What is the purpose of mapstruct?

Question

MySQL

I didn’t find anything in RuNet on mapstruct in which cases should it be used?
As I understand it, issuing an entity (Entity) in REST json is a bad tone, but why, then, in all courses, mapping is not affected or misunderstood?
If possible, give examples of using mapstruct from real projects

Answer 1

user_id | transport_type | transport_id
transport_type - will indicate in which table to look for transport_id, you can call transport_table and write the table name right away, but this is not kosher)

Answer 2

ПользовательТранспорта:
   имя
   транспорт пользователя = ManyToMany(ТипТранспорта)
...

ТипТранспорта
    название
...

Answer 3

Can be done on 2 tables.
table user_transport:
user_id | transport_id
table transport:
id | params | value
1 | transport_type | bus
1 | name_param1 | value1
1 | name_param2 | value2
and so on
2 | transport_type | metro
2 | name_param1 | value1
2 | name_param2 | value2
and so on