Spring Data JPA投影从DB中选择的字段

Question

我正在测试Spring Data 1.10.4.Release，遵循Spring Data Docs http://Docs.Spring.io/spring-data/jpa/Docs/current/reference/html/#Projections中的示例

@Entity
public class Person {

  @Id @GeneratedValue
  private Long id;
  private String firstName, lastName;

  @OneToOne
  private Address address;
}

@Entity
public class Address {

  @Id @GeneratedValue
  private Long id;
  private String street, state, country;
}

• 问题1:

以下预测：

interface PersonLimited {  

  String getFirstName(); 

  AddressLimited getAddress();
}

interface AddressLimited {  

  String getCountry(); 
}

当我运行findPersonByFirstNameProjectedForLimitedData时

interface PersonRepository extends CrudRepository<Person, Long> {

  @Query("select p from Person p where p.firstName = ?1")
  PersonLimited findPersonByFirstNameProjectedForLimitedData(String firstName);
}

{
    firstName: 'Homer',
    address: {
        country: 'USA'
    }
}

SELECT person0_.firstName      AS col_0_0_, 
       address1_.id            AS id1_13_, 
       address1_.street        AS street2_13_, 
       address1_.state         AS state3_13_, 
       address1_.country       AS country4_13_
FROM   person person0_ 
       LEFT OUTER JOIN address address1_ 
                    ON person0_.addressId = address1_.id 
WHERE  person0_.firstName = ?  

SELECT person0_.firstName      AS col_0_0_, 
       address1_.country       AS country4_13_
FROM   person person0_ 
       LEFT OUTER JOIN address address1_ 
                    ON person0_.addressId = address1_.id 
WHERE  person0_.firstName = ?  

• 问题2:

对于与上述相同的预测,

当我运行findAllPersonsProjectedForLimitedData时

interface PersonRepository extends CrudRepository<Person, Long> {

  @Query("select p from Person p")
  List<PersonLimited> findAllPersonsProjectedForLimitedData();
}

[
     {
        firstName: 'Homer',
        address: {
            country: 'USA'
        }
     },
     {
        firstName: 'Maggie',
        address: {
            country: 'USA'
        }
     }
]

SELECT person0_.id                 AS id1_18_, 
       person0_.firstName          AS firstName2_18_, 
       person0_.lastName           AS lastName3_18_, 
       person0_.addressid          AS company4_18_
FROM   person person0_ 

SELECT address0_.id         AS id1_13_0_, 
       address0_.street     AS street2_13_0_, 
       address0_.state      AS state3_13_0_, 
       address0_.country    AS country4_13_0_
FROM   address address0_ 
WHERE  address0_.id = ? 

SELECT person0_.firstName        AS firstName2_18_
FROM   person person0_ 

SELECT address0_.country    AS country4_13_0_
FROM   address address0_ 
WHERE  address0_.id = ? 

Answer 1

如果您希望在Spring数据投影中使用注释@Query，那么您必须使用字段别名，并且您需要确保对与投影字段匹配的项目进行别名。下面的代码应该适用于问题1：

interface PersonRepository extends CrudRepository<Person, Long> {

  @Query("select p.firstName as firstname, p.address as address from Person p where p.firstName = ?1")
  PersonLimited findPersonByFirstNameProjectedForLimitedData(String firstName);
}

您可以使用的另一种选择是使用属性表达式定义查询。只要可能：

interface PersonRepository extends CrudRepository<Person, Long> {

  List<PersonLimited> findByFirstName(String firstName);
}