database - JPA/Hibernate Difference MappedSuperclass and Entity Abstract Class -


i know difference between mappedsuperclass , entity abstract class when 1 wants derive super class in hibernate. know hibernate not create table in database mappedsuperclass. read in javaee doc "abstract entities concrete entities cannot instantiated". since cannot instantiated, deduce there no matching table in database. right?

if so, virtually difference between using mappedsuperclass , entity abstract class , impact on software , in database in each case?

a mappedsuperclass uses inheritance field , code reuse. example, if want entities have long id , long version field, make them extend baseentity class annotated mappedsuperclass containing these 2 fields, along getters, setters, etc. never have entity having association baseentity: association specific subclass of baseentity.

a parent entity used "entity polymorphism". example, imagine having 2 kinds of message: emailmessage , smsmessage. both contain source, target, , body. emailmessage have email address , subject, whereas smsmessage have phone number.

and imagine having person entity containing collection of sent messages, of type message. collection in fact contain instances of emailmessage , of smsmessage. hibernate decide 1 instantiate depending on inheritance strategy used inheritance mapping:

  • all messages stored in same table, , hibernate use discriminator column containing type of message
  • the emailmessage stored in 1 table, , smsmessage stored in one
  • or fields common both entities (source, target, body) stored in comon table, fields specific emailmessage in second table, , fields specific smsmessage in third table.

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