2020-11-12

jpa 在没有建立关联映射关系的情况下做关联查询 jpa join query without association

@Override
    public Specification<A> toSpecification() {
        return new Specification<DicMedInfo>() {
            @Override
            public Predicate toPredicate(Root<A> root, CriteriaQuery<?> criteriaQuery,
                                         CriteriaBuilder criteriaBuilder) {
                

                Root<B> bRoot = criteriaQuery.from(B.class);

                Predicate predicateJoin = criteriaBuilder.equal(root.get("id"), bRoot.get("aId"));
                Predicate predicateCond = criteriaBuilder.equal(bRoot.get("bId"), categoryId);

                Predicate finalPredic = criteriaBuilder.and(predicateJoin, predicateCond);

                return finalPredic;
            }
        };
    }