Here's my code for the addStudent:
#FXML
private void addStudent(ActionEvent event) {
// sql query to insert data into students at ID, first name, last name, email and DOB
String sqlInsert = "INSERT INTO students(id,fname,lname,email,DOB) VALUES (?,?,?,?,?)";
try {
Connection conn = dbConnection.getConnection();
PreparedStatement stmt = conn.prepareStatement(sqlInsert);
// add the data in the right column
stmt.setString(1, this.id.getText());
stmt.setString(2, this.firstname.getText());
stmt.setString(3, this.lastname.getText());
stmt.setString(4, this.email.getText());
stmt.setString(5, this.dob.getEditor().getText());
stmt.execute();
conn.close();
} catch(SQLException ex) {
ex.printStackTrace();
}
}
And here's my code for removeStudent:
#FXML
private void removeStudent(ActionEvent event) {
try {
// sql query to delete data from the database
String sqlRemove = "DELETE FROM students WHERE id = ?";
// open a connection to the database and use PreparedStatement to
// initialize the query.
Connection conn = dbConnection.getConnection();
PreparedStatement delete = conn.prepareStatement(sqlRemove);
// information needed to delete the row
delete.setString(1, selectStudent());
// execute and delete
delete.executeUpdate();
// close the connection
conn.close();
} catch (SQLException ex) {
ex.printStackTrace();
}
// update table after deleting
loadStudentData(event);
}
The picture above is the view of my table. I hit LoadData and my table values show up. I want to be able to click on a row(student) and hit Delete Student to remove it.
Helper method for removeStudent:
private String selectStudent() {
String result = "";
try {
String sqlSelect = "SELECT id FROM students";
Connection conn = dbConnection.getConnection();
ResultSet rs = conn.createStatement().executeQuery(sqlSelect);
result = rs.getString(1);
conn.close();
} catch (SQLException ex) {
ex.printStackTrace();
}
return result;
}
I'm pretty sure it has to do with when I "click" on a row, the id value for that isn't being held anywhere so when I hit "Delete" nothing is being given for it to Delete.
I don't know. Any advice would be awesome. :D
First edit: nothing is assigned to delete.setString(1, this.id.getText()). When I click on the row and hit delete, nothing is happening because there's nothing being assigned to id when I click on the row. The query string DOES work however when I physically give it an ID to delete. Also verified that the button does work; it prints out a lovely message for me with a good ol' System.out.println("expletive");
Second edit: Ok, so I updated the removeStudent code and now all I get is the string "null" returned. Nothing deletes. Nothing updates. Nothing is happening except I get "null" in the console.
Third edit: Getting closer! With the realization that the removeStudent isn't being given an ID to delete, I decided to create a private helper method that will do a SELECT query. Now, when I hit delete, it'll delete....but from the top, and not at where I want it selected. The code is above.
Fourth edit: Getting even closer! So, I figured out how to capture the row I click on within the table and I can delete......however, because of my sqlRemove command, I'm deleting by id so if I click on a row with index 3, then ONLY the row within the table that has an id of 3 will be deleted, nothing else. I gotta re-write how the sqlRemove command is worded.
I fixed it:
private String selectStudent() {
// initial value for result to return
String result = "";
// grab the index of the row selected on the table
int initial = studenttable.getSelectionModel().getSelectedIndex();
try {
// SELECT query to execute
String sqlSelect = "SELECT id FROM students";
Connection conn = dbConnection.getConnection();
ResultSet rs = conn.createStatement().executeQuery(sqlSelect);
// while there's a next row
while(rs.next()) {
// set temp to equal the id rs.next() is currently on
String temp = rs.getString("id");
// get the row id - 1 since we start at 0
int temp1 = rs.getRow() - 1;
// if temp1 is equal to the index we selected
if(temp1 == initial) {
// make it equal to result
result = temp;
}
}
// close the connection
conn.close();
} catch (SQLException ex) {
ex.printStackTrace();
}
// return the row to delete
return result;
}
What's going on is in the comments. I finally figured out how to pass the value from a selected row and compare it to a row. Once I get the correct row to pass, I give it to the delete function to remove.
After a day in a half.............but I love it, so. Yeah.
Related
I'm trying to my a very simple webapplication, webshop, for cupcakes.
From the webApp you can choose a cupcake form the dropdown with three attributes
(top, bottom, quantity). These are stored in an ArrayList on my sessionScope but all in numbers e.g. Chokolate as 1 and Vanilla as 2. I want to use these topId numbers to ask my DB (MySQL) for what is in 1 and then have it return Chokolate.
I think I am almost there with my code, but can't get it to return my String, as my topId is an Int.
public static Top getTopById(int topId) {
readFromArrayPutInSQL();
String sql = "INSERT INTO cupcaketopping (toppingType, toppingPrice) VALUES (?, ?)";
try {
ConnectionPool connectionPool = new ConnectionPool();
String query = "SELECT toppingType FROM cupcaketopping";
Statement statement = connectionPool.getConnection().createStatement();
ResultSet rs = statement.executeQuery(query);
rs.getString(topId);
} catch (SQLException e) {
throw new RuntimeException(e);
}
return topId; //Here is the problem - I GUESS?
}
Code after changes due to input in comments, seem to be working!
public static Top getTopById(int topId) {
readFromArrayPutInSQL();
String query = "SELECT toppingType FROM cupcaketopping WHERE toppingID = "+topId+"";
try {
ConnectionPool connectionPool = new ConnectionPool();
PreparedStatement preparedStatement = connectionPool.getConnection().prepareStatement(query);
ResultSet rs = preparedStatement.executeQuery(query);
rs.next();
return new Top(rs.getString(1));
//connectionPool.close(); //NOTE! Won't run, IntelliJ is asking me to delete!
} catch (SQLException e) {
throw new RuntimeException(e);
}
}
There are a few problems:
You're selecting all rows from the cupcaketopping table, regardless of the topId. You should probably be using a PreparedStatement, and then use topId as part of your query.
You never call ResultSet#next(). The result set always starts "before" the first row. You have to call next() for each row in the result set (it returns true if there is a row to read).
The ResultSet#getString(int) method gets the String value of the column at the given index of the result. You only select one column, so the argument should probably be 1 (not topId).
You never close the Statement when done with it.
Depending on how your connection pool class works, you might actually need to close the Connection instead.
You never try to use the String returned by rs.getString(topId).
You never try to convert the query result to a Top instance.
Given it's possible the query will return no result, you might want to consider making the return type Optional<Top>.
The sql string seems to have no purpose.
Your code should look more like this:
public Optional<Top> getTopById(int topId) {
Connection conn = ...;
String query = "SELECT toppingType FROM cupcaketopping WHERE id = ?";
// closes the statement via try-with-resources
try (PreparedStatement stat = conn.prepareStatement(query)) {
stat.setInt(1, topId);
ResultSet rs = stat.executeQuery();
// assume unique result (as it's assumed the ID is the primary key)
if (rs.next()) {
// assumes 'Top' has a constructor that takes a 'String'
return Optional.of(new Top(rs.getString(1)));
} else {
return Optional.empty();
}
} catch (SQLException ex) {
throw new RuntimeException(ex);
}
}
Your actual implementation may vary, depending on how the rest of your code is designed.
I have a JTable bound to MySQL. I already have done code to insert data.
But i don't know how to delete.
I have this sample delete method that works in other simple projects.
public String deleteItem(String name) {
String answer = "";
try {
Connection con = Connect.getConnection();
String sql = "Delete FROM item where name = ?";
PreparedStatement ps = con.prepareStatement(sql);
ps.setString(1, name);
ps.executeUpdate();
ps.close();
con.close();
answer = "OK";
} catch (Exception e) {
answer = e.toString();
}
return answer;
}
Even when I worked with an unbound table I have done this remove row from jtable that did well for me.
But now its a table bound to MySQL and I can't find a way to delete row... already searched on the internet. Found nothing.
PS: i'm using netbeans. i right-clicked jtable > bind > elements , to bind table.
Oh, I found a way!
First, I changed my deleteItem method, to delete by id
ItemDAO.java
public String deleteItem(int ID_item) {
String answer = "";
try {
Connection con = Connect.getConnection();
String sql = "Delete FROM item where ID_Item = ?";
PreparedStatement ps = con.prepareStatement(sql);
ps.setInt(1, ID_item);
ps.executeUpdate();
ps.close();
con.close();
answer = "OK";
} catch (Exception e) {
answer = e.toString();
}
return answer;
}
Then the action in delete button goes like this.
Form.java
private void btnDeleteActionPerformed(java.awt.event.ActionEvent evt) {
int column = 0; // get the first column which is ID_Item
int row = tableItem.getSelectedRow(); //get row selected by user
int value = (int) tableItem.getModel().getValueAt(row, column); // store ID_Item value
String answer = new ItemDAO().deleteItem(value); // call up deleteItem method
if(answer.equals("OK")) {
System.out.println("OK"); // just for test
itemList.clear(); // this is needed to update the bound table after Insert/Delete/Update etc
itemList.addAll(itemQuery.getResultList()); // same as above comment
}else{
System.out.println("ERROR"); // just for test.
}
Maybe isn't the most beautiful way to do it, but it works.
Hey guys I'm trying to scroll through the rows in my database. For some reason my previous and next buttons are not working. Next button displays just first row and previous button doesn't display anything. My first and last buttons are working.
private void previousbtnActionPerformed(java.awt.event.ActionEvent evt) {
try
{
con = DriverManager.getConnection(CONN_STRING, USERNAME, PASSWORD);
Statement st = con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY);
ResultSet rs = st.executeQuery("SELECT * FROM EMPLOYEE");
if (rs.previous())
{
str1 = rs.getString("emp_id");
emp_id.setText(str1);
str2 = rs.getString("emp_fname");
first_name.setText(str2);
str3 = rs.getString("emp_lname");
last_name.setText(str3);
}
else
{
rs.next();
}
con.close();
}
catch (SQLException err)
{
JOptionPane.showMessageDialog(EmployeeGUI.this, err.getMessage());
}
}
private void nextbtnActionPerformed(java.awt.event.ActionEvent evt) {
try
{
con = DriverManager.getConnection(CONN_STRING, USERNAME, PASSWORD);
Statement st = con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_UPDATABLE);
ResultSet rs = st.executeQuery("select * from employee");
if (rs.next())
{
str1 = rs.getString("emp_id");
emp_id.setText(str1);
str2 = rs.getString("emp_fname");
first_name.setText(str2);
str3 = rs.getString("emp_lname");
last_name.setText(str3);
}
else
{
rs.previous();
}
}
catch (SQLException err)
{
JOptionPane.showMessageDialog(EmployeeGUI.this, err.getMessage());
}
}
Here's the javadoc for ResultSet and this is what it says:
A ResultSet object maintains a cursor pointing to its current row of
data. Initially the cursor is positioned before the first row. The
next method moves the cursor to the next row, and because it returns
false when there are no more rows in the ResultSet object, it can be
used in a while loop to iterate through the result set.
So, when you get the ResultSet object, it will always be placed before the previous row and hence, previous() will always return false.
Assuming you are trying to implement Pagination with these buttons, I would recommend having a look at MySQL SELECT documentation and use limit to get the rows, e.g.:
SELECT * FROM tbl LIMIT 5,10; # Retrieve rows 6-15
You can use it with LIMIT i, 1 where i will increment with each click of next and decrement with each click of previous.
I have a table with this columns (id,name,isbn,borrowedStatus(varchar),Date) and some rows in my table.
Now i want to get borrowedStatus value for a specific id,then i need to recognize that String (yes, or no).
Here is my code:
public void booksTableBorrowChanged(int rowInModel) {
Object bookId = this.getValueAt(rowInModel, 0);
Connection con;
PreparedStatement ps1;
String query1 = "select borrowedStatus from books where id=" + bookId;
ResultSet rs = null;
try {
con = DriverManager.getConnection(...);
ps1 = con.prepareStatement(query1);
rs = ps1.executeQuery();
if (String.valueOf(rs.getString("BorrowedStatus")).equalsIgnoreCase("No")) { // then do Borrow Action
System.out.println("Old statuse : No");
// then do other stuff
}
} catch (SQLException sqle) {
sqle.printStackTrace();
}
}
But this code has this exception when executed:
java.sql.SQLException: Before start of result set
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1073)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:987)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:982)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:927)
...
How can i solve this problem?
From ResultSet's Javadoc:
ResultSet object maintains a cursor pointing to its current row of data. Initially the cursor is positioned before the first row. The next method moves the cursor to the next row, and because it returns false when there are no more rows in the ResultSet object, it can be used in a while loop to iterate through the result set.
Notice the sentence starting with "Initially": You first have to call next before being able to access any data.
I am currently working on a Java project (on NetBeans) and I am struggling with a problem.
In fact, I have a jTable which contains several elements, which element has a jCheckBox in the second column and I would like to make a query to add the selected element (selected by the jCheckBox of course) in a table.
I can get the data that I want to add, but my query works only once. I have already check my loop but I don't where the problem comes from.
I let you see the code :
try {
// Getting id of the selected value in the jComboBox
String idParcours = oParcoursDAO.findIdParcours(jComboBoxParcours.getSelectedItem().toString());
int id = Integer.parseInt(idParcours);
// for each value in the jTable
for(int i=0; i <jTable2.getRowCount(); i++){
boolean isChecked = (Boolean)jTable2.getValueAt(i, 1);
String nomPoi = (String)jTable2.getValueAt(i, 0);
// if the value is selected
if(isChecked){
String IDPoi = oParcoursDAO.findIdPoi(nomPoi);
int idpoi = Integer.parseInt(IDPoi);
System.out.println("idpoi "+idpoi); // It works I saw as idpoi as I have choose
System.out.println("id "+id) // It works too
oParcoursDAO.addPoi(idpoi,id); // it works only once
}
}
}catch (SQLException ex) {
Logger.getLogger(ModificationParcoursJInternalFrame.class.getName()).log(Level.SEVERE, null, ex);
}
Thank you in advance for your help.
This is my statement
public void addPoi(int idPoi,int idParcours) throws SQLException{
String query = "INSERT INTO TB_POI_PARCOURS (id_poi,id_parcours) VALUES (?,?) ";
PreparedStatement preparedStatement = conn.prepareStatement(query);
preparedStatement.setInt(1,idPoi);
preparedStatement.setInt(2,idParcours);
preparedStatement.executeUpdate();
preparedStatement.close();
}
Why are you running one query per line? You can execute all of them in a single SQL using batch queries. It will require you to change the code but it will make it more efficient:
public void addPoi(Map<integer,Integer> poiMap) throws SQLException{
String query = "INSERT INTO TB_POI_PARCOURS (id_poi,id_parcours) VALUES (?,?) ";
PreparedStatement preparedStatement = conn.prepareStatement(query);
for(Integer idPoi:poiMap.keySet()) {
preparedStatement.setInt(1,idPoi);
preparedStatement.setInt(2,poiMap.get(idPoi));
preparedStatement.addBatch();
}
preparedStatement.executeBatch();
preparedStatement.close();
}
Of course the original method has to be changed accordingly.