考虑下面的实体（删除getter和setter以减少代码）-

public class Organization {

  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;

  @OneToMany(fetch = FetchType.LAZY)
  @JoinColumn
  private List<Account> accounts;
}

public class Account {

      @Id
      @GeneratedValue(strategy = GenerationType.IDENTITY)
      private Long id;

      @OneToMany(fetch = FetchType.LAZY)
      @JoinColumn
      private List<Contact> contacts;
    }

public class Contact {

      @Id
      @GeneratedValue(strategy = GenerationType.IDENTITY)
      private Long id;

      @OneToMany(fetch = FetchType.LAZY)
      @JoinColumn
      private List<Certification> certifications;
    }

public class Certification {

      @Id
      @GeneratedValue(strategy = GenerationType.IDENTITY)
      private Long id;

      @OneToMany(fetch = FetchType.LAZY)
      @JoinColumn
      private List<Skill> skills;
    }

public class Skill {

      @Id
      @GeneratedValue(strategy = GenerationType.IDENTITY)
      private Long id;

      private String name;
    }

我使用SpringBootJPA规范来吸引所有拥有技能认证（比如java）的组织

public static Specification<Organization> getPartner() {
        return (root, cq, cb) -> {

              Join<Organization, Skill> skillJoin = root.join("accounts").join("contacts")
                  .join("certifications").join("skills");
              return cb.equal(skillJoin.get("name"), "java");
        }
    }

上面的代码需要8-9秒才能返回结果。可能是由于多个@onetomany连接。对性能改进有何建议：）