Lab#SB04-1: `JPA` Inherence

Spring Boot JPA Inherence strategies

Spring-Boot

lab

Spring Boot

Author

albertprofe

Published

Tuesday, June 1, 2021

Modified

Sunday, August 10, 2025

Welcome to the cifojava2022-6 wiki!

1 Spring Boot Projects `JPA Inherence` strategies

Name	Type	Description	Link
universalPlanes	Server	Basic Spring Boot Project	Done
JpaInherenceLibrary	Server-Inherence	Inhrence with `JPA` and `UML` @Entity	Done
JpaInherenceLibrary1	Server-Inherence	Inhrence with `JPA` and `UML` MappedSuperClass	Done
JpaInherenceLibrary2	Server-Inherence	Inhrence with `JPA` and `UML` Single Table with Discriminator	Done
JpaInherenceLibrary3	Server-Inherence	Inhrence with `JPA` and `UML` Joined Table	Done
JpaInherenceLibrary4	Server-Inherence	Inhrence with `JPA` and `UML` Table per class	Done

there is no @Service neither @Controller
so, they are basically back-end projects
all work with @CrudRepository

2 Inhrence with `JPA` and `UML`

Inheritance is a fundamental concept of POO, but Relational databases have no concept of inheritance neither NoSQL (MongoDB, DymamoDB), so persisting inheritance in a SQL and NoSQL database _has its own particular way.

Because relational databases have no concept of inheritance, there is no standard way of implementing inheritance in database, so the hardest part of persisting inheritance is choosing how to represent the inheritance in the database.

JPA defines several inheritance mechanisms, mainly defined though the @Inheritance annotation or the <inheritance> element.

There are three inheritance strategies defined from the InheritanceType enum:

SINGLE_TABLE
TABLE_PER_CLASS
JOINED

Single table inheritance is the default with discriminator values,
and table per class is an optional feature of the JPA spec, so not all providers may support it.
in joined strategy each class in the hierarchy is mapped to its table.

MAPPED SUPERCLASS

JPA also defines a mapped superclass concept defined through the @MappedSuperclass annotation or the <mapped-superclass> element.
A mapped superclass is not a persistent class, but allows common mappings to be defined for its subclasses.

Links: orientdb, logicbig, Java Persistence/Inheritance wikibooks and apache

2.1 (0) `@Entity` Inhrence JPA

JpaInherenceLibrary0

Base project:
- POM
- @Entity: Book (SuperClass), ItemBook, RareBook and Auhtor
- n:m : Book<> Auhtor
- DataBase H2: application.properties
- Command Line Runner with methods to test
- @CrudRepository JPA 2.0, @Component (CommandLineRunner) and @Test (Jupiter)
New Topics
- How to code inherence and JPA uses SINGLE_TABLE strategy by default

          @Entity
          public class Book {}


          @Entity(name="BookItem")
          public class ItemBook extends Book {
          
             @ManyToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
             @JoinTable(name = "AUTHOR_BOOK_JOIN_TABLE",
                       joinColumns = { @JoinColumn(name = "AUTHOR_FK" )},
                       inverseJoinColumns = { @JoinColumn(name = "BOOK_FK" )})
             private Set<Author>authors = new HashSet<Author>();
          }

 
          @Entity(name="RareItem")
          public class RareItem extends Book {}


          @Entity(name="Author")
          @Table(name="AUTHOR_TABLE")
          public class Author {}

Versions
- JpaInherenceLibrary v 1.1 : without @MappedSuperClass and @Entity superclass, Single Table strategy is applied BY DEFAULT

2.2 (1) `MappedSuperclass` Inhrence JPA

JpaInherenceLibrary1

Base project:
- POM
- @Entity: ItemBook, RareBook and Auhtor
- Non-@Entity: Book
- DataBase H2: application.properties
- Command Line Runner with methods to test
- @CrudRepository JPA 2.0, @Component (CommandLineRunner) and @Test (Jupiter)
New Topics
- How can not we code @MappedSuperclass and @ManyToMany author

          @MappedSuperclass
          public abstract class Book {}


          @Entity(name="BookItem")
          @Table(name="ITEM_BOOK_TABLE")
          public class ItemBook extends Book {
          
             @ManyToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
             @JoinTable(name = "AUTHOR_BOOK_JOIN_TABLE",
                         joinColumns = { @JoinColumn(name = "AUTHOR_FK" )},
                         inverseJoinColumns = { @JoinColumn(name = "BOOK_FK" )})
             private Set<Author>authors = new HashSet<Author>();
          }

 
          @Entity(name="RareItem")
          @Table(name="RARE_ITEM_TABLE")
          public class RareItem extends Book {}


          @Entity(name="Author")
          @Table(name="AUTHOR_TABLE")
          public class Author {}

With @MappedSuperclass any relationship can’t be done

With @MappedSuperclass
With @MappedSuperclass, one SuperClass and two SubClasses:

With @MappedSuperclass
Versions
- JpaInherenceLibrary1 v 1.0 : not using author just inherence without relatonship @ManyToMany

2.3 (2) `Single Table with Discriminator` Inhrence JPA

JpaInherenceLibrary2

Base project:
- POM
- @Entity: Book (SuperClass), ItemBook, RareBook and Auhtor
- n:m : Book<> Auhtor
- DataBase H2 : application.properties
- Command Line Runner with methods to test
- @CrudRepository JPA 2.0, @Component (CommandLineRunner) and @Test (Jupiter)
New Topics
- How to code @Inheritance(strategy = InheritanceType.SINGLE_TABLE)

           @Entity
           @Inheritance(strategy = InheritanceType.SINGLE_TABLE)
           @DiscriminatorColumn(name="BOOK_TYPE", 
                 discriminatorType = DiscriminatorType.STRING)
           public class Book {}


          @Entity(name="BookItem")
          @Table(name="BOOK_ITEM_TABLE")
          @DiscriminatorValue(value= "ITEMBOOK")
          public class BookItem extends Book {
          
          @ManyToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
          @JoinTable(name = "AUTHOR_BOOK_JOIN_TABLE",
                 joinColumns = { @JoinColumn(name = "AUTHOR_FK" )},
                 inverseJoinColumns = { @JoinColumn(name = "BOOK_FK" )})
          private Set<Author>authors = new HashSet<Author>();}
 

          @Entity(name="RareItem")
          @Table(name="RARE_ITEM_TABLE")
          @DiscriminatorValue(value= "REAREBOOK")
          public class RareItem extends Book {}


          @Entity(name="Author")
          @Table(name="AUTHOR_TABLE")
          public class Author {}

With @Inheritance and SINGLE_TABLE

![@Inheritance ]( https://drive.google.com/uc?id=18nfiKnQaim4-lTD21iBwy313Daxtv73H)

version 1.1 : JpaInherenceLibrary2, SINGLE_TABLE strategy

2.4 (3) `Joined Table` Inhrence JPA

JpaInherenceLibrary3

Base project:
- POM
- @Entity: Book (SuperClass), ItemBook, RareBook and Auhtor
- n:m : Book<> Auhtor
- DataBase H2 : application.properties
- Command Line Runner with methods to test
- @CrudRepository JPA 2.0, @Component (CommandLineRunner) and @Test (Jupiter)
New Topics
- How to code @Inheritance(strategy = InheritanceType.JOINED)

          @Entity
          @Table(name="BOOK_TABLE")
          @Inheritance(strategy = InheritanceType.JOINED)
          @DiscriminatorColumn(name="BOOK_TYPE",
                 discriminatorType = DiscriminatorType.STRING)
          public class Book {}


          @Entity(name="BookItem")
          @Table(name="BOOK_ITEM_TABLE")
          @PrimaryKeyJoinColumn(name = "bookItemId")
          @DiscriminatorValue(value= "ITEMBOOK")
          public class BookItem extends Book {
          
          @ManyToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
          @JoinTable(name = "AUTHOR_BOOK_JOIN_TABLE",
                 joinColumns = { @JoinColumn(name = "AUTHOR_FK" )},
                 inverseJoinColumns = { @JoinColumn(name = "BOOK_FK" )})
          private Set<Author>authors = new HashSet<Author>();}
 

          @Entity(name="RareItem")
          @Table(name="RARE_ITEM_TABLE")
          @PrimaryKeyJoinColumn(name = "rareItemId")
          @DiscriminatorValue(value= "RAREBOOK")
          public class RareItem extends Book {}


          @Entity(name="Author")
          @Table(name="AUTHOR_TABLE")
          public class Author {}

With @Inheritance and JOINED

![@Inheritance JOINED](https://drive.google.com/uc?id=1BpxaW7fV_kh4PyFWn3i49nG4SqnKYpAE)

verison 1.1 : JpaInherenceLibrary3

2.5 (4) `Table per class` Inhrence JPA

JpaInherenceLibrary4

Base project:
- POM
- @Entity: Book (SuperClass), ItemBook, RareBook and Auhtor
- n:m : Book<> Auhtor
- DataBase H2 : application.properties
- Command Line Runner with methods to test
- @CrudRepository JPA 2.0, @Component (CommandLineRunner) and @Test (Jupiter)
New Topics
- How to code @Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)


          @Entity
          @Table(name="BOOK_TABLE")
          @Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
          public class Book {}


          @Entity(name="BookItem")
          @Table(name="BOOK_ITEM_TABLE")
          public class BookItem extends Book {
          
          @ManyToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
          @JoinTable(name = "AUTHOR_BOOK_JOIN_TABLE",
               joinColumns = { @JoinColumn(name = "AUTHOR_FK" )},
               inverseJoinColumns = { @JoinColumn(name = "BOOK_FK" )})
          private Set<Author>authors = new HashSet<Author>();}
 

          @Entity(name="RareItem")
          @Table(name="RARE_ITEM_TABLE")
          public class RareItem extends Book {}


          @Entity(name="Author")
          @Table(name="AUTHOR_TABLE")
          public class Author {}

With @Inheritance and TABLE_PER_CLASS

version 1.1 : JpaInherenceLibrary4

2.6 (0) Basic Spring Boot project

Universal Planes

Preliminary works:
- Create project on Spring Init
version 1.0 : spring boot executions

1 Spring Boot Projects JPA Inherence strategies

2 Inhrence with JPA and UML

2.1 (0) @Entity Inhrence JPA

2.2 (1) MappedSuperclass Inhrence JPA

2.3 (2) Single Table with Discriminator Inhrence JPA

2.4 (3) Joined Table Inhrence JPA

2.5 (4) Table per class Inhrence JPA