Creating Post Entity and Many to One Relationship with User Entity
In this section, we will create a Post entity that contains many to one relationship with the User entity.
Step 1: Create a class with the name Post.java in the package com.javatpoint.server.main.user.
Step 2: Post.java is an entity, so we need to add @Entity annotation.
Step 3: Add three fields: id, description, and user.
Step 4: Generate Getters and Setters.
Step 5: Generate toString().
Remember: Uncheck the user during the generation of toString().
Step 6: A user can do many posts, so add @ManyToOne annotation. The User entity has many to one relationship with the Post entity. The fetch type will not retrieve the details of the user unless we called Post.getUser.
Step 7: Id is a primary key, so we need to add @Id annotation.
We have configured the relationship on the side of Post entity. Now we are required to configure relationship on the side of User entity.
A user can make a list of posts, so the post has one-to-many relationships.
Step 8: Open User.java file and create a list of posts.
Step 9: Add an annotation @OneToMany with property (mappedBy="user"). It will create a relationship column in the Post entity.
Step 10: Generate Getters and Setters.
Step 11: Restart the application.
We can see in the log that there are two tables post and user. The Post table has a link to the User table by a user id. A user can have multiple posts, and all of them have the same user id.
Step 12: Now, open the H2 Console. We can see that are two tables named USER and POST.
Step 13: Open the data.sql file that we have created earlier and insert the data into POST table. We have inserted the following data:
Step 14: Restart the application.
Step 15: Restart the H2 Console and execute the query SELECT *FROM POST;
It shows the data which we have inserted into the data.sql file.