How to correctly handle DTO conversion in Micronaut Reactive - project-reactor

Question

Lets say we are working with Micronaut Reactive (Project Reactor) and we would like to create a user account. SignUp DTO is represented by the following Kotlin class:
#Introspected
data class SignUpDto(
#field:Schema(example = "admin")
#field:NotBlank #field:Max(value = 255) var username: String? = null,
// rest is omitted for brevity
)
In order to create and persist an account entity in the database, first, we have to convert the SignUpDTO to the account entity represented by the kotlin class below:
#Entity(name = "Accounts")
#Where("#.active = true")
open class AccountEntity {
#Id
#GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "accounts_sequence_generator")
#SequenceGenerator(name = "accounts_sequence_generator", sequenceName = "sequence_accounts")
#Column(name = "id", nullable = false, unique = true)
open var id: Long? = null
#Column(name = "username", nullable = false, unique = true, updatable = false, length = 255)
open var username: String? = null
#Column(name = "active", nullable = false)
open var active: Boolean? = true
#ManyToMany(fetch = FetchType.LAZY, cascade = [CascadeType.PERSIST, CascadeType.MERGE])
#JoinTable(name = "accounts_roles",
joinColumns = [JoinColumn(name = "accounts", referencedColumnName = "id")],
inverseJoinColumns = [JoinColumn(name = "roles", referencedColumnName = "id")])
open var roles: MutableSet<RoleEntity> = mutableSetOf()
// rest is omitted for brevity
}
As you can see, AccountEntity has a many-to-many relationship on a RoleEntity. For completeness, RoleEntity is shown below:
#Entity(name = "Roles")
open class RoleEntity {
#Id
#GeneratedValue(strategy = GenerationType.SEQUENCE)
#Column(name = "id", nullable = false, unique = true)
open var id: Long? = null
#Column(name = "role", nullable = false, unique = true)
#Enumerated(EnumType.STRING)
open var role: Role? = null
#Column(name = "description", nullable = false, length = 500)
open var description: String? = null
// rest is omitted for brevity
}
Application defines a RoleRepository as follows:
#Repository
interface RoleRepository : ReactorCrudRepository<RoleEntity, Long> {
fun findByRole(role: Role): Mono<RoleEntity>
}
We are interested in mapping a SignUpDTO request to an account entity and persisting that entity in a reactive way. Function that does the converting is given below:
fun convertSignUpToAccountEntity(#Valid signUpDto: SignUpDto): AccountEntity {
return AccountEntity().apply {
this.username = signUpDto.username
this.active = true
this.roles.add(**add a user role here**)
}
}
Given that the RoleRepository is available to this function, how would one fetch the Role.User entity and add it to the list of account roles in a reactive way, since calling block just indefinitely blocks the calling thread? Is there a way to handle this in a reactive way?

Answer 1

You can have something like this:
return Flux.fromIterable(Arrays.asList("role1", "role2"))
.flatMap(role -> roleRepository.findByRole(role))
.collectList()
.map(roles -> convertSignUpToAccountEntity(signUpDto, roles))
.flatMap(accountEntityRepository::save);