Can I write my own Queries in a Spring boot web app? - postgresql

Question

I'm making my first springboot web app, and trying to display some information from a postgresql server. When trying to get some information out of the database, it returns an empty list. By what I can see in the console, it tries to query with the wrong parameters.
In my DB I have a table with three fields: "userId", "firstName", and "surName".
From what i can understand, Hibernate tries to query with the parameters "users0_.user_id", "users0_user_id", "users0_.sur_name".
To fix this i want to write my own queries or fix the current one. How do I do this?
As you can see I have checked the results of the query with some System.Out.print statements.
The first one returned a list.size() of 0,
and the second one returned a value of null.
Console displaying what I think is the query info
This is the function in my UserController class used to display the users' info.
#RequestMapping("/users")
public String getUsers(Model model) {
List <users>users = (List<users>) userServ.listAll();
System.out.print("THE SIZE WITH STRING CONCATINATION IS: " + users.size());
model.addAttribute("users", users);
System.out.print("THE NAME OF USER WITH INDEX =2 IS: " + userServ.getById(2).getFirstName());
return "showUsers";
}
The entity/domain-class for a user:
#Entity
#Table(name="users")
public class users implements Serializable{
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private long userId;
private String firstName;
private String surName;
private long getId() { return userId; }
public void setId(long id) {this.userId = id;}
public String getFirstName() { return firstName; }
public String getSurName() { return surName; }
public void setSurname(String surName) {this.surName = surName; }
}
This is the interface of the repository used to retrieve users from the DB:
import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
import org.springframework.data.repository.CrudRepository;
import com.svein.models.users;
public interface UserRepository extends CrudRepository<users, Long> {
}
This is the service class for the users:
#Service
public class UserServiceImp implements userService{
#Autowired
private UserRepository userRepo;
#Override
public List<users> listAll() {
List<users> users = new ArrayList<>();
userRepo.findAll().forEach(users::add);
return users;
}
#Override
public users getById(long id) {
return userRepo.findById(id).orElseGet(users::new);
}
#Override
public users saveOrUpdate(users user) {
userRepo.save(user);
return null;
}
#Override
public void delete(Long id) {
userRepo.deleteById(id);
}
}
I was hoping to adjust or replace the current query, but maybe there is something alse wrong with the code. As I said, I'm quite new to this, but thought it was weird that i had not written a single line of SQL, and in a different project THAT showed signs of retrieving the right information(from a different DB). How does the class know what to query for?

Answer 1

You need to add an #Query annotation on top of query function you want to write in your UserRepository class.
For e.g
import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
import org.springframework.data.repository.CrudRepository;
import com.svein.models.users;
public interface UserRepository extends CrudRepository<users, Long> {
#Query("Select * from users")
List<users> findAllUsers();
}
Alternatively in your UserServiceImpl, userRepo.findAll() should work.You do not need to loop through each user and return it to list. You should simply return userRepo.findAll().
Following url would give you more idea about how to write your own query.
https://www.baeldung.com/spring-data-jpa-query