java - simple validation using loops and result set

Question

This program that checks if there is any repeated username present in the database. The problem is it repeats the insert n times, depending on the number of current usernames in the database.

Here is the code:

ResultSet rs = SQLOperations.getAllUser(connection);            
while (rs.next()) {
  String user=rs.getString("username");
  if (username.equalsIgnoreCase(user)) {
    System.out.println("same username"); 
  } else {
    if(!password.equals(cpassword)) {
      System.out.println("not the same pass and cpass");
    } else {
      if (connection != null) {
        if (SQLOperations.addAccount(account, connection)) {
          System.out.println("successful insert");
        } else {
          System.out.println("failed insert");
        }
      } else {
        System.out.println("invalid connection");
      }

Answer 1

This is because you are repeating the loop for each user in the database and adding the new user each time the user in the database does not have the same username.

You need to create a Boolean that starts as true and changes to false if the user exists in the database. Then, after the loop, you can add the user if the Boolean is true.

For example, you could do:

ResultSet rs = SQLOperations.getAllUser(connection);            
Boolean add = true;
while (rs.next()) {
    String user=rs.getString("username");
    if(username.equalsIgnoreCase(user)){
        System.out.println("same username"); 
        add = false;
        break;
    }
}


if (add) {
    if (connection != null) {
        if (SQLOperations.addAccount(account, connection)){
            System.out.println("successful insert");
        } else {
            System.out.println("failed insert");
        }
    } else {
        System.out.println("invalid connection");
    }
}

Answer 2

Your actual problem is a design problem. Your methods should do exactly one thing and one thing only. In this program, there are three things being done: checking the database for other accounts and inserting an account, while the third thing is checking for connections. Instead:

//This function checks to see if a user exists
public boolean userExists(Connection conn, String username) {
  ResultSet rs = SQLOperations.getAllUser(connection);            
  while (rs.next()) {
    String user=rs.getString("username");
    if (username.equalsIgnoreCase(user)) {
      return true;//This is the only thing we care about
    }
  }
  return false;//We didn't find a duplicate username.
}

//This is our gateway function, but it actually is doing validation
public void insertNewUser(Connection conn, String username, String password, String confirmpassword) {
  if (userExists(conn, username) { //Note this is our validation logic
    System.out.println("Same username! Cannot add this account.");//probably should be an exception or return value, not println
  } else { //we have validated the user, now validate password
    if(!password.equals(cpassword)) {
      System.out.println("not the same pass and cpass");
    } else {
      if (addUser(Connection conn, String username, String password)) {
        System.out.println("Successfully added.");
      } else {
        System.out.println("Attempt to add user to db failed.");
      }
    }
  }
} //note that we do nothing else in this function!

//Note this function assumes you've already run a validation check
private boolean addUser(Connection conn, String username, String password) {
  if (connection != null) {//I think this is probably not the right place for this, but sure.
    if (SQLOperations.addAccount(account, connection)) {
      return true;
    } else {
      return true;
    }
  } else {
    return false;
  }
}

Note each function does exactly one thing (except for the last function, which should really be two functions or have intelligent exceptions to handle the dead connection case). By doing this you keep your code much cleaner. In fact, this code becomes even cleaner if you do use exceptions, and an exception-handling function. I highly recommend Clean Code as a book that will help you think more critically about this stuff.

Answer 3

Of course it does,You should change your logic of checking uniqueness.

There are several points to correct in your code.

1)Just fetch the account row from database by passing username,If row is presented,User exists.

2)And checking for same password is totally not accepted by any user,Because 2 members can have same password,but not the username