuilder.and(predicateList.toArray(new Predicate[predicateList.size()]));
//    }
//};
 
List<SkuProduct> results = skuProductRepository.findAll(specification);
if(results!=null){
    results.stream().forEach(result->{
        System.out.println(result);
    });
}

2、HQL

@Query(value = "SELECT p FROM Picture p WHERE p.code= :code")
    List<Picture> findByPicture(@Param(value = "code") String code);

3、SQL

3.1--:占位符

@Query(value = "SELECT p.* FROM picture p LEFT JOIN sku_product_pictures sp_p ON p.id=sp_p.pictures_id LEFT JOIN sku_product sp ON sp_p.sku_product_id=sp.id WHERE sp.code= :code AND p.picture_type=0",nativeQuery = true)
    List<Picture> findBySkuProductCodeAndPicture(@Param(value = "code") String code);

3.2--?占位符

@Query(value = "SELECT p.* FROM picture p LEFT JOIN sku_product_pictures sp_p ON p.id=sp_p.pictures_id LEFT JOIN sku_product sp ON sp_p.sku_product_id=sp.id WHERE sp.code=?1 AND p.picture_type=?2",nativeQuery = true)
    List<Picture> findSkuProductCodeAndPicture(String code,int pictureType);

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原文地址：https://blog.csdn.net/trusause/article/details/78672595