joplin-notes/joplin notion extension/Web Development/Java/Spring/Extras Telusko.md

Extras telusko

• for configuring h2 database(in memory database)
  • make sure package is there in pom.xml
  • add following in application.properties

    spring.h2.console.enabled=true
    spring.datasource.platform=h2
    spring.datasource.url=jdbc:h2:mem:telusko
    

    here telusko is name of database
  • now start your application and go to localhost:8080/h2~console and u will get a login page. now click on test connection button
• for configuring JPA
  • make sure respective dependency is there and at application.properties along with spring.datasource properties one more is mentioned for say mysql spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.MySQLDialect
  • in POJO add annotation Entity above class defintion and in instance say aid add @Id annotation
  • now a table with fields of those POJO instance name will be created
  • u can add data.sql in src/main/resources to add initial data
  • in order to do crud operations use CrudRepository which is a part of spring data commons which is part of JPA
  • Create this interface

   package com.example.demo;
  
   import org.springframework.data.repository.CrudRepository;
  
   public interface AlienRepo extends CrudRepository<Other,Integer> {
  
  
   } 
  
  

  and then in your main file/controller to save data use

  public class HomeController(){
  	@Autowire
  	Alienrepo repo;
  
  	 @RequestMapping("/addAlien")
  	public String addAlien(Alien alien){ 
  		repo.save(alien);
  		return "home";
  	}
  
  	@RequestMapping("/getAlien")
  	public ModelAndView getAlien(@RequestParam int aid){ 
  		ModelAndView mv= new ModelAndView("showAlien");
  		Alien alien=repo.findById(aid).orElse(new Alien());
  		mv.addObject(alien);
  		return mv;
  	}
  }
  

• More query methods for interface Repo
  • In the following code, these other query methods are defined by just declaring then by following certain conventions like findBy<PropertyName><Operation> here property like Tech,Aid(first letter must be capital and other as small)
  • everything is not configured with conventions so for complex queries Query annotation have to be used. ?1 is used instead of ? bcz there can be other placeholders too and its to index them.

     package com.example.demo;
  
     import org.springframework.data.repository.CrudRepository;
  
     public interface AlienRepo extends CrudRepository<Other,Integer> {
  
    	List<Alien> findByTech(String tech);
  
    	 List<Alien> findByAidGreaterThan(int aid);
  
    	 // jpql instead of sql
    	 @Query("from Alien where tech=?1 order by aname")
    	 List<Alien> findByTechSorted(String tech);
     }