java - 在联合表上使用 Specifications 和 CriteriaQuery 的 Spring JPA

Question

我正在使用 JPA 规范和 CriteriaQuery 以便将 where 子句添加到我的实体中。

域类:

public class Domain {

  @Id
  @Column(name = "id")
  @GeneratedValue(strategy = GenerationType.AUTO)
  private Long id;

  @Column(name = "account_id")
  private Long accountId;

  @OneToMany(cascade = CascadeType.ALL)
  @JoinColumn(name = "domain_id")
  private List<Notification> notification;
}

通知类:

public class Notification {

  @Id
  @Column(name = "id")
  @GeneratedValue(strategy = GenerationType.AUTO)
  private Long id;

  @Column(name = "domain_id")
  private Long domainId;

  @Column(name = "contact")
  private String contact;
}

然后我有以下用于创建规范的类:

public class DomainSpecification implements Specification<Domain> {

  final private SearchCriteria criteria;

  public DomainSpecification(SearchCriteria searchCriteria) {
    this.criteria = searchCriteria;
  }

  @Override
  public Predicate toPredicate(
          Root<Domain> root, CriteriaQuery<?> query, CriteriaBuilder builder) {

     switch (criteria.getOperation()) {
      case ":":
        if (root.get(criteria.getKey()).getJavaType() == String.class) {
          return builder.like(
                  root.<String>get(criteria.getKey()),
                  "%" + criteria.getValue() + "%");
        } else {
          return builder.equal(root.get(criteria.getKey()),
                  criteria.getValue());
        }
      case "=":
        return builder.equal(root.get(criteria.getKey()),
                criteria.getValue());
      default:
        return null;
    }
  }

}

和 SearchCriteria 对象:

public class SearchCriteria {

  private final String key;
  private final String operation;
  private final Object value;

  public SearchCriteria(String key, String operation, Object value) {
    this.key = key;
    this.operation = operation;
    this.value = value;
  }

  public String getKey() {
    return key;
  }

  public String getOperation() {
    return operation;
  }

  public Object getValue() {
    return value;
  }

}

然后，每当我想创建一个 where 子句时，我都会执行以下操作:

DomainSpecification idSpecification
        = new DomainSpecification(
                new SearchCriteria("id", "=", domainId));

Specifications<Domain> specifications = Specifications.where(idSpecification);

final Domain domain = this.domainRepository.findOne(specifications);

这将通过域实体中名为 id 的字段进行搜索。

现在，我还可以如何按我要加入的实体进行过滤？例如，我想过滤 where Domain.id = 10 and Notification.contact = "abc"?

谢谢你的帮助

Answer 1

您可以将您的Specification定义包装到辅助类中:

public class DelegationSpecificationsHelper {

    public static Specification<Domain> notificationContactSpec(String contact) {
        return (root, query, cb) -> cb.equal(root.join("notification").get("contact"), contact);
    }

    public static Specification<Domain> idSpec(SearchCriteria searchCriteria) {
        switch (criteria.getOperation()) {
          case ":":
            if (root.get(criteria.getKey()).getJavaType() == String.class) {
              return builder.like(
                      root.<String>get(criteria.getKey()),
                      "%" + criteria.getValue() + "%");
            } else {
              return builder.equal(root.get(criteria.getKey()),
                      criteria.getValue());
            }
          case "=":
            return builder.equal(root.get(criteria.getKey()),
                    criteria.getValue());
          default:
            return null;
        }
    }
}

然后你可以像这样使用它:

Specifications<Domain> specifications = Specifications.where(DelegationSpecificationsHelper.idSpec(new SearchCriteria("id", "=", domainId))
                                                      .and(DelegationSpecificationsHelper.notificationContactSpec("someSearchString"));

静态导入和一些重构之后:

SearchCriteria idCriteria = new SearchCriteria("id", "=", domainId)
Specifications<Domain> specifications = 
                 Specifications.where(idSpec(idCriteria)
                               .and(notificationContactSpec("someSearchString"));

当然你应该从这里摆脱硬编码值:cb.equal(root.join("notification").get("contact"), contact); 并改用一些 DTO 对象或生成的 JPA 元模型。

添加元模型后它看起来像这样:

 public static Specification<Domain> notificationContactSpec(String contactValue) {
        return (root, query, cb) -> cb.equal(root.join(Domain_.notification).get(Notification_.contact), contactValue);
 }

有关元模型生成的更多信息: https://docs.jboss.org/hibernate/orm/5.0/topical/html/metamodelgen/MetamodelGenerator.html