Spring Data JPA Projection从DB中选择了字段

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

我注意到一些问题，我有两个问题。

首先让我假设我有这两个实体：

@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：

对于以下预测：

 interface PersonLimited { String getFirstName(); AddressLimited getAddress(); } interface AddressLimited { String getCountry(); } 

当我运行findPersonByFirstNameProjectedForLimitedData时

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

它完全返回预期的结果：

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

现在，如果我查看生成的SQL，这就是我所拥有的：

 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 = ? 

“Person”实体的投影仅选择“fistName”，这是100％正确的，因为在PersonLimited接口中我只定义了“getFirstName”。

但对于“地址”实体，它选择所有字段，这是错误的，因为在AddressLimited接口中我只定义了“getCountry”，它应该只选择“country”。

生成的查询应该类似于：

 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 = ? 

所以问题是，为什么不选择地址“实体”的“国家/地区”字段？ 为什么需要选择所有字段？ 这是spring的一个错误吗？

• 问题2：

对于与上述相同的投影，

当我运行findAllPersonsProjectedForLimitedData时

 interface PersonRepository extends CrudRepository { @Query("select p from Person p") List findAllPersonsProjectedForLimitedData(); } 

它完全返回预期的结果：

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

现在，如果我查看生成的SQL，这就是我所拥有的：

 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 = ? 

在这里，Person和Address实体的投影是选择所有错误的字段，它应该只选择“firstName”和“country”。

生成的查询应该类似于：

 SELECT person0_.firstName AS firstName2_18_ FROM person person0_ SELECT address0_.country AS country4_13_0_ FROM address address0_ WHERE address0_.id = ? 

这是正常的行为，不应该只选择我们需要的字段吗？

谢谢，

Answer 1

如果要使用带有Spring Data Projections的注释@Query ，则必须使用字段别名，并且需要确保对与投影字段匹配的项目进行别名。 以下代码适用于问题1：

 interface PersonRepository extends CrudRepository { @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方法是使用Property Expressions定义查询。 只要可能：

 interface PersonRepository extends CrudRepository { List findByFirstName(String firstName); }