JPA : One to Many Mapping using Hibernate Spring Boot

STEP 1 :: Add the dependencies

You need to add the following dependencies in your build.gradle file.

    
    compile('org.springframework.boot:spring-boot-starter-data-jpa')
    compile('org.springframework.boot:spring-boot-starter-jdbc')
    runtime('mysql:mysql-connector-java')

STEP 2 :: Make Entity classes

You need to create two entity QUESTION and TOPIC.

Here the Topic Entity will have an annotation @OneToMany , this indicates the following

• This one topic can have many questions.
• All the questions will be deleted or updated when topic is deleted/updated.
• Its mapping is defined by Entity Question by the mapping of topic variable.
• It will give a list of all question of a topic when it is fetched
• If you do not need questions when topic is fetched then make fetch type as LAZY

    @OneToMany(cascade = CascadeType.ALL,mappedBy = "topic",fetch = FetchType.EAGER)
    private List questions;

Here the Question entity will have the annotation @ManyToOne, this will indicate the following,

• One question can belong to only one topic.
• When you fetch question, it will not fetch the topic because the fetch mode is LAZY
• It will join make the foreign key column as topic_id. If you want any other name, then you can define using @JoinColumn annotation

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "topic_id")
    private Topic topic;

Full class code is shown below