如何使用Spring Boot从自定义查询返回包含少量字段的自定义列表？

Question

I'm developing a REST web service with Spring Boot 2 and Java 8. I have a problem in creating a list with few fields compared to when I get a list with all the fields of a table.

@Query("SELECT c.idCliente, c.nome, c.cognome, c.username, c.email FROM Cliente c WHERE c.username LIKE %:username%")
List<Cliente> findClienteByUsername(@Param("username") String username);

The result is:

[
   3,
   null,
   null,
   "user",
   "aaa"
]

But when show all fields get this:

{"idCliente":3,"username":"user","nome":null,"cognome":null,"dataNascita":null,"email":"aaa","password":"ciao","dataCreazione":"2018-11-23T21:33:31.000+0000","instagram":null,"facebook":null,"google":null,"twitter":null,"attivo":"1","ultimaSospensione":null}

Why can't I get the field names along with the values?

Answer 1

While you have to select a few fields you have to go with Spring Projection through DTO class. You have to define the constructor with the selected fields.

@Query("SELECT new Cliente(c.idCliente, c.nome, c.cognome, c.username, c.email) FROM Cliente c WHERE c.username LIKE %:username%")
List<Cliente> findClienteByUsername(@Param("username") String username);

You can refer below link with detailed information. https://smarterco.de/spring-data-jpa-query-result-to-dto/

Or you can do the manual translation for each row using a mapper function.

 @Query("SELECT c.id, c.nome, c.cognome, c.username, c.email FROM Cliente c WHERE c.username LIKE %:username%")
List<Object[]> findClientDeatailsByuserName(@Param("username")String username);

Answer 2

Try this one: Create the below mentioned constructor into an Cliente entity class.

Cliente(int idCliente,String noame,String cognome,String username,String email){
   this.idCliente=idCliente;
   this.nome=nome;
   this.cognome=cognome;
   this.username=username;
   this.email=email;   
 }

Call the query as:

@Query("SELECT new packageName.Cliente(c.idCliente, c.nome, c.cognome, c.username, c.email) FROM Cliente c WHERE c.username LIKE %:username%")
List<Cliente> findClienteByUsername(@Param("username") String username);

It will show all fields with value.