How can I insert and delete value in a database in derby in JSP?

Question

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The problem is I cannot delete customer from the database. I can create a new customer, but if I leave blank the fields it create an empty record in

Answer 1

I understand from the previous question where you defined ID as integer, so you should use setInt instead of setString, try as

public void deleteClient(Integer id){

    try {

        createConnection();
        String delete="DELETE FROM CUSTOMER WHERE ID=?";
        PreparedStatement ps=conn.prepareStatement(delete);
        ps.setInt(1, id);
        ps.executeUpdate();
    } catch (Exception e) {
        e.printStackTrace();
    }finally {
        ps.close();
        closeConnection();
    }
}

Id is an integer in the database field where you defined it has a primary key.

Update 1

Use the following in your index.jsp to convert String to int, pass idNum to your method.

 Integer idNum = null;
 String id = request.getParameter("ID");
    if(id != null) {
        try {
            System.out.println("String Id value --> "+id.trim());
            idNum = Integer.parseInt(id.trim());
        }
        catch(NumberFormatException ex) {
            ex.printStackTrace();
        }
    }

Answer 2

Looks like you are not setting the ID in the list

while(rs.next()){
        list.add(rs.getString("ID")); // Add this
        list.add(rs.getString("CNAME"));
        list.add(rs.getString("ADDRESS"));
        list.add(rs.getString("PHONENUMBER"));
    }

Without ID in the list , you wont be able to access the same from the jsp and the same wont be available when you call the delete method.

Another thing is make sure that the ID is string and not int . Usually we keep the key (i.e ID here ) as integer.