Read database object with spring boot and h2 - spring

Question

I want to know how to read database object from h2 database into my spring controller using hibernate (or anything really, I am not married to hibernate).
I have a simple project setup using gradle.
And my application.properties is
spring.thymeleaf.cache=false
# Datasource
spring.datasource.driverClassName=org.h2.Driver
spring.datasource.platform=h2
spring.datasource.url=jdbc:h2:mem:database
spring.datasource.username=something
spring.datasource.password=password
spring.jpa.database-platform=org.hibernate.dialect.H2Dialect
spring.jpa.show-sql=true
# H2
spring.h2.console.enabled=true
spring.h2.console.path=/h2
spring.h2.console.settings.trace=false
spring.h2.console.settings.web-allow-others=false
# Hibernate
spring.jpa.hibernate.ddl-auto=none
spring.jpa.properties.hibernate.show_sql=false
spring.jpa.properties.hibernate.use_sql_comments=false
spring.jpa.properties.hibernate.format_sql=false
spring.jpa.properties.hibernate.current_session_context_class=org.springframework.orm.hibernate4.SpringSessionContext
I can see that schema.sql and data.sql are being executed. And I see my table exists with data inside of it using h2 console. I have an entity object made too.
However I have no idea how I would go about reading my entity object from h2 and into my controller. Can someone point to the right resource or explain how to go about doing it?

Answer 1

By far the simplest approach to this is to use spring-data-jpa. To do this you need an entity (that is, a class with an #javax.persistence.Entity annotation) that will represent a row in your table.
#Entity
public class Thing {
#Id
private String id;
private String name;
}
Then you need a repository that can read and write from the DB. This is an interface that extends one of the spring repository classes, usually CrudRepository, like this:
public interface CustomerRepository extends CrudRepository<Thing, String> {
Thing findById(long id);
}
Then, autowire the repo into your controller's constructor, and you're nearly finished. The last part is calling one of the methods on the repo. You don't have to actually implement the repo, spring will do that for you. The base repo has plenty of useful default methods that you don't even have to list in your code. There are plenty of references for all of this on spring's website and I've linked you to a good tutorial for it (it has gradle examples, but you should really be using maven because it's a lot better in every possible respect).