CSE 530A. DAOs and MVC. Washington University Fall 2012

Transcription

1 CSE 530A DAOs and MVC Washington University Fall 2012

2 Model Object Example public class User { private Long id; private String username; private String password; public Long getid() { return id; public void setid(long id) { this.id = id; public String getusername() { return username; Model Objects are pure data objects POJOs (Plain Old Java Objects) in Java public void setusername(string username) { this.username = username; public String getpassword() { return password; public void setpassword(string password) { this.password = password;

3 public class UserDao { public User getuserbyid(connection con, Long id) throws SQLException { public User authenticateuser(connection con, String username, String password) throws SQLException { public void deleteuser(long id) { public void updateuser(connection con, User user) throws SQLException { public User createuser(connection con, String username, String password) throws SQLException { Data Access Objects provide a low-level interface to persistent data Provide CRUD methods

4 private static final String GET_USER_BY_ID = "select user_id, username, password from users where id =?"; public User getuserbyid(connection con, Long id) throws SQLException { PreparedStatement stmt = null; ResultSet rs = null; stmt = con.preparestatement(get_user_by_id); stmt.setlong(1, id); rs = stmt.executequery(); if (!rs.next()) { return null; User user = new User(); user.setid(rs.getlong(1)); user.setusername(rs.getstring(2)); user.setpassword(rs.getstring(3)); // Should we check for multiple users with the same id? return user; finally { DatabaseManager.closeResultSet(rs); DatabaseManager.closeStatement(stmt);

5 private static final String AUTHENTICATE_USER = "select user_id, username, password from users where username =? and password =?"; public User authenticateuser(connection con, String username, String password) throws SQLException { PreparedStatement stmt = null; ResultSet rs = null; stmt = con.preparestatement(authenticate_user); stmt.setstring(1, username); stmt.setstring(2, password); rs = stmt.executequery(); if (!rs.next()) { return null; User user = new User(); user.setid(rs.getlong(1)); user.setusername(rs.getstring(2)); user.setpassword(rs.getstring(3)); // Should we check for multiple users with the same username and password? return user; finally { DatabaseManager.closeResultSet(rs); DatabaseManager.closeStatement(stmt);

6 private static final String UPDATE_USER = "update users set username =?, password =? where user_id =?"; public void updateuser(connection con, User user) throws SQLException { PreparedStatement stmt = null; stmt = con.preparestatement(update_user); stmt.setstring(1, user.getusername()); stmt.setstring(2, user.getpassword()); stmt.setlong(3, user.getid()); /* int count = */ stmt.executeupdate(); // Should we throw an exception if the count is not 1? finally { DatabaseManager.closeStatement(stmt);

7 private static final String CREATE_USER = "insert into users (username, password) values (?,?)"; public User createuser(connection con, String username, String password) throws SQLException { PreparedStatement stmt = null; stmt = con.preparestatement(create_user); stmt.setstring(1, username); stmt.setstring(2, password); /* int count = */ stmt.executeupdate(); // Should we throw an exception if the count is not 1? return authenticateuser(con, username, password); finally { DatabaseManager.closeStatement(stmt); Kind of ugly to have to get the user we just created

8 private static final String CREATE_USER = "insert into users (username, password) values (?,?)"; private static final String GET_CREATED_USER_ID = "select currval('users_user_id_seq')"; public User createuser(connection con, String username, String password) throws SQLException { PreparedStatement stmt = null; ResultSet rs = null; stmt = con.preparestatement(create_user); stmt.setstring(1, username); stmt.setstring(2, password); /* int count = */ stmt.executeupdate(); // Should we throw an exception if the count is not 1? stmt = con.preparestatement(get_created_user_id); rs = stmt.executequery(); if (!rs.next()) { // What should we do?

9 User user = new User(); user.setid(rs.getlong(1)); user.setusername(username); user.setpassword(password); return user; finally { DatabaseManager.closeResultSet(rs); DatabaseManager.closeStatement(stmt); currval() is an example of a database function Returns the last value for a sequence in your session PostgreSQL has many built-in functions Later, we will see how to create our own functions

10 MVC The Model-View-Controller pattern separates the presentation (the View), the data model, and the application logic from each other Many variations Primary focus is separation of concerns between the Model, View, and Controller Boundary between view-specific controller and application logic often blurry

11 MVC Example from Spring Web framework

12 MVC Proper separation of view (and supporting controller) from model and application logic can allow for integration with different front ends Web client (browser-based), web service, desktop client, mobile application

13 Controller Example public class Controller { private static final Logger LOGGER = Logger.getLogger(Controller.class.getName()); private DatabaseManager dbm; private UserDao userdao = new UserDao(); public Controller(DatabaseManager dbm) { this.dbm = dbm; public User createuser(string username, String password) { User user = null; Connection con = null; con = dbm.getconnection(); con.setautocommit(false); user = userdao.createuser(con, username, password); con.commit(); catch (Exception e) { LOGGER.log(Level.SEVERE, "error creating user", e); con.rollback(); catch (SQLException re) { LOGGER.log(Level.SEVERE, "error in rollback", re); finally { DatabaseManager.closeConnection(con); return user;