我有一个User实体，一个UserToApplication实体和一个Application实体。
单个User可以访问多个Application。单个Application可以被多个User使用。
这是User实体。
@Entity
@Table(name = "USER", schema = "UDB")
public class User {
private Long userId;
private Collection<Application> applications;
private String firstNm;
private String lastNm;
private String email;
@SequenceGenerator(name = "generator", sequenceName = "UDB.USER_SEQ", initialValue = 1, allocationSize = 1)
@Id
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "generator")
@Column(name = "USER_ID", unique = true, nullable = false)
public Long getUserId() {
return userId;
}
public void setUserId(Long userId) {
this.userId = userId;
}
@OneToMany(mappedBy = "user", fetch = FetchType.LAZY)
public Collection<Application> getApplications() {
return applications;
}
public void setApplications(Collection<Application> applications) {
this.applications = applications;
}
/* Other getters and setters omitted for brevity */
}
这是UserToApplication实体。
@Entity
@Table(name = "USER_TO_APPLICATION", schema = "UDB")
public class Application {
private Long userToApplicationId;
private User user;
private Application application;
@SequenceGenerator(name = "generator", sequenceName = "UDB.USER_TO_APP_SEQ", initialValue = 0, allocationSize = 1)
@Id
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "generator")
@Column(name = "USER_TO_APPLICATION_ID", unique = true, nullable = false)
public Long getUserToApplicationId() {
return userToApplicationId;
}
public void setUserToApplicationId(Long userToApplicationId) {
this.userToApplicationId = userToApplicationId;
}
@ManyToOne
@JoinColumn(name = "USER_ID", referencedColumnName = "USER_ID", nullable = false)
public User getUser() {
return user;
}
public void setUser(User user) {
this.user = user;
}
@ManyToOne
@JoinColumn(name = "APPLICATION_ID", nullable = false)
public Application getApplication() {
return application;
}
}
这是Application实体。
@Entity
@Table(name = "APPLICATION", schema = "UDB")
public class Application {
private Long applicationId;
private String name;
private String code;
/* Getters and setters omitted for brevity */
}
我有以下Specification，我用来搜索User，firstNm和lastNm的email。
public class UserSpecification {
public static Specification<User> findByFirstNmLastNmEmail(String firstNm, String lastNm, String email) {
return new Specification<User>() {
@Override
public Predicate toPredicate(Root<User> root, CriteriaQuery<?> query, CriteriaBuilder cb) {
final Predicate firstNmPredicate = null;
final Predicate lastNmPredicate = null;
final Predicate emailPredicate = null;
if (!StringUtils.isEmpty(firstNm)) {
firstNmPredicate = cb.like(cb.lower(root.get(User_.firstNm), firstNm));
}
if (!StringUtils.isEmpty(lastNm)) {
lastNmPredicate = cb.like(cb.lower(root.get(User_.lastNm), lastNm));
}
if (!StringUtils.isEmpty(email)) {
emailPredicate = cb.like(cb.lower(root.get(User_.email), email));
}
return cb.and(firstNmPredicate, lastNmPredicate, emailPredicate);
}
};
}
}
这是我到目前为止的User_元模型。
@StaticMetamodel(User.class)
public class User_ {
public static volatile SingularAttribute<User, String> firstNm;
public static volatile SingularAttribute<User, String> lastNm;
public static volatile SingularAttribute<User, String> email;
}
现在，我想将一个应用程序ID列表传递给Specification，这样它的方法签名就是：
public static Specification<User> findByFirstNmLastNmEmailApp(String firstNm, String lastNm, String email, Collection<Long> appIds)
所以，我的问题是，我可以将@OneToMany映射添加到我的User_实体的Collection<Application> applications字段的User元模型中，然后我将如何在Specification中引用它？
我当前的Specification将类似于以下SQL查询：
select * from user u
where lower(first_nm) like '%firstNm%'
and lower(last_nm) like '%lastNm%'
and lower(email) like '%email%';
我想在新的Specification中实现的是这样的：
select * from user u
join user_to_application uta on uta.user_id = u.user_id
where lower(u.first_nm) like '%firstNm%'
and lower(u.last_nm) like '%lastNm%'
and lower(u.email) like '%email%'
and uta.application_id in (appIds);
是否有可能在元模型中进行这种映射，我怎么能在我的Specification中实现这个结果？
我找到了解决方案。要映射一个到多个属性，在元模型中我添加了以下内容：
public static volatile CollectionAttribute<User, Application> applications;
我还需要为Application实体添加元模型。
@StaticMetamodel(Application.class)
public class Application_ {
public static volatile SingularAttribute<Application, Long> applicationId;
}
然后在我的Specification中，我可以使用applications实例上的.join()方法为用户访问Root<User>。这是我组建的Predicate。
final Predicate appPredicate = root.join(User_.applications).get(Application_.applicationId).in(appIds);
此外，值得注意的是，如果任何输入值为空，我在问题中写的Specification将不起作用。传递给Predicate的.and()方法的null CriteriaBuilder将导致NullPointerException。所以，我创建了一个ArrayList类型的Predicate，然后如果相应的参数非空，则将每个Predicate添加到列表中。最后，我将ArrayList转换为数组，将其传递给.and()的CriteriaBuilder函数。这是最后的Specification：
public class UserSpecification {
public static Specification<User> findByFirstNmLastNmEmailApp(String firstNm, String lastNm, String email, Collection<Long> appIds) {
return new Specification<User>() {
@Override
public Predicate toPredicate(Root<User> root, CriteriaQuery<?> query, CriteriaBuilder cb) {
final Collection<Predicate> predicates = new ArrayList<>();
if (!StringUtils.isEmpty(firstNm)) {
final Predicate firstNmPredicate = cb.like(cb.lower(root.get(User_.firstNm), firstNm));
predicates.add(firstNmPredicate);
}
if (!StringUtils.isEmpty(lastNm)) {
final Predicate lastNmPredicate = cb.like(cb.lower(root.get(User_.lastNm), lastNm));
predicates.add(lastNmPredicate);
}
if (!StringUtils.isEmpty(email)) {
final Predicate emailPredicate = cb.like(cb.lower(root.get(User_.email), email));
predicates.add(emailPredicate);
}
if (!appIds.isEmpty()) {
final Predicate appPredicate = root.join(User_.applications).get(Application_.applicationId).in(appIds);
predicates.add(appPredicate);
}
return cb.and(predicates.toArray(new Predicate[predicates.size()]));
}
};
}
}