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Java Spring MVC & Spring Boot (Write API with Spring Boot Application)…

- - - - Database <=> Models
        Properties with anotations
        
        Entity
        public class User {
        ...private Id GeneratedValue Long id;
        //getter, setter
    - - public interface UserRepository extends JpaRepository<User, Long> {...}
        
        Initialize data
        (Code First)
        
        Configuration
        public class Database {
        Bean
        CommandLineRunner initDatabase(UserRepository repository){
        //creates object and implements interface CommandLineRunner ...
        
        Find with "try-catch":
        repository.findById(id)
        .orElseThrow(() -> new Exception("Cannot find user"));
        
        Insert:
        repository.save(newUser)
        
        Update:
        repository.findById(id)
        .map(user -> {
        user.setEmail(newUser.getEmail());//...
        }).orElseGet(() -> {
        newUser.setId(id);
        });
        
        Delete
        repository.deleteById(id);
    - - RestController
        public class UserController {...}
        //Dependency Injection:
        private final UserRepository repository;
        public UserController(UserRepository repository) {...}
        
        Rest methods: GET, POST, PUT, DELETE
        
        GET method
        
        get method with route:
        GetMapping("/users/{id}")
        User findById(@PathVariable Long id) {...}
        
        POST, PUT, DELETE
        
        POST method:
        PostMapping("/registerUser")
        User registerUser(@RequestBody User newUser) {...}
        //Postman => Body, Raw, JSON
        
        PUT method:
        PutMapping("/users/{id}")
        User updateUser(@RequestBody User newUser, PathVariable Long id) {...}
        
        DELETE method:
        DeleteMapping("/users/{id}")
        void deleteEmployee(@PathVariable Long id) {...}