Entity Mapping

package com.example.domain;

import jakarta.persistence.*;

@Entity
@Table(name = "t_account")
public class Account {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long accountId;

    @Column(nullable = false, unique = true)
    private String login;

    @Column(nullable = false)
    private String mail;

    protected Account() {}

    public Account(String login, String mail) {
        this.login = login;
        this.mail = mail;
    }

    public Long getAccountId() { return accountId; }
    public String getLogin()   { return login; }
    public String getMail()    { return mail; }
}

Rpeository Delcaration

package com.example.persistence;

import com.example.domain.Account;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.query.Param;

import java.util.Optional;

public interface AccountRepository extends JpaRepository<Account, Long> {
    Optional<Account> findByLogin(String login);

    @Query("select a from Account a where a.mail = :email")
    Optional<Account> locateByEmail(@Param("email") String email);
}

Service Layer

package com.example.application;

import com.example.domain.Account;
import com.example.persistence.AccountRepository;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

import java.util.List;

@Service
@Transactional
public class AccountManager {
    private final AccountRepository repo;

    public AccountManager(AccountRepository repo) {
        this.repo = repo;
    }

    public List<Account> fetchAll() {
        return repo.findAll();
    }

    public Account fetchByLogin(String login) {
        return repo.findByLogin(login)
                   .orElseThrow(() -> new IllegalArgumentException("Account not found"));
    }

    public Account register(Account account) {
        return repo.save(account);
    }

    public void remove(Long id) {
        repo.deleteById(id);
    }
}

Application Configuration

spring:
  datasource:
    url: jdbc:postgresql://localhost:5432/sampledb
    username: app
    password: secret
  jpa:
    hibernate:
      ddl-auto: validate
    properties:
      hibernate:
        format_sql: true