The document discusses different approaches for mapping entity and value types, collections, and associations between entity classes in Hibernate. It provides examples of mapping value type collections as lists, sets, maps, and bags. For entity associations, it demonstrates one-to-many and many-to-one mappings. It also summarizes different inheritance mapping strategies in Hibernate like table per concrete class, table per class hierarchy, and table per subclass.

1. Mapping collections and entity associations Session - II

2. Difference between Entity & Value Types Entity Has Shared references Should have database identity No default transitive persistence Value Types It’s lifespan is bounded by the lifespan of the owning entity instance An object of value type has no database identity Has default transitive persistence.

3. Mapping of collections (Value Types)

4. Example For Value Type Mapping

5. Mapping Value Type Mapping a single data type Usage: <set name=&quot;images&quot; table=&quot;ITEM_SET_IMAGES&quot;> <key column=&quot;IT_ID&quot;/> <element type=&quot;string&quot; column=&quot;IMAGENAME&quot;/> </set> Mapping a Whole table using composite element. Usage: <set name=&quot;images&quot; table=&quot;ITEM_SET_IMAGES&quot;> <key column=&quot;IT_ID&quot;/> <composite-element class=&quot;ImageDetails&quot;> <property name=&quot;imagename&quot; column=&quot;IMAGENAME&quot; not-null=&quot;true&quot;/> <property name=&quot;imagLoc&quot; column=&quot;IMAGELOC&quot; not-null=&quot;true&quot;/> </composite-element> </set>

6. Different Choice For Value Type Collection Implementation Lists :- preserving the position of each element with an additional index column in the collection table. :- Initialize with a java.util.ArrayList for <list>. Example:- Usage:- <list name=“images&quot; table=&quot;ITEM_IMAGE&quot;> <key column=&quot;ITEM_ID&quot;/> <list-index column=&quot;POSITION&quot;/> <element type=&quot;string&quot; column=“FILENAME&quot; not-null=&quot;true&quot;/> </list>

7. Sets :- The order of its elements isn’t preserved, and duplicate elements aren’t allowed. :- Initialize with a java.util.HasSet for <set> :- A java.util.SortedSet can be mapped with <set>, and the sort attribute can be set to either a comparator or natural ordering for in-memory sorting. Initialize the collection with a java.util.TreeSet instance. Example:- Usage:- <set name=“images&quot; table=&quot;ITEM_IMAGE&quot;> <key column=&quot;ITEM_ID&quot;/> <element type=&quot;string&quot; column=“FILENAME&quot;/> </set> SortedSet <set name=&quot;images&quot; table=&quot;ITEM_IMAGE&quot; sort=&quot;natural&quot; > <key column=&quot;ITEM_ID&quot;/> <element type=&quot;string&quot; column=&quot;FILENAME&quot; /> </set>

8. Maps :- A java.util.Map can be mapped with <map>, preserving key and value pairs. Use a java.util.HashMap to initialize a property. :-A java.util.SortedMap can be mapped with <map> element, and the sort attribute can be set to either a comparator or natural ordering for in-memory sorting. Initialize the collection with a java.util.TreeMap instance. Example:- Usage:- < map name=&quot;images&quot; table=&quot;ITEM_IMAGES&quot;> <key column=&quot;ITEM_ID&quot;/> <map-key column=“IMAGENAME&quot; type=&quot;string&quot;/> <element type=&quot;string&quot; column=“FILENAME&quot; not-null=&quot;true&quot;/> </map> SortedMap <map name=&quot;images&quot; table=&quot;ITEM_IMAGE&quot; sort=&quot;natural&quot;> <key column=&quot;ITEM_ID&quot;/> <map-key column=&quot;IMAGENAME&quot; type=&quot;string&quot;/> <element type=&quot;string&quot; column=&quot;FILENAME&quot; not-null=&quot;true&quot;/> </map>

9. Bags :- Possible duplicates, no element order is preserved. :- A java.util.Collection can be mapped with <bag> or <idbag>. :- Hibernate supports persistent bags (it uses lists internally but ignores the index of the elements). :- Initialize with a java.util.ArrayList Example :- Usage :- <idbag name=&quot;images&quot; table=&quot;ITEM_IDBAG_IMAGES&quot;> <collection-id type=&quot;long&quot; column=“ITEM_IMAGE_ID&quot;> <generator class=&quot;sequence&quot;/> </collection-id> <key column=&quot;ITEM_ID&quot;/> <element type=&quot;string&quot; column=&quot;FILENAME&quot; not-null=&quot;true&quot;/> </idbag>

10. Mapping of associations between entity classes (Entity) Scenario

11. One-to-many Each Item has a number of Bids Usage:- <set name=&quot;bids&quot; inverse=&quot;true&quot; cascade=&quot;save-update,delete,delete-orphan&quot;> <key column=&quot;ITEM_ID&quot;/> <one-to-many class=&quot;Bid&quot;/> </set>

12. Many-to-one Many bids may point to a single Item Usage:- <many-to-one name=&quot;item“ column=&quot;ITEM_ID“ class=&quot;Item&quot;/> This indicates that the collection contains not value type instances, but references to entity instances. Hibernate now knows how to treat shared references and the lifecycle of the associated objects

13. Demo

14. Inheritance

15. Approaches Table per concrete class with implicit polymorphism Use no explicit inheritance mapping, and default runtime polymorphic behavior. Table per concrete class with Unions Discard polymorphism and inheritance relationships completely from the SQL schema. Table per class hierarchy Enable polymorphism by denormalizing the SQL schema, and utilize a type discriminator column that holds type information. Table per subclass Represent is a (inheritance) relationships as has a (foreign key) relationships.

16. Table per concrete class with Union Scenario

17. Usages: <hibernate-mapping> <class name=&quot;BillingDetails“ abstract=&quot;true&quot; > <id name=&quot;id“ column=&quot;BILLING_DETAILS_ID“ type=&quot;long&quot;> <generator class=&quot;native&quot;/> </id> <property name=&quot;name“ column=&quot;OWNER“ type=&quot;string&quot;/> <union-subclass name=&quot;CreditCard&quot; table=&quot;CREDIT_CARD&quot;> <property name=&quot;number&quot; column=”NUMBER”/> <property name=&quot;expMonth&quot; column=&quot;EXP_MONTH&quot;/> <property name=&quot;expYear&quot; column=&quot;EXP_YEAR&quot;/> </union-subclass> <union-subclass name=&quot;BankAccount&quot; table=&quot;BANK_ACCOUNT&quot;> ... </class> </hibernate-mapping>

18. Table per class hierarchy Scenario

19. Usage: <hibernate-mapping> <class name=&quot;BillingDetails“ table=&quot;BILLING_DETAILS&quot;> <id name=&quot;id“ column=&quot;BILLING_DETAILS_ID“ type=&quot;long&quot;> <generator class=&quot;native&quot;/> </id> <discriminator column=&quot;BILLING_DETAILS_TYPE“ type=&quot;string&quot;/> <property name=&quot;owner“ column=&quot;OWNER“ type=&quot;string&quot;/> ... <subclass name=&quot;CreditCard“ discriminator-value=&quot;CC&quot;> <property name=&quot;number&quot; column=&quot;CC_NUMBER&quot;/> <property name=&quot;expMonth&quot; column=&quot;CC_EXP_MONTH&quot;/> <property name=&quot;expYear&quot; column=&quot;CC_EXP_YEAR&quot;/> </subclass> <subclass name=”BankAccount” discriminator-value=”BA”> ... </class> </hibernate-mapping>

20. Table per subclass Scenario

21. Usage <hibernate-mapping> <class name=&quot;BillingDetails“ table=&quot;BILLING_DETAILS&quot;> <id name=&quot;id“ column=&quot;BILLING_DETAILS_ID“ type=&quot;long&quot;> <generator class=&quot;native&quot;/> </id> <property name=&quot;owner“ column=&quot;OWNER“ type=&quot;string&quot;/> <joined-subclass name=&quot;CreditCard“ table=&quot;CREDIT_CARD&quot;> <key column=&quot;CREDIT_CARD_ID&quot;/> <property name=&quot;number&quot; column=&quot;NUMBER&quot;/> <property name=&quot;expMonth&quot; column=&quot;EXP_MONTH&quot;/> <property name=&quot;expYear&quot; column=&quot;EXP_YEAR&quot;/> </joined-subclass> <joined-subclass name=&quot;BankAccount“ table=&quot;BANK_ACCOUNT&quot;> ... </class> </hibernate-mapping>

22. Demo