Spring Boot JPA returns List of List not List of Object - spring

Question

I am new to spring boot jpa. I would like to get return type as List but I am getting just List
My Entity Class
#Component
#Entity
#Table(name = "USERDB.USERS")
public class User() {
#Id
#GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "MY_SEQ")
#SequenceGenerator(sequenceName = "MY_SEQ_NAME", allocationSize = 1), name = "MY_SEQ")
#Column(name = "userId")
private long id;
#Column(name = "firstName")
private String fName;
#Column(name = "midName")
private String mName;
#Column(name = "lastName")
private String lName;
#Column(name = "email")
private String email;
#Column(name = "createdDate")
private Timestamp createdOn;
public User() {
this.createdOn = new Timestamp(System.currentTimeMillis()
}
//SETTERS & GETTERS
}
My Repository;
public interface UserRepository extends JpaRepository<User, String> {
#Query("SELECT id fName, lastName, email FROM User u WHERE u.fName=(:fName)")
public List<User> findByEmail(#Param("fName") String fName);
}
All I wanted is to get a json response as a User Array with key value pair like below
[
[
"id": 1001,
"fName": John",
"lName": "Doe",
"email": "johnd#example.com"
],
[
"id": 1002,
"fName": "John",
"lName": "Simmons",
"email": "johns#example.com"
],
]
but I am getting a list with just values as below.
[
[
1001,
"John",
"Doe",
"johnd#example.com"
],
[
1002,
"John",
"Simmons",
"johns#example.com"
],
]
I am not sure where I am doing wrong or is this how I am supposed to get ? This is a hypothetical example of my actual program. Please excuse me for any errors.
Here is my controller class
#Restcontroller
public class UserController {
#Autowired
UserRepository repo;
#GetMapping("/user/{fname}")
public List<User> getUserByName(
#PathVariable("fname") String fname) {
return repo.findByEmail(fname);
}
}

Answer 1

A few points on your code:
public interface UserRepository extends JpaRepository<User, String> {
Query("SELECT id fName, lastName, email FROM User u WHERE u.fName=(:fName)")
public List<User> findEmails(#Param("fName") String fName);
}
You are creating the repository with JpaRepository<User, String> but in your class User id is not of type String. Consider making the ID field a String.
The method is findEmails but it is returning a List<User>? I would expect such a function to return List<String> - each string of course being an email. You may consider renaming this function to avoid future confusion. Not a big deal though.
In your query:
#Query("SELECT id fName, lastName, email FROM User u WHERE u.fName=(:fName)")
You should change this to:
#Query("SELECT u.id u.fName, u.lastName, u.email FROM User u WHERE u.fName=(:fName)")
That should fix the serialization issue you are having.

Answer 2

I very much agree with the suggestion of Fermi-4. Using a better naming convention is key to have a better easy manageable code. You should follow them. To solve your problem, just do the following and it will solve your problem.
public interface UserRepository extends JpaRepository<User, long> {
public List<User> findByFname(String fName);
}
Also, consider changing USER Entity definition to add serializable implementation as below
#Component
#Entity
#Table(name = "USERDB.USERS")
public class User implements Serializable{
/**
*
*/
private static final long serialVersionUID = 3L;

Answer 3

Create additional User constructor with only few arguments that you wish to fetch from table
public User(long id, String fName, String lastName, String email) {
this.id = id;
this.fName = fName;
this.lastName = lastName;
this.email = email;
}
Adjust JP query like following
#Query("SELECT new com.package.User(u.id, u.fName, u.lastName, u.email) FROM User u WHERE u.fName = :fName")
public List<User> findByEmail(#Param("fName") String fName);
replace com.package with your User's actual package