Example to show JPA demo
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JPARepository extends CRUDRepository and PagingAndSortingRepository. SO JPARepository has some extra methods.
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@Entity class should always implement Serializable.
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Instead of autowiring at instance var level, use @autowired at the same class constructor.
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We use @Id annotation for making a field a Primary key, similarly we can use @EmbeddedId to use a composite primary key. Suppose, we have to use fields "id" and "dob" as a ID. So, create a Corresponding class with @Embeddable annotation having id and dob as fields and use this classname as one of the field in your entity class and use @EmbeddedId in your entity class at this corresponding classname variable.
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IN reources folder, add schema.sql with queries to create a table. add data.sql to add data to tables. Finally, In application.properties, add spring.jpa.hibernate.ddl-auto=none
With these 3 things, spring will create and add data and we dont have to do anything else.
Note: When data is added to tables and some String in db should map to Enum type in @Entity class. then, we need a converter at compile time. So create a class implementing AttributeConverter and override its uniplemented methods to solve this problem. The class should be annotated with @Converter(autoApply=true)