How to create an entity's relationship to itself? For example, hierarchical folders - jhipster

Question

I'm trying to create a hierarchical folder structure. Here's my Folder entity:
$ yo jhipster:entity Folder
The entity Folder is being created.
Generating field #1
? Do you want to add a field to your entity? Yes
? What is the name of your field? name
? What is the type of your field? String
? Do you want to add validation rules to your field? No
=================Folder=================
name (String)
Generating field #2
? Do you want to add a field to your entity? Yes
? What is the name of your field? parentId
? What is the type of your field? Long
? Do you want to add validation rules to your field? No
=================Folder=================
name (String)
parentId (Long)
Generating field #3
? Do you want to add a field to your entity? No
=================Folder=================
name (String)
parentId (Long)
I'm trying to map out just what I need to provide jhipster's entity generator to make it work. This is what I have so far...
Generating relationships with other entities
? Do you want to add a relationship to another entity? Yes
? What is the name of the other entity? Folder
? What is the name of the relationship? parent
? What is the type of the relationship? one-to-many
? What is the name of this relationship in the other entity? child
Am I on the right track? How do I create the child many-to-one relationship? I get a warning if I try to create it with the Folder entity. There's no way to generate it afterwards.

Answer 1

You can use https://jhipster.github.io/jdl-studio/ for writing as jdl for creating entities.
Please visit https://jhipster.github.io/jhipster-uml/#jdl for more information.
This is a sample JDL that has relationship to itself :
entity RankProperties {
rank Integer required,
minExp Integer required,
maxExp Integer required,
maxStamina Integer required,
maxAlly Integer required,
maxTeam Integer required
}
enum TaskMode {
NO_CONTINUE_STAGE_COUNT,
STAGE_COUNT,
STAGE_ID
}
entity Task {
taskMode TaskMode required,
value Integer required
}
relationship ManyToOne {
Task{parent} to Task
}
dto all with mapstruct
service all with serviceClass

Answer 2

I recommend to use jdl model.
entity A { property1 String }
relationship OneToMany {
A{sons} to A{parent}
}
The model generates a Entity java class like (some annotations ignored):
class A {
#OneToMany(mappedBy="parent")
private Set<A> sons = new HashSet<>();
#ManyToOne
private A parent;
}