In Spring Boot 2, is it possible to auto-generate a JoinTable with a unique constraint? - spring

Question

I'm using Spring Boot 2 and PostGres 10. I have created the following entities, Roles and Privileges,
#Data
#Entity
#Table(name = "Roles")
public class Role {
public enum Name {
USER,
ADMIN
}
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private UUID id;
#Column(unique=true)
#Enumerated(EnumType.STRING)
private Name name;
#ManyToMany
#JoinTable(
name = "roles_privileges",
joinColumns = #JoinColumn(
name = "role_id", referencedColumnName = "id"),
inverseJoinColumns = #JoinColumn(
name = "privilege_id", referencedColumnName = "id"))
private Collection<Privilege> privileges;
}
Privilege is
#Data
#Entity
#Table(name = "Privileges")
public class Privilege {
public enum PrivilegeName {
SUPER_ADMIN,
USER
}
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private UUID id;
#Column(unique=true)
#Enumerated(EnumType.STRING)
private PrivilegeName name;
#ManyToMany(mappedBy = "privileges")
private Collection<Role> roles;
}
Then I have this in my application.properties
spring.jpa.properties.hibernate.dialect = org.hibernate.dialect.PostgreSQLDialect
spring.jpa.hibernate.ddl-auto=update
spring.jpa.hibernate.show-sql=true
spring.datasource.url=jdbc:postgresql://${PG_DB_HOST:localhost}:5432/${PG_DB_NAME}
spring.datasource.username=${PG_DB_USER}
spring.datasource.password=${PG_DB_PASS}
When my tables are generated, the roles_privileges table is generated like so ...
cardmania=# \d roles_privileges ;
Table "public.roles_privileges"
Column | Type | Modifiers
--------------+------+-----------
role_id | uuid | not null
privilege_id | uuid | not null
Foreign-key constraints:
"fk5duhoc7rwt8h06avv41o41cfy" FOREIGN KEY (privilege_id) REFERENCES privileges(id)
"fk629oqwrudgp5u7tewl07ayugj" FOREIGN KEY (role_id) REFERENCES roles(id)
Are there any other annotations or other Java code I can add so that when my join table is created, the role_id/privilege_id has a unique key generated?

Answer 1

To force Hibernate to create a primary key with both columns, you have to change Collection by Set
public class Role {
#ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE})
#JoinTable(
name = "roles_privileges",
joinColumns = #JoinColumn(
name = "role_id", referencedColumnName = "id"),
inverseJoinColumns = #JoinColumn(
name = "privilege_id", referencedColumnName = "id"))
private Set<Privilege> privileges;
}
And:
public class Privilege {
#ManyToMany(mappedBy = "privileges")
private Set<Role> roles;
}

Answer 2

You will not see a unique constraint but you will see the following table
create table roles_privileges (
role_id binary not null,
privilege_id binary not null
)
But you can explicitly declare your unique constraint
#ManyToMany
#JoinTable(
name = "roles_privileges",
joinColumns = #JoinColumn(name = "role_id", referencedColumnName = "id"),
inverseJoinColumns = #JoinColumn(
name = "privilege_id", referencedColumnName = "id"),
uniqueConstraints = #UniqueConstraint(columnNames = {"role_id",
"privilege_id"},
name = "rolesPrivilegesConstraint")
)
private Collection<Privilege> privileges;