DuplicateMappingException contains physical column name referred to by multiple logical column names on adding passportId to the Student entity

This code is causing the following exception on the startup

Caused by: org.hibernate.DuplicateMappingException: Table [student] contains physical column name [passport_id] referred to by multiple logical column names: [passport_id], [passportId]

I’m using H2 in-memory database.

Student entity:

@Entity
public class Student {

    @Id
    @GeneratedValue
    private Integer id;
    @Column(nullable = false, length = 250)
    private String name;
    private Integer passportId; // adding this will cause DuplicateMappingException

    @OneToOne
    private Passport passport;
    // getters and setters omitted for brevity
}

Passport entity:

@Entity
public class Passport {

    @Id
    @GeneratedValue
    private Integer id;
    @Column(nullable = false, length = 250)
    private String number;
    // getters and setters omitted for brevity
}

Question 1: What is the reason for org.hibernate.DuplicateMappingException?

Question 2: Why does adding the following annotation to passportId in the Student entity resolve the issue?

@Column(name = "passport_id", insertable = false, updatable = false)
private Integer passportId; // this resolves DuplicateMappingException

PS: I know similar questions has been asked earlier but I couldn’t understand the answer for these two questions from those other threads.

Answer

Answer 1

The reason is that you have two writable mappings for the same database column and this is not allowed

Answer 2

Making one of the mappings read-only solves the problem because then only one mapping will be writable