Order of saving when having parent-child relationship between domain classes If we have domain classes A and B with a parent-child relationship, where class B belongs to class A, which entity should be saved first in Grails? In service class: A a; B b; func() { b.save(failOnError :true) a.save(flush:true , failOnError :true) } I am getting NonUniqueKeyException, DublicateKeyException post grails upgrade to v6.2.3 There are no code changes in this code area, just grails upgrade. Tried to save parent first, but the I am getting unable to insert NULL B.ID