Выпадающий список реализации с mysql и jdbc

Question

У меня есть две таблицы. Первая таблица Профессия с двумя столбцами (профессия_ид, профессия_имя). Вторая таблица Заявитель с пятью столбцами (имя_искателя, профессия_ид, фамилия, имя_пользователя, имя_доступа). «profession_id» в таблице. Заявитель и «профессия_ид» в таблице. Профессия - это связанные поля в mysql.

CREATE TABLE PROFESSION (
    PROFESSION_ID INT   NOT NULL AUTO_INCREMENT, 
    PROFESSION_NAME VARCHAR(50) NOT NULL, 
    PRIMARY KEY (PROFESSION_ID) 
); 

CREATE TABLE APPLICANT (
    APPLICANT_ID INT   NOT NULL AUTO_INCREMENT, 
    PROFESSION_ID INT   NOT NULL, 
    LAST_NAME  VARCHAR(30) NOT NULL, 
    FIRST_NAME VARCHAR(30) NOT NULL, 
    ENTRANCE_YEAR INT   NOT NULL, 
    PRIMARY KEY (APPLICANT_ID), 
    FOREIGN KEY (PROFESSION_ID) REFERENCES PROFESSION (PROFESSION_ID) 
); 

Это мой класс, который работает с БД:

public enum ApplicantDBProvider { 

    INSTANCE; 

    private Connection connection; 

    private ApplicantDBProvider() { 
     try { 
      Class.forName("com.mysql.jdbc.Driver"); 
      connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/db_applicant", "root", "toor"); 
     } catch (ClassNotFoundException | SQLException e) { 
      System.err.println("Class not found: com.mysql.jdbc.Driver " + e); 
      throw new RuntimeException("Class not found: com.mysql.jdbc.Driver"); 
     } 
    } 

    public Applicant getApplicant(long applicantId) throws Exception { 
     PreparedStatement preparedStatement = null; 
     Applicant applicant = null; 
     try { 
      preparedStatement = connection.prepareStatement("SELECT * FROM applicant WHERE applicant_id=?"); 
      preparedStatement.setInt(1, (int) applicantId); 

      ResultSet resultSet = preparedStatement.executeQuery(); 
      while (resultSet.next()) { 
       applicant = new Applicant(); 
       applicant.setId(resultSet.getInt("applicant_id")); 
       applicant.setFirstName(resultSet.getString("first_name")); 
       applicant.setLastName(resultSet.getString("last_name")); 
       applicant.setProfessionId(resultSet.getInt("profession_id")); 
       applicant.setEntranceYear(resultSet.getInt("entrance_year")); 
      } 
     } catch (SQLException e) { 
      e.printStackTrace(); 
     } finally { 
      if (preparedStatement != null) { 
       preparedStatement.close(); 
      } 
     } 

     return applicant; 
    } 

    public List<Applicant> getApplicants() throws Exception { 
     Statement statement = null; 
     List <Applicant> applicants = new ArrayList<>(); 

     try { 
      statement = connection.createStatement(); 
      ResultSet resultSet = statement.executeQuery("SELECT * FROM applicant"); 
      Applicant applicant = null; 
      while (resultSet.next()) { 
       applicant = new Applicant(); 
       applicant.setId(resultSet.getInt("applicant_id")); 
       applicant.setFirstName(resultSet.getString("first_name")); 
       applicant.setLastName(resultSet.getString("last_name")); 
       applicant.setProfessionId(resultSet.getInt("profession_id")); 
       applicant.setEntranceYear(resultSet.getInt("entrance_year")); 
       applicants.add(applicant); 

      } 

     } catch (SQLException e) { 
      throw new Exception(e); 
     } 

     return applicants; 
    } 

    public void saveApplicant(Applicant applicant) throws Exception { 
     PreparedStatement preparedStatement = null; 

     try { 
      if (applicant.getId() == -1) { 
       preparedStatement = connection.prepareStatement("INSERT INTO applicant (first_name, last_name, profession_id, entrance_year) VALUES (?,?,?,?)"); 

       preparedStatement.setString(1, applicant.getFirstName()); 
       preparedStatement.setString(2, applicant.getLastName()); 
       preparedStatement.setInt(3, (int)applicant.getProfessionId()); 
       preparedStatement.setInt(4, applicant.getEntranceYear()); 

      } else { 
       preparedStatement = connection.prepareStatement("UPDATE applicant SET first_name=?, last_name=?, profession_id=?, entrance_year=? WHERE applicant_id=?"); 

       preparedStatement.setString(1, applicant.getFirstName()); 
       preparedStatement.setString(2, applicant.getLastName()); 
       preparedStatement.setInt(3, (int) applicant.getProfessionId()); 
       preparedStatement.setInt(4, applicant.getEntranceYear()); 
       preparedStatement.setInt(5, (int) applicant.getId()); 
      } 
      preparedStatement.executeUpdate(); 
     } catch (SQLException e) { 
      throw new Exception(e); 
     } finally { 
      if (preparedStatement != null) { 
       preparedStatement.close(); 
      } 
     } 
    } 

    public void deleteApplicant(long applicantId) throws Exception { 
     PreparedStatement preparedStatement = null; 

     try { 
      preparedStatement = connection.prepareStatement("DELETE FROM applicant WHERE applicant_id=?"); 

      preparedStatement.setInt(1, (int) applicantId); 
      preparedStatement.executeUpdate(); 
     } catch (SQLException e) { 
      throw new Exception(e); 
     } finally { 
      if (preparedStatement != null) { 
       preparedStatement.close(); 
      } 
     } 
    } 

    public Profession getProfession(long professionId) throws Exception { 
     PreparedStatement preparedStatement = null; 
     Profession profession = null; 
     try { 
      preparedStatement = connection.prepareStatement("SELECT * FROM profession WHERE profession_id=?"); 
      preparedStatement.setInt(1, (int) professionId); 

      ResultSet resultSet = preparedStatement.executeQuery(); 
      while (resultSet.next()) { 
       profession = new Profession(); 
       profession.setId(resultSet.getInt("profession_id")); 
       profession.setProfessionName(resultSet.getString("profession_name")); 
      } 
     } catch (SQLException e) { 
      e.printStackTrace(); 
     } finally { 
      if (preparedStatement != null) { 
       preparedStatement.close(); 
      } 
     } 

     return profession; 
    } 

    public List<Profession> getProfessions() throws Exception { 
     Statement statement = null; 

     List<Profession> professions = new ArrayList<>(); 
     try { 
      statement = connection.createStatement(); 
      ResultSet resultSet = statement.executeQuery("SELECT * FROM profession"); 
      Profession profession = null; 
      while (resultSet.next()) { 
       profession = new Profession(); 
       profession.setId(resultSet.getInt("profession_id")); 
       profession.setProfessionName(resultSet.getString("profession_name")); 
       professions.add(profession); 
      } 

     } catch (SQLException e) { 
      throw new Exception(e); 
     } finally { 
      if (statement != null) { 
       statement.close(); 
      } 
     } 

     return professions; 
    } 

    public void saveProfession(Profession profession) throws Exception { 
     PreparedStatement preparedStatement = null; 

     try { 
      if (profession.getId() == -1) { 
       preparedStatement = connection.prepareStatement("INSERT INTO profession (profession_name) VALUES (?) "); 

       preparedStatement.setString(1, profession.getProfessionName()); 
      } else { 
       preparedStatement = connection.prepareStatement("UPDATE profession SET profession_name=? WHERE profession_id=?"); 

       preparedStatement.setString(1, profession.getProfessionName()); 
       preparedStatement.setInt(2, (int) profession.getId()); 
      } 
      preparedStatement.executeUpdate(); 
     } catch (SQLException e) { 
      throw new Exception(e); 
     } finally { 
      if (preparedStatement != null) { 
       preparedStatement.close(); 
      } 
     } 

    } 

    public void deleteProfession(long professionId) throws Exception { 
     PreparedStatement preparedStatement = null; 

     try { 
      preparedStatement = connection.prepareStatement("DELETE FROM profession WHERE profession_id=?"); 

      preparedStatement.setInt(1, (int) professionId); 
      preparedStatement.executeUpdate(); 
     } catch (SQLException e) { 
      throw new Exception(e); 
     } finally { 
      if (preparedStatement != null) { 
       preparedStatement.close(); 
      } 
     } 
    } 

Это работает хорошо. Но мне нужно, а не professional_id, получить раскрывающийся список доступных профессий. Я слышу, что реализовано с INNER JOIN. Но как это сделать, я не знаю. Пожалуйста помоги. И мне жаль, что вам нужно прочитать много кода. Благодарю.

Answer 1

Надень выберите в чтении заявителя

OLD:

SELECT * FROM applicant 

NEW: (расширить поля, которые вы хотите прочитать):

[UPDATE: profession.id неправильно, он называет это profession. profession_id здесь]

select a.first_name as applicant_first_name 
    , a.last_name as applicant_last_name, 
    # more applicant ... 
    , p.profession_name 
from applicant a 
inner join profession p on p.profession_id = a.profession_id 
// where ... 

Если у вас есть определенные профессии из-за пределов, просто положить его в where ....