JavaPersistenceWithHibernate第二版笔记-第六章-Mapping inheritance-002Table per concrete class with implicit polymorphism(@MappedSuperclass、@AttributeOverride)

一、结构

二、代码

1.

2.

3.

三、存在的问题

1.it doesn’t support polymorphic associations very well。You can’t have another entity mapped with a foreign key “referencing BILLINGDETAILS ”—there is no such table. This would be problematic in the domain model, because BillingDetails is associated with User ; both the CREDITCARD and BANKACCOUNT tables would need a foreign key reference to the USERS table. None of these issues can be easily resolved, so you should consider an alternative mapping strategy.

2.查父类时要查每个表。Hibernate must execute a query against the superclass as several SQL SELECT s, one for each concrete subclass. The JPA query select bd from BillingDetails bd requires two SQL statements:

3.several different columns, of different tables, share exactly the same semantics.

结论：We recommend this approach (only) for the top level of your class hierarchy,where polymorphism isn’t usually required, and when modification of the superclass in the future is unlikely.

You can do anything you set your mind to, man!