I have the following function and I am trying to compare the number of students enrolled in a class with the class max. If the number enrolled is greater than the class max, I want to return a message that says, "The Class if Full".
public static void classFullCheck() {
try {
String currentNumberInClassAsString = ("SELECT class_id, COUNT(*) FROM ClassSelector.student_x_class WHERE class_id = " + selectedClass);
rs = myStmt.executeQuery(currentNumberInClassAsString);
int currentNumberInClassAsInt = 0;
if(rs.next()){
currentNumberInClassAsInt = rs.getInt(1);
}
String classSizeAsString = ("SELECT class_size FROM ClassSelector.classes WHERE class_id = " + selectedClass);
rs = myStmt.executeQuery(classSizeAsString);
int classSizeAsInt = 0;
if(rs.next()){
classSizeAsInt = rs.getInt("class_size");
}
if (currentNumberInClassAsInt > classSizeAsInt){
System.out.println("Sorry, this class is Full!");
}
} catch (java.sql.SQLException SQL) {
SQL.printStackTrace();
}
}
I am inserting the classFullcheck() function into the addClass() function like this:
public static void addClass() {
try {
rs = myStmt.executeQuery("SELECT * FROM ClassSelector.classes");
while (rs.next()) {
String availableClasses = rs.getString("class_id") + "\t" + rs.getString("class_name") + "\t" + rs.getString("description");
System.out.println(availableClasses);
}
System.out.println("Enter Class ID from Classes Listed Above to Join: ");
selectedClass = sc.nextLine();
rs = myStmt.executeQuery("SELECT * FROM ClassSelector.classes WHERE class_id = " + selectedClass);
while (rs.next()) {
classFullCheck();
String innerJoin = (userEnterIdAsName + " has been added to " + rs.getString("class_name") + " " + rs.getString("class_id"));
System.out.println(innerJoin);
String student_x_classJoin = "INSERT INTO student_x_class" + "(student_id, student_name, class_id, class_name)" + "VALUES (?, ?, ?, ?)";
PreparedStatement pStmt = con.prepareStatement(student_x_classJoin);
pStmt.setString(1, user_entered_student_id);
pStmt.setString(2, userEnterIdAsName);
pStmt.setString(3, rs.getString("class_id"));
pStmt.setString(4, rs.getString("class_name"));
pStmt.executeUpdate();
System.out.println("Would you like to enroll " + userEnterIdAsName + " into another class? (Y/N)");
String addAdditionalClass = sc.nextLine();
if (addAdditionalClass.equalsIgnoreCase("Y")) {
addClass();
} else if (addAdditionalClass.equalsIgnoreCase("N")) {
return;
}
}
}
catch (java.sql.SQLException SQL) {
System.out.println("Wait, This Student is already enrolled in this class!");
}
}
I am currently just getting both messages printed out, even if a class is not full. Any suggestions would help a lot.
if (currentNumberInClassAsInt >= classSizeAsInt) {
String updateStatus = "Update ClassSelector.classes SET status = ? WHERE class_id = " + selectedClass;
PreparedStatement pStmt = con.prepareStatement(updateStatus);
pStmt.setString(1, "Closed");
pStmt.executeUpdate();
System.out.println("Sorry, this class is Full! Select a different Class:");
System.out.println("\nSign Up For a Class\n");
addClass();
}
I think you want this:
currentNumberInClassAsInt = rs.getInt(2);
instead of:
currentNumberInClassAsInt = rs.getInt(**1**);
I don't think the ResultSet is 0 based...
Also is rs a global variable because it looks like you are changing your ResultSet rs when you call classFullCheck(). You may not have what you think you do in the ResultSet...
rs = myStmt.executeQuery("SELECT * FROM ClassSelector.classes WHERE class_id = " + selectedClass);
while (rs.next()) {
classFullCheck();//****************result set changed here******************
String innerJoin = (userEnterIdAsName + " has been added to " + rs.getString("class_name") + " " + rs.getString("class_id"));
You may think you have this: rs = myStmt.executeQuery("SELECT * FROM ClassSelector.classes WHERE class_id = " + selectedClass); in your result set but you change rs in classFullCheck(). You may want to store the data in a different object that way when you run another query you can still access the data.
Related
In method save() I receive as input an instance of Employee, and I want to add it to the table employee and return this added instance. I read about this problem but I didn't find an answer to my problem.
public Employee save(Employee employee) throws SQLException {
Connection connection = ConnectionSource.instance().createConnection();
String sql = "insert into employee VALUES(" +employee.getId() + ", " + "'employee.getFullName().getFirstName()'" + ", " +"'employee.getFullName().getLastName()'"+ ", " +"'employee.getFullName().getMiddleName()'"+ ", " + "'employee.getPosition()'" + ", " +"'employee.getHired()'"+ ", " + employee.getSalary()+ ", " +employee.getManagerId()+ ", " +employee.getDepartmentId() + ")";
connection.prepareStatement(sql);
PreparedStatement ps2 = connection.prepareStatement("select * from employee");
ResultSet resultSet = ps2.executeQuery();
resultSet.next();
Employee emp = new Employee(... );
return emp;
}
First of all, better not use such approach:
String sql = "insert into employee VALUES(" +employee.getId() + ", " + "'employee.getFullName().getFirstName()'" + ", " +"'employee.getFullName().getLastName()'"+ ", " +"'employee.getFullName().getMiddleName()'"+ ", " + "'employee.getPosition()'" + ", " +"'employee.getHired()'"+ ", " + employee.getSalary()+ ", " +employee.getManagerId()+ ", " +employee.getDepartmentId() + ")";
you can have an sql injection in that case.
Instead use
String sql = "insert into employee values (?, ?, ...)";
PreparedStatement statement = conn.prepareStatement(sql);
statement.setInt(1, employee.getId());
statement.setString(2, employee.getFullName().getFirstName());
...
For your problem you can try something like this:
public Employee save(Employee employee) throws SQLException {
try (Connection connection = ConnectionSource.instance().createConnection();;
PreparedStatement statement = connection.prepareStatement(SQL_INSERT,Statement.RETURN_GENERATED_KEYS);) {
statement.setInt(1, employee.getId());
statement.setString(2, employee.getFullName().getFirstName());
// ...
int affectedRows = statement.executeUpdate();
if (affectedRows == 0) {
throw new SQLException("Creating employee failed, no rows affected.");
}
try (ResultSet generatedKeys = statement.getGeneratedKeys()) {
if (generatedKeys.next()) {
employe.setId(generatedKeys.getLong(1));
}
else {
throw new SQLException("Creating employe failed, no ID obtained.");
}
}
return employee;
}
}
Everything just worked don't know what I did ,but I keep getting the error when wanting to UPDATE information in my SQL database. Error : The column position '1' is out of range. The number of columns for this ResultSet is '0'
try
{
String em = EmailField.getText();
String na = NameField.getText();
String su = SurnameField.getText();
String i = IDField.getText();
String ce = CellField.getText();
String query2 = "UPDATE LouwDataBase.Table1Test "
+ "SET Email = "+"'"+em+"'"+" , "
+ "Name = "+"'"+na+"'"+" , "
+ "Surname = "+"'"+su+"'"+" , "
+ "ID = "+"'"+i+"'"+" , "
+ "Cell = "+"'"+ce+"'"
+ " WHERE Email = "+"'"+UserEmailID+"'";
conn = DriverManager.getConnection("jdbc:derby://localhost:1527/MyDataBase", "LouwDataBase", "1234");
stat = conn.createStatement();
try (Connection conn = this.connect();
PreparedStatement pstmt = conn.prepareStatement(query2))
{
pstmt.setString(1, em);
pstmt.setString(3, na);
pstmt.setString(4, su);
pstmt.setString(5, i);
pstmt.setString(6, ce);
pstmt.executeUpdate();
}
catch (SQLException e)
{
System.out.println(e.getMessage());
}
}
Since you're using PreparedStatement, I think you need to have question marks in the query and then use pstmt.setString().
try {
String em = EmailField.getText();
String na = NameField.getText();
String su = SurnameField.getText();
String i = IDField.getText();
String ce = CellField.getText();
String query2 = "UPDATE LouwDataBase.Table1Test "
+ "SET Email = ?, "
+ "Name = ?, "
+ "Surname = ?, "
+ "ID = ?, "
+ "Cell = ?"
+ " WHERE Email = ?";
conn = DriverManager.getConnection("jdbc:derby://localhost:1527/MyDataBase", "LouwDataBase", "1234");
stat = conn.createStatement();
try (Connection conn = this.connect();
PreparedStatement pstmt = conn.prepareStatement(query2)) {
pstmt.setString(1, em);
pstmt.setString(3, na);
pstmt.setString(4, su);
pstmt.setString(5, i);
pstmt.setString(6, ce);
pstmt.executeUpdate();
}
catch (SQLException e) {
System.out.println(e.getMessage());
}
}
In this code:
public static void viewTable(Connection con, String dbName)
throws SQLException {
Statement stmt = null;
String query =
"select COF_NAME, SUP_ID, PRICE, " +
"SALES, TOTAL " +
"from " + dbName + ".COFFEES";
try {
stmt = con.createStatement();
ResultSet rs = stmt.executeQuery(query);
while (rs.next()) {
String coffeeName = rs.getString("COF_NAME");
int supplierID = rs.getInt("SUP_ID");
float price = rs.getFloat("PRICE");
int sales = rs.getInt("SALES");
int total = rs.getInt("TOTAL");
System.out.println(coffeeName + "\t" + supplierID +
"\t" + price + "\t" + sales +
"\t" + total);
}
} catch (SQLException e ) {
JDBCTutorialUtilities.printSQLException(e);
} finally {
if (stmt != null) { stmt.close(); }
}
}
In particular, this code:
ResultSet rs = stmt.executeQuery(query);
Does this statement retrieve all rows to ResultSet, or partly? I need to load a table with 5 million rows in Hibernate and there is an OutofMemory error. It fails on this line:
List<Term> terms = em.createQuery(criteria).getResultList();
I need to find a way in Mysql & Hibernate to load this table with a memory issue. Thanks.
I am trying to develop a simple Java DVD library console app in Java. I have created a database table that contains a list of DVD's. I have managed to get the adding a new DVD to the database functionally working, but I am struggling to delete a row from the database. When I use a SQL statement to select a row (row 7) then run the line 'rs.delete' I get the following exception:-
Invalid cursor state - no current row.
Below is my database table:-
ID Film Name Genre Rating
-------------------------------
1 Robocop Sci-fi 18
2 Terminator Sci-fi 18
3 Alien Sci-fi 18
4 Big Fish Fantasy PG
5 The Pianist Drama 18
6 Total Recall Sci-fi 18
7 Carnage Comedy 18
Below is copy of my code. Please could somebody help?
/*
* To change this license header, choose License Headers in Project Properties.
* To change this template file, choose Tools | Templates
* and open the template in the editor.
*/
package dvdlibrary;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;
import java.sql.ResultSet;
import javax.swing.JOptionPane;
import java.util.Scanner;
/**
*
* #author Andy
*/
public class DVDLibrary {
Connection con;
Statement stmt;
ResultSet rs;
String selection = "";
int id_num =0;
String film_name ="";
String genre ="";
String rating="";
public DVDLibrary()
{
DoConnect();
}
public void DoConnect() {
try
{
String host = "jdbc:derby://localhost:1527/DVDLibrary";
String username = "andyshort";
String password = "Pa55word";`enter code here`
con = DriverManager.getConnection(host, username, password);
stmt = con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,ResultSet.CONCUR_UPDATABLE);
String SQL = "SELECT * FROM ANDYSHORT.DVDS";
rs = stmt.executeQuery(SQL);
/*
System.out.println("ID Film Name Genre Rating");
System.out.println("-------------------------------");
while (rs.next())
{
int id_col = rs.getInt("ID");
String film_name_col = rs.getString("Film_Name");
String genre_col = rs.getString("Genre");
String rating_col = rs.getString("Rating");
String p = id_col + " " + film_name_col + " " + genre_col + " " + rating_col;
System.out.println(p);
//System.out.format("%32s%10d%16s", id_col , film_name_col, genre_col, rating_col);
}
*/
}
catch (SQLException err)
{
System.out.println(err.getMessage());
}
}
public void GetUserInput()
{
System.out.println();
System.out.println("What would you like to do? Choose one of the following options.");
System.out.println("1. Display DVD library list");
System.out.println("2. Add a new film to database.");
System.out.println("3. Delete a film from the database.");
System.out.println();
Scanner user_option_selection = new Scanner(System.in);
selection = user_option_selection.next();
if(selection.equalsIgnoreCase("1"))
{
DisplayDVDList();
}
else if(selection.equalsIgnoreCase("2"))
{
AddRecord();
}
else if(selection.equalsIgnoreCase("3"))
{
DeleteRecord();
}
else
{
System.out.println("Incorrect option entered. Please try again.");
}
}
public void DisplayDVDList()
{
try
{
String SQL = "SELECT * FROM ANDYSHORT.DVDS";
rs = stmt.executeQuery(SQL);
System.out.println("ID Film Name Genre Rating");
System.out.println("-------------------------------");
while (rs.next())
{
int id_col = rs.getInt("ID");
String film_name_col = rs.getString("Film_Name");
String genre_col = rs.getString("Genre");
String rating_col = rs.getString("Rating");
String p = id_col + " " + film_name_col + " " + genre_col + " " + rating_col;
System.out.println(p);
//System.out.format("%32s%10d%16s", id_col , film_name_col, genre_col, rating_col);
}
}
catch (SQLException err)
{
System.out.println(err.getMessage());
}
GetUserInput();
}
public void AddRecord()
{
Scanner new_film_details = new Scanner(System.in);
System.out.println("Please enter film name: ");
film_name = new_film_details.next();
System.out.println("Please enter film genre: ");
genre = new_film_details.next();
System.out.println("Please enter film rating: ");
rating = new_film_details.next();
try
{
rs.last();
id_num = rs.getRow();
id_num = id_num + 1;
rs.moveToInsertRow();
rs.updateInt("ID", id_num);
rs.updateString("FILM_NAME", film_name);
rs.updateString("GENRE", genre);
rs.updateString("RATING", rating);
rs.insertRow();
//stmt.close( );
//rs.close( );
}
catch(SQLException err)
{
System.out.println(err.getMessage());
}
GetUserInput();
}
public void DeleteRecord()
{
String id = "";
Scanner id_of_film_to_delete= new Scanner(System.in);
System.out.println("Enter ID of film you want to delete.");
id = id_of_film_to_delete.next();
int idInt = Integer.parseInt(id);
try
{
stmt = con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,ResultSet.CONCUR_UPDATABLE);
String sql = "SELECT * FROM ANDYSHORT.DVDS WHERE ID =" + idInt;
rs = stmt.executeQuery(sql);
rs.deleteRow();
}
catch(SQLException err)
{
System.out.println(err.getMessage());
}
GetUserInput();
}
}
use directly this query
"DELETE FROM ANDYSHORT.DVDS WHERE ID =" + idInt;
String sql = "DELETE FROM ANDYSHORT.DVDS WHERE ID=?";
PreparedStatement statement = conn.prepareStatement(sql);
statement.setString(1, "+ idInt+");
int rowsDeleted = statement.executeUpdate();
if (rowsDeleted > 0) {
System.out.println(" delete successfully!");
}
Use prepared statements to avoid SQL injection:
PreparedStatement statement;
statement = con.prepareStatement("DELETE FROM andyshort.dvds WHERE id = ?");
statement.setInt(1, idToDelete);
statement.executeUpdate();
You can directly use delete query if you have the Id before hand.
String sql = "DELETE FROM ANDYSHORT.DVDS WHERE ID =" + idInt;
stmt.executeUpdate(sql);
But, it's better to use prepared statements instead of statements in order to avoid sql injection attacks.
String query= "DELETE FROM ANDYSHORT.DVDS WHERE ID = ? ";
PreparedStatement preparedStatement = con.prepareStatement(query);
preparedStatement.setInt(1,idInt);
preparedStatement.executeUpdate();
You need to move the cursor to the first row before deleting the row, if you want to use deleteRow() method.
rs.first();
rs.deleteRow();
i have a table - emp_details in mysql
i want to seatch an employ's id number in java.
if it is in the table , then show all the details of employee.
otherwise display an error message.
how i do this
Using JDBC
Here is an example You can build your solution from it.
Statement stmt = null;
String query = "select COF_NAME, SUP_ID, PRICE, SALES, TOTAL from " + dbName + ".COFFEES";
try {
stmt = con.createStatement();
ResultSet rs = stmt.executeQuery(query);
while (rs.next()) {
String coffeeName = rs.getString("COF_NAME");
int supplierID = rs.getInt("SUP_ID");
float price = rs.getFloat("PRICE");
int sales = rs.getInt("SALES");
int total = rs.getInt("TOTAL");
System.out.println(coffeeName + "\t" + supplierID + "\t" + price + "\t" + sales + "\t" + total);
}
} catch (SQLException e ) {
JDBCTutorialUtilities.printSQLException(e);
} finally {
stmt.close();
}
ResultSet rs1=stmt.executeQuery("SELECT * FROM employee_details where Employee_ID='"+strEmpId+"'");
if(rs1.next()) {
System.out.println("Emp ID : " + rs1.getString(1));
System.out.println("Emp Name : " + rs1.getString(2));
System.out.println("Emp Salary : " + rs1.getString(3));
} else {
System.out.println("Emp ID not found");
}
If you want to know more about SQL just go through HERE