SQLite DELETE 查询不会从数据库中删除

Question

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.

Answer 1

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.