Sql error, when i implement join in JAVA code

Question

I have two tables.

First table,

Profession with two columns (profession_id, profession_name) .

Second table,

Applicant with five columns (applicant_id, profession_id, last_name, first_name, entrance_year) .

profession_id in table Applicant and profession_id in table Profession is related fields in MySQL.

I need, instead of profession_id, get a drop-down list of available profession. As, I here implemented using INNER JOIN

This is my class, that working with DB:

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");
        ResultSet resultSet = statement.executeQuery("select a.applicant_id, a.first_name, a.last_name, a.entrance_year, p.profession_name from applicant a join profession p on a.profession_id = p.profession_id");
        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 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();
        }
    }

}

My jsp:

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
  <title></title>
</head>
<body>
<h1>Add applicant</h1>

<form method="post" action="controller?command=saveApplicant">

  <table>
    <tr>
      <th>First Name</th>
      <th>Last Name</th>
      <th>Profession ID</th>
      <th>Entrance Year</th>
    </tr>
  </table>

  <c:choose>
    <c:when test="${applicant ne null}">
      <input type="text" name="first_name" value="${applicant.getFirstName()}"/>
      <input type="text" name="last_name" value="${applicant.getLastName()}"/>
      <input type="text" name="profession_id" value="${applicant.getProfessionId()}"/>
      <input type="text" name="entrance_year" value="${applicant.getEntranceYear()}"/>
      <input type="hidden" name="applicant_id" value="${applicant.getId()}"/>
    </c:when>
    <c:otherwise>
      <input type="text" name="first_name" value=""/>
      <input type="text" name="last_name" value=""/>
      <input type="text" name="profession_id" value=""/>
      <input type="text" name="entrance_year" value=""/>
    </c:otherwise>
  </c:choose>
  <input type=submit value=submit>
</form>
</body>
</html>

I implement that query in database (You can see it in my code):

select a.applicant_id, a.first_name, a.last_name, a.entrance_year, p.profession_name from applicant a join profession p on a.profession_id = p.profession_id

But, when i run my server, and open my jsp, i have error: java.lang.Exception: java.sql.SQLException: Column 'profession_id' not found.

What a mistake I can not understand. What could it be ? Tell me please. Thanks.

Answer 1

EDIT:

In this QUERY,

select a.applicant_id, a.first_name, a.last_name, a.entrance_year, p.profession_name, p.profession_id from applicant a join profession p on a.profession_id = p.profession_id

You only have,

a.applicant_id, a.first_name, a.last_name, a.entrance_year, p.profession_name

There is no p.profession_id

So when you do a,

applicant.setProfessionId(resultSet.getInt("profession_id"));

You get an exception, because you do not have that column in your result list.

ResultSet resultSet = statement.executeQuery("select a.applicant_id, a.first_name, a.last_name, a.entrance_year, p.profession_name, p.profession_id from applicant a join profession p on a.profession_id = p.profession_id");

Answer to your,

i have a class. Applicant.java. in that class, i have professionId with long data type. now my queston. when, i change applicant.setProfessionId(resultSet.getInt("profession_id")) on applicant.setProfessionId(resultSet.getString("profession_name")), i need to change professionId to String data type

You can add a class variable to your Application.java class,

as,

private String professionName;

public String getProfessionName(){
    return professionName;
}


public String setProfessionName(String professionName){
    this.professionName = professionName
}

and have both the,

applicant.setProfessionId(resultSet.getInt("profession_id"));
applicant.setProfessionName(resultSet.getString("profession_name"));

But Still,

If you are trying, I quote,

instead of profession_id, get a drop down list of available profession

You should approach this differently, because this join will only give one profession_name for one application ,

Have a loot at taglib and data binding.

EDIT 2: