为什么在 JPA 中通过连接两个不相关的实体来获取数据时没有设置投影字段?

Question

我正在尝试通过连接两个不相关的实体来使用投影获取一些特定的列值。但我没有得到任何价值。 存储库代码是：-

@Repository
public interface PersonRepository extends CrudRepository<Person, Long> {
@Query("SELECT p.id,p.firstName,p.lastName,a.city FROM Person p INNER JOIN Address a on p.id = a.personId")
public List<PersonAndAddressSummary> findAllPersonSummary();
}

人员类

@Entity
public class Person {
@Id
private long id;
private String firstName;
private String lastName;
private long phone;
public long getId() {
return id;
}
public void setId(long id) {
this.id = id;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public long getPhone() {
return phone;
}
public void setPhone(long phone) {
this.phone = phone;
}
}

Address class
@Entity
public class Address {
@Id
private int id;
private String street;
private String state;
private int personId;
private String country;
private int houseNo;
private String city;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getStreet() {
return street;
}
public void setStreet(String street) {
this.street = street;
}
public String getState() {
return state;
}
public void setState(String state) {
this.state = state;
}
public int getPersonId() {
return personId;
}
public void setPersonId(int personId) {
this.personId = personId;
}
public String getCountry() {
return country;
}
public void setCountry(String country) {
this.country = country;
}
public int getHouseNo() {
return houseNo;
}
public void setHouseNo(int houseNo) {
this.houseNo = houseNo;
}
public String getCity() {
return city;
}
public void setCity(String city) {
this.city = city;
}
}

投影接口

public interface PersonAndAddressSummary {
public String getId();
public String getFirstName();
public String getLastName();
public String getCity();
}

执行此 Spring 启动应用程序后，我得到的输出是这样的。

[{"lastName":null,"firstName":null,"city":null,"id":null},{"lastName":null,"firstName":null,"city":null,"id":null},{"lastName":null,"firstName":null,"city":null,"id":null}]

尽管有可用的记录与地址类中的每个人完全匹配(人员和地址表中可用的数据(。

Answer 1

如果两个实体之间没有联接，则无法获取其他实体的数据。每个存储库在 jpa 中都是特定于类的。您必须为每个类定义不同的投影。

@Repository
public interface PersonRepository extends CrudRepository<Person, Long> {
@Query("SELECT p FROM Person p")
public List<PersonAndSummary> findAllPersonSummary();
}

@Repository
public interface AddressRepository extends CrudRepository<Address, Long> {
@Query("SELECT a FROM Address a where a.personId=:personId")
public AddressSummary findAddressSummary(@Param("personId") int personId);
}

public interface PersonSummary {
public String getId();
public String getFirstName();
public String getLastName();
}

public interface AddressSummary {
public String getCity();
}

public interface PersonAndAddressSummary extends PersonSummary, AddressSummary{
}

现在在您的服务类中查找人员摘要列表。现在迭代此列表并按 personId 获取地址摘要。

List<PersonSummary> personSummaryList = yourRepositoryName.findAllPersonSummary();
List<PersonAndAddressSummary> list = new ArrayList<>();
for(PersonSummary summary: personSummaryList){
AddressSummary addressSummary = repositoryName.findAddressSummary(summary.getId());
//now add required fields in your list
}