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kotlinlang

hello, could I ask for some advice, link to article or github repo to a project showing/explaining best practices of rest api with jpa (entities with relations ex. @ManyToOne). Ive seen various tuts showing data classes as entities, other saying it's bad idea cause ID is null before saving to db and equals changes which may/will cause problems etc., others hardcoding hashcode to constant value in @MappedSuperclass and inheriting simple class with id and hashcode... how should it be done properly? appreciate any info on the matter