Java Spring Boot - JPA - Hibernate - H2 - Entities Inheritance Mapping - Joined Table Strategy

In the first place we will configure database connection. Later we will learn how to use inheritance together with JPA and Hibernate in Java Spring Boot application. We will create abstract super class (parent class) and then two sub-classes (child classes) which will inherit all of the properties and mapping information from parent class. We will use @Inheritance annotation to specify strategy which we will use. This time it will be JOINED strategy. In our super class we will also use @Enumerated annotation to learn how to persist enums. In the final stage we will learn how to use inheritance in case of repositories which we will use to persist and delete our entities from the database. We will track everything using H2 web console. Keep coding!
Joined table source code: github.com/codeforgeyt/jpa-in...
Joined table video: • Java Spring Boot - JPA...
Single table source code: github.com/codeforgeyt/jpa-in...
Single table video: • Java Spring Boot - JPA...
Superclass source code: github.com/codeforgeyt/jpa-in...
Superclass video: • Java Spring Boot - JPA...
Table per class source code: github.com/codeforgeyt/jpa-in...
Table per class video: • Java Spring Boot - JPA...
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[@ranaisrivastav363]

This video saved me SOOOO much trouble. This video was a godsend. Thank you so much!

[@CodeForgeYT]

Awesome! Glad to hear that!

[@GolFoxtrotAlpha]

That was perfect. Thank you so much!

[@CodeForgeYT]

Glad it helped!

[@OFaruk58]

Dude very nice and clear video!

[@CodeForgeYT]

Hey! Thanks! I am glad you like it!

[@deepusasidharan2012]

Super good explanations!!!

[@jahadulrakib9928]

Best Video List about Spring Boot ever i seen yet

[@CodeForgeYT]

Wow! Big thanks! I really appreciate it!

[@jahadulrakib9928]

@@CodeForgeYT sir, can you please make a complete Microservice video list using Spring boot?

[@CodeForgeYT]

@@jahadulrakib9928 You mean a playlist with existing videos about microservices using Spring Boot?

[@jahadulrakib9928]

@@CodeForgeYT sir, i want to learn microservice with CQRS and Event Sourcing implementation. you can make a new video series about this topic.

[@mauronunes7196]

still kicking in 2023, awesome

[@user-fj2dd2jx8d]

It is so good explanation. Thank you for saving my time. I have one question, if I want to update knight to archer, what should I do? I tried creating new archer instance with old knight's primary key. Then I request save for updating, but new archer was created with ignoring old knight's primary key.

[@CodeForgeYT]

Well conversion between types is topic for separated video

[@deepakrohilla5574]

Hi, I have to implement similar case. In my Order class, I have list of Product class objects. Where Product is the base Entity with some common properties and Book and Apparel is the child class Entity which extends the Product class. Now while saving the Order using REST service and sending the list of products in JSON format, data is not getting saved in Book and Apparel table. Data is saved only in base table entity means in Product table only. pls help me. let me know how can i share my code snippet?

[@msea5654]

i have a question : does the child class inherit associations defined in the parent class ( meaning if the parent have a relationship with another class like one to many or many to many ) does it apply on the child class ?

[@CodeForgeYT]

I think so, try it out!

[@msea5654]

@@CodeForgeYT i will but if you noticed i asked question , i was hoping to get more in depth info anyway good luck with detailed examples .

[@GolFoxtrotAlpha]

For example, I just want to find all Archerys from repository. How can I do that? My repository extends InfantryRepository and both has a method which name is findAll().

[@CodeForgeYT]

Well calling Iterable infantries = archerRepository.findAll() should do the work and find archers

[@giovanni.n]

So when you select from Infantry how do you know if it's a knight or archer? Do you have to use instanceof?

[@CodeForgeYT]

Hi! If you want to get e.g. archer data from db, you have to use archer repository. You know that you will get archers if you will use ArcherRepository so you don't have to use instanceof. Keep coding!

[@giovanni.n]

@@CodeForgeYT that of course if i know which type i want. But imagine for example i have a class Squad which has a member field of type Infantry. If I'm loading Squad from db using it's PK. How do i know which subtype the Infantry attribute is holding?

[@giovanni.n]

It's more of a question about polymorphism than it is about JPA mapping

[@CodeForgeYT]

@@giovanni.n Well it is determined when it is being saved to the db. Spring knows the type of object because it is saved in the specific table. Spring is smart enough to resolve entities when it is getting data back from db. It will create required object to put it as the reference to your Squad instance. You can experiment with it and share the results.

[@giovanni.n]

@@CodeForgeYT yes i think you're right Spring will instantiate it with the correct subtype based on what it found in the db. But for us to know which subtype to cast to in the code without getting ClassCastException error we need to use instanceof first. Or maybe I'm missing something?

[@muratalikistan548]

Thanks for this video .I tried this. it is works perfect but i want to ask you something. For example now infantry id=2 . if we have another entity classes different from this , its id is starting from 3 not 1. How we can fix this problem?

[@CodeForgeYT]

You have to change the strategy of generting ids for primary keys. For example you can define separated sequence for each entity. Hope it helps, keep coding!

[@muratalikistan548]

@@CodeForgeYT Yess Thanks bro. SequenceGenerator fixed this problem. Thank you so much.

[@CodeForgeYT]

@@muratalikistan548 You are welcome!

[@mossabseifelislemdehane2849]

Great explanations but how can I retrieve all infantry

[@user-jq6pz1xh6h]

Can you help me please . I have almost the same relation between classes, except abstract parent: @Entity Class A; @Entity Class B extends A; And method (A a){ repoA.save(a); B b = new B(); repoB.save(b); } And I get double records in table A and one record in table B. How I can avoid double in A?

[@CodeForgeYT]

What you mean by double record? You are creating two different entities and persisting them. Since those are two different entities you get two records in table for class A.

[@djamalabdounassirharoun5878]

Hi ! I just came across your tutorial, good job, everything is clear. On the other hand, my problem is with the save function, there you have saved the data manually, what to do if the data comes from a client server like PostMan Sorry for my English, I translate on google translate , Thank's !

[@CodeForgeYT]

Hi! You do exactly the same. I have created video where we are implementing one to many web service there is no inheritance but it can be helpful for you. You can check it out, I bet it will answer your questions. Keep Coding!

[@djamalabdounassirharoun5878]

@@CodeForgeYT Thank you for your reply ! Which video is in your channel ?

[@CodeForgeYT]

@@djamalabdounassirharoun5878 It is in spring playlist, video is called: Java Spring Boot - JPA - Hibernate - H2 - One To Many - REST Web Service - RESTful API

[@djamalabdounassirharoun5878]

@@CodeForgeYT Thank's !

[@djamalabdounassirharoun5878]

@@CodeForgeYT Unfortunately that doesn't help me. In fact my problem is that with the Joined inheritance strategy, the attributes are zero when I do the POST to save.

[@pescoder7486]

How can you add a infantry object to infantry table???

[@muaztastemel538]

How do you use it with spring controller and sevice?

[@CodeForgeYT]

You can inject depenedency of repository to service. Then you can simply call different methods from repository in your service depending on your business logic

[@muaztastemel538]

CodeForgeYT i mean, for example every entity have different service and there are one service interface so we should these services inject to a main service. May be it should be at complie time.Coz detecting injection problems at complie time is better than run time. So we need to inject services which have same abstraction to a main service (maybe creating hashmap in a configure class). Do you have any example or link about that?

[@CodeForgeYT]

@@muaztastemel538 Hi, sorry but I don't have any example for such use case. For sure it is worth to expermient with approach you have described!

[@alissonnunes5318]

I know I am missing the point, but I could not avoid to say that knight is not a type of infantry.

[@CodeForgeYT]

Isn't it a type of heavy medival infantry?

[@user-xi5vv3pg6o]

why it is CrudRepo and not JpaRepo ?

[@hieuvuduc8840]

Bad example What different between ArcherRepository and KnightRepository ? Only name ? The truth is you can use KnightRepository to create both archer and knight. Why you have to create two repository ?