There are three basic entity relationships:-
- One-to-One
- One-to-Many/Many-to-one
- Many-to-Many
A Single post can have multiple comments by this way we can apply one-to-many Mapping
Installation
Clone the repo from here:- Click here
Import Maven based project in any of your Favourite IDE.
./mvnw spring-boot:run
Output
Open in Browser
Access H2 Database.
http://localhost:8080/h2-console
Usage
MainClass.java
run() method is run when the application is started. The data is added in the database.
Post post = new Post("Spring Boot Post Title","Spring Boot Post Description");
Comment comment1 = new Comment("Thanks for uploading");
Comment comment2 = new Comment("Comment2 test");
Comment comment3 = new Comment("Comment3 test");
post.getComments().add(comment1);
post.getComments().add(comment2);
post.getComments().add(comment3);
postRepository.save(post);
Post.java
Id column is used to map the post and comments together.
@OneToMany(cascade = CascadeType.ALL)
@JoinColumn(name = "post_Comment_id",referencedColumnName = "id")
List<Comment> comments = new ArrayList<>();
Output
Comments are mapped by the ID of the Post on which they are commented. As you can see in the below images.
Configuration
application.properties
spring.jpa.show-sql = true
# Enabling H2 Console
spring.datasource.url=jdbc:h2:mem:testdb
spring.jpa.defer-datasource-initialization=true
spring.h2.console.enabled=true
# Enable Web Access
spring.h2.console.settings.web-allow-others=true
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