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POCircular reference between Assemblies in C# and Visual Studio 2005
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copied!<p>I am working hard to standardize one single way of Layered/n-Tiered design of my all applications.</p> <p>I am trying to make all my applications 5 tiered.</p> <p>Code:</p> <hr> <h2>| UI |</h2> <h2> |</h2> <h2>| Business Object |</h2> <h2> |</h2> <h2>| OR-Mapper |</h2> <h2> |</h2> <h2>| Data Access |</h2> <h2> |</h2> <h2>| RDBMS |</h2> <p>Suppose I am developing an application with a log-in/log-out capability for users. I am creating 4 projects under a VS2005 solution. Each project is for one of the upper 4 layers. I am designing my Business Object class as follows:-</p> <pre><code>public class User { private string _username; public string Username { get { return _username; } set { _username = value; } } private string _password; public string Password { get { return _password; } set { _password = value; } } public User() { } public bool LogIn(String username, String password) { bool success = false; if (UserMapper.UsernameExists(username)) { success = UserMapper.UsernamePasswordExists(username, password); } else { //do nothing } return success; } public bool LogOut() { bool success; //----some logic return success; } public static User GetUserByUsername(string username) { return UserMapper.GetUserByUsername(username); } public static UserCollection GetByUserTypeCode(string code) { return UserMapper.GetByUserTypeCode(code); } } </code></pre> <p>This is how I am giving my objects some functionality that matches the real-world scenario. Here GetByUsername() and GetByUserTypeCode() are getter functions. These functions does't match a real-world logic. Coz, in real-world, a User never "Gets by Username" or "Gets by UserTypeCode". So these functions are kept static.</p> <p>My class for O-R Mapper layer is as follows:-</p> <pre><code>public static class UserMapper { public static bool UsernameExists(String username) { bool exists = false; if (UserDA.CountUsername(username) == 1) { exists = true; } return exists; } public static bool UsernamePasswordExists(String username, String password) { bool exists = false; if (UserDA.CountUsernameAndPassword(username, password) == 1) { exists = true; } return exists; } } </code></pre> <p>And finally, the DA class is as follows:-</p> <pre><code>public static class UserDA { public static int CountUsername(string username) { int count = -1; SqlConnection conn = DBConn.Connection; if (conn != null) { try { SqlCommand command = new SqlCommand(); command.Connection = conn; command.CommandText = @"SELECT COUNT(*) FROM User WHERE User_name = @User_name"; command.Parameters.AddWithValue("@User_name", username); command.Connection.Open(); object idRaw = command.ExecuteScalar(); command.Connection.Close(); if (idRaw == DBNull.Value) { count = 0; } else { count = (int)idRaw; } } catch (Exception ex) { count = -1; } } return count; } public static int CountUsernameAndPassword(string username, string password) { int count = 0; SqlConnection conn = DBConn.Connection; if (conn != null) { try { SqlCommand command = new SqlCommand(); command.Connection = conn; command.CommandText = @"SELECT COUNT(*) FROM User WHERE User_name = @User_name AND Pass_word = @Pass_word"; command.Parameters.AddWithValue("@User_name", username); command.Parameters.AddWithValue("@Pass_word", password); command.Connection.Open(); object idRaw = command.ExecuteScalar(); command.Connection.Close(); if (idRaw == DBNull.Value) { count = 0; } else { count = (int)idRaw; } } catch (Exception ex) { count = 0; } } return count; } public static int InsertUser(params object[] objects) { int count = -1; SqlConnection conn = DBConn.Connection; if (conn != null) { try { SqlCommand command = new SqlCommand(); command.Connection = conn; command.CommandText = @"INSERT INTO User(ID, User_name, Pass_word, RegDate, UserTypeCode, ActualCodeOrRoll) VALUES(@ID, @User_name, @Pass_word, @RegDate, @UserTypeCode, @ActualCodeOrRoll)"; command.Parameters.AddWithValue("@ID", objects[0]); command.Parameters.AddWithValue("@User_name", objects[1]); command.Parameters.AddWithValue("@Pass_word", objects[2]); command.Parameters.AddWithValue("@RegDate", objects[3]); command.Parameters.AddWithValue("@UserTypeCode", objects[4]); command.Parameters.AddWithValue("@ActualCodeOrRoll", objects[5]); command.Connection.Open(); count = command.ExecuteNonQuery(); command.Connection.Close(); } catch (Exception ex) { count = -1; } } return count; } public static SqlDataReader GetUserByUsername(string username) { SqlDataReader dataReader = null; SqlConnection conn = DBConn.Connection; if (conn != null) { try { SqlCommand command = new SqlCommand(); command.Connection = conn; command.CommandText = @"SELECT * FROM User WHERE User_name = @User_name"; command.Parameters.AddWithValue("@User_name", username); command.Connection.Open(); dataReader = command.ExecuteReader(CommandBehavior.CloseConnection); } catch (Exception ex) { dataReader.Close(); dataReader.Dispose(); } } return dataReader; } public static SqlDataReader GetUserByUserTypeCode(string userTypeCode) { SqlDataReader dataReader = null; SqlConnection conn = DBConn.Connection; if (conn != null) { try { SqlCommand command = new SqlCommand(); command.Connection = conn; command.CommandText = @"SELECT * FROM User WHERE UserTypeCode = @UserTypeCode"; command.Parameters.AddWithValue("@UserTypeCode", userTypeCode); command.Connection.Open(); dataReader = command.ExecuteReader(CommandBehavior.CloseConnection); } catch (Exception ex) { dataReader.Close(); dataReader.Dispose(); } } return dataReader; } } </code></pre> <p>If anyone closely examine the these classes he can understand that, O-R Mapper layer needs the reference of BusinessObject-layer. BusinessObject- layer also needs a reference of O-R Mapper-layer.</p> <p>This should create a circular dependency.</p> <p>How can I avoid this problem?</p> <p>Someone suggested using plain Data Transfer Objects (DTO). But, as far as I know, according to OOP, attributes and functionality of a real-world object should be grouped together as a class. If I use DTO then how can I encapsulate functionality into a class? Moreover I am creating another class without any attribute (BO). To me that is breach of OOP in both ways. If I do so, then what is OOP for in this world? The same answer can be applied for "UserManager" classes.</p> <p>I found a <a href="http://imar.spaanjaars.com/QuickDocId.aspx?quickdoc=476" rel="nofollow noreferrer">blog</a>. </p> <p>It discusses about implementing interfaces. Define a separate interface, implement it in your data class in the BusinessObject and program against your interface in the BusinessObject and in the OR-Mapper layer.</p> <p>But I could not do this.</p> <p>Can anyone show me that with a practical example?</p>

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