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29 строки
1.4 KiB
Plaintext
29 строки
1.4 KiB
Plaintext
2023
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https://www.baeldung.com/hibernate-inheritance
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https://github.com/eugenp/tutorials/tree/master/persistence-modules/hibernate-mapping
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@MappedSuperclass (no @Entity)
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This (base) class no longer has an @Entity annotation, as it won't be persisted in the database by itself.
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Childrens will just duplicate columns for inherited fields
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for @Inheritance(strategy = InheritanceType.SINGLE_TABLE)
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@DiscriminatorColumn (at base class), @DiscriminatorValue
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DiscriminatorFormula
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for @Inheritance(strategy = InheritanceType.JOINED)
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The disadvantage of this inheritance mapping method is that retrieving entities requires joins between tables,
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for @Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
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The resulting schema is similar to the one using @MappedSuperclass.
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But Table per Class will indeed define entities for parent classes,
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allowing associations and !!!"polymorphic"!!! queries as a result.
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This is not that different from merely mapping each entity without inheritance.
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The distinction is clear when querying the base class, which will return all the subclass records
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as well by using a UNION statement in the background.
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The use of UNION can also lead to inferior performance when choosing this strategy.
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Another issue is that we can no longer use identity key generation.
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