Using junction tables created in schema within Spring Boot JDBC - sql

Question

I'm trying out pre-defining my database structure using SQL schema and then utilising it within my Kotlin code. I'm using Spring Boot and Spring Data JDBC.
Here's what I currently have so far:
My User class:
data class User(
#Column(name = SqlQueries.Users.Entries.id) // "user_id"
val id: String?,
#Column(name = SqlQueries.Users.Entries.firstName) // "user_first_name"
var firstName: String = "Joe",
#Column(name = SqlQueries.Users.Entries.lastName) // "user_last_name"
var lastName: String = "Bloggs",
#Column(name = SqlQueries.Users.Entries.username) // "user_username"
var username: String = "${firstName}.${lastName}",
#Column(name = SqlQueries.Users.Entries.password) // "user_password"
#JsonIgnore
var password: String = "password1",
#Column(name = SqlQueries.Users.Entries.isActive) // "user_is_active"
val isActive: Boolean = true,
)
My UserRole class:
data class UserRole(
#Column(name = SqlQueries.Lookups.UserRoles.Entries.id)
val id: Int? = null,
#Column(name = SqlQueries.Lookups.UserRoles.Entries.roleName)
val name: String = "",
)
My Schema:
-- ===================================================================================
-- Lookup Tables
-- ===================================================================================
-- Creates our User Table if one does not exist within the database already.
CREATE TABLE IF NOT EXISTS table_users(
user_id VARCHAR(60) DEFAULT RANDOM_UUID() UNIQUE PRIMARY KEY,
user_first_name VARCHAR NOT NULL,
user_last_name VARCHAR NOT NULL,
user_username VARCHAR NOT NULL UNIQUE,
user_password VARCHAR NOT NULL,
user_is_active VARCHAR NOT NULL
);
-- ===================================================================================
-- Lookup Tables
-- ===================================================================================
-- Creates our Roles Lookup Table if one does not already exist within the database.
CREATE TABLE IF NOT EXISTS lookup_roles(
role_id SMALLINT AUTO_INCREMENT UNIQUE PRIMARY KEY,
role_name VARCHAR NOT NULL UNIQUE
);
-- ===================================================================================
-- Junction Tables
-- ===================================================================================
-- Creates our User/Role Junction table if one does not already exist within the database.
-- This will be the foundation of a many to many relationship between the two entities.
CREATE TABLE IF NOT EXISTS junction_user_role(
user_id VARCHAR(60),
role_id SMALLINT,
CONSTRAINT pk_user_role PRIMARY KEY (user_id, role_id),
CONSTRAINT fk_user FOREIGN KEY (user_id) REFERENCES table_users (user_id),
CONSTRAINT fk_role FOREIGN KEY (role_id) REFERENCES lookup_roles (role_id)
);
As you can see, I've created a User, Role and User/Role table. This is designed to have a many to many relationship.
I'm in the dark with being able to "access" the relationship as a variable which I can use later on.
In my previous "prototype" which had a different design concept I used the following format:
User class:
...
#ManyToMany(fetch = FetchType.EAGER)
#Column(name = "user_roles")
var userRoles: MutableSet<Role> = mutableSetOf(),
...
How would I define and implement this with the new way of doing it?

Answer 1

I don't really speak Kotlin, but I try anyway. Please use ChatGPT or personal experience to fix Kotlin errors ;-)
The first step is to identify the aggregates an what belongs to which aggregate.
I'd suggest that you have a UserRole and a User aggregate, with the later owning the relationship.
This implies that you need to add the relationship to the User, which is your aggregate root for the User aggregate.
Since Role is a different aggregate you'd reference it by id, and you need a separate entity to hold that id
data class User (
...
#MappedCollection(idColumn="user_id")
val roles: Set<RoleRef>
)
data class RoleRef(
val roleId: AggregateReference<Role, Int>
)
If you want to navigate from UserRole to all the User entities having that role, you'd create a repository method in the UserRepository for this.
How this works is detailed in https://spring.io/blog/2018/09/24/spring-data-jdbc-references-and-aggregates
Also related: Spring Data JDBC many to many relationship management