why hibernate creates a join table for unidirectional OneToMany?

Question

Why hibernate uses a join table for these classes?

@Entity
public class CompanyImpl {
    @OneToMany
    private Set flights;


@Entity
public          


        

Answer 1

Because that's how it's designed, and what the JPA spec tells it to map such an association. If you want a join column in the Flight table, use

@Entity
public class CompanyImpl {
    @OneToMany
    @JoinColumn(name = "company_id")
    private Set<Flight> flights;
}

This is documented.

Answer 2

Hibernate uses an association table to map the relationship, whilst the other table which is the many side does not not that any table exist. It will then create a mapper instead.

The documentation states that using @OneToMany and @ManyToMany you can map Collections, Lists, Maps and Sets of associated entities.

if you do not specify @joincolumn, this is as regards your question, a unidirectional one to many with join table is used. The table name is the concatenation of the owner table name, _, and the other side table name. The foreign key name(s) referencing the owner table is the concatenation of the owner table, _, and the owner primary key column(s) name.

So if you do not want to create a join table(mapper) using the one to many you may have to specify the @joinColumn.

@Entity
public class CompanyImpl {
    @OneToMany
     @JoinColumn(name=flights_id)
    private Set<Flight> flights;


@Entity
public class Flight {