Micronaut Data JDBC: How to map a one-to-many relation using enums? - kotlin

Question

I would like to map a unidirectional one-to-many relation, using Micronaut Data annotations. Considering the object and database models described below, how to map that using Micronaut annotations?
Object model:
import io.micronaut.serde.annotation.Serdeable
#Serdeable
enum class Role {
Admin, Manager
}
import io.micronaut.data.annotation.GeneratedValue
import io.micronaut.data.annotation.Id
import io.micronaut.data.annotation.MappedEntity
import io.micronaut.serde.annotation.Serdeable
#Serdeable
#MappedEntity
data class User(
#field:Id
#field:GeneratedValue
var id: Long? = null,
val username: String,
// How to map?
var roles: Set<Role>?
)
Database model with many-to-many (DDLs for PostgreSQL):
CREATE TABLE "user"
(
id SERIAL PRIMARY KEY,
username VARCHAR(30) NOT NULL UNIQUE
);
CREATE TABLE "role"
(
id INTEGER PRIMARY KEY,
name VARCHAR(40) NOT NULL
);
CREATE TABLE "user_role"
(
user_id INTEGER REFERENCES "user" (id),
role_id INTEGER REFERENCES "role" (id)
);
INSERT INTO "role" (id, name) VALUES (1, 'Admin'), (2, 'Manager');
Or another option, a simpler database model using one-to-many (PostgeSQL):
CREATE TABLE "user"
(
id SERIAL PRIMARY KEY,
username VARCHAR(30) NOT NULL UNIQUE
);
CREATE TYPE role_name AS ENUM ('Admin', 'Manager');
CREATE TABLE "user_role"
(
user_id INTEGER NOT NULL REFERENCES "user" (id),
role_id INTEGER NOT NULL REFERENCES "role" (id),
CONSTRAINT user_role_uk UNIQUE (user_id, role_id)
);
You may suggest modifications to any database model to allow the one-to-many relation in the object model.

Answer 1

Here are two out of the multiple ways that it could be done. I combined them into one example out of laziness.
#Serdeable
enum class Role {
Admin, Manager;
}
#Serdeable
#MappedEntity
data class UserRole(
#field:Id
#GeneratedValue
var id: Long? = null,
#Nullable
#Relation(value = Relation.Kind.MANY_TO_ONE)
val user: User?,
val role: Role
)
#Serdeable
#MappedEntity
class User(
#field:Id
#field:GeneratedValue
var id: Long? = null,
val username: String,
#MappedProperty(definition = "VARCHAR(30)[]", type = DataType.STRING_ARRAY)
var roles: Set<Role>?,
#Relation(value = Relation.Kind.ONE_TO_MANY, mappedBy = "user", cascade = [Cascade.ALL])
var userRoles: Set<UserRole>?
)
#JdbcRepository(dialect = Dialect.POSTGRES)
#Join(value = "userRoles", type = Join.Type.LEFT_FETCH)
interface UserRepository : CrudRepository<User, Long> {
}
CREATE TYPE role_name AS ENUM ('Admin', 'Manager');
CREATE TABLE "user"
(
id SERIAL PRIMARY KEY,
username VARCHAR(30) NOT NULL UNIQUE,
roles VARCHAR(15)[]
);
CREATE TABLE "user_role"
(
id BIGINT PRIMARY KEY GENERATED ALWAYS AS IDENTITY,
user_id INTEGER REFERENCES "user" (id),
role role_name NOT NULL,
CONSTRAINT user_role_uk UNIQUE (user_id, role)
);