4-Tier Architecture in ASP.NET with C#

4-Tier Architecture in ASP.NET with C#	Download source file
Posted on: 10/22/2007 5:17:08 PM by SheoNarayan \| Views: 20657 \| Category: ASP.NET 2.0 \| Level: Intermediate \| Print Article
*Code Updated on 21st April 2008 to support Sorting, Paging and data manipulation through Stored Procedure in DAL* Almost all of us must have heard about 3-Tier architecture but what is this 4-Tier architecture? What are the benefits and how it is different from other architectures?


Well, the architecture I am going to demonstrate here is just enhancement of 3-Tier archicture. In this architecture; you no need of writing long function parameters throughout the layers (as in traditionally 3-Tier archicture has to) and the actual objects of the application will be in a separate tier so that in future you can separately use these objects for enhancements. Change in the object definition can be done without touching the entire Business Access Layers ............ Let me explain you step-wise process of creatioin of 4-Tier architecture application. In this application, I am going to take example of a Person that will have 3 properties: FirstName, LastName, Age. We will create a separate pages to insert these records (default.aspx) into database and list,update,delete records (list.aspx) from database. In this application we will have following 4-Tiers 1. Business Object [BO] 2. Business Access Layer [BAL] 3. Data Access Layer [DAL] 4. UI (4-Tier) folder [UI] Picture - 1 (Solution Explorer) For simplicity reason, I have created separate folders for first 3-tiers into App_Code folder. You can create a separate projects for these tiers and add into forth tier (UI) solution. Lets create above tiers one by one. Business Object [BO - Person.cs] Create a separate folder by right-clicking App_Code folder and name it as BO. Right click this folder and create a new .cs (Class) file named Person.cs. Write following code inside it. - Hide Code int m_PersonID = 0; string m_FirstName = string.Empty; string m_LastName = string.Empty; int m_Age = 0; #region Propertiers public int PersonID { get { return m_PersonID; } set { m_PersonID = value; } } public string FirstName { get { return m_FirstName; } set { m_FirstName = value; } } public string LastName { get { return m_LastName; } set { m_LastName = value; } } public int Age { get { return m_Age; } set { m_Age = value; } } #endregion Properties Here, we are first declaring 4 variables for corresponding properites and defining properties for them.This is your Business Object with all its properties/attributes to work with. Next step is to create Data Access Layer. Data Access Layer [DAL - PersonDAL.cs] The way you created BO folder inside App_Code folder, create another folder named DAL. Create a .cs file inside it and name it as PersonDAL.cs Write following code inside it (You can copy-paste). - Hide Code using System; using System.Data; using System.Configuration; using System.Web; using System.Web.Security; using System.Web.UI; using System.Web.UI.WebControls; using System.Web.UI.WebControls.WebParts; using System.Web.UI.HtmlControls; using System.Data.SqlClient; /// <summary> /// Summary description for PersonDAL /// </summary> public class PersonDAL { string connStr = ConfigurationManager.ConnectionStrings["TutTestConn"].ToString(); public PersonDAL() { } /// <summary> /// Used to insert records into database /// </summary> /// <param name="p"></param> /// <returns></returns> public int Insert(Person person) { SqlConnection conn = new SqlConnection(connStr); conn.Open(); SqlCommand dCmd = new SqlCommand("InsertData", conn); dCmd.CommandType = CommandType.StoredProcedure; try { dCmd.Parameters.AddWithValue("@firstName", person.FirstName); dCmd.Parameters.AddWithValue("@lastName", person.LastName); dCmd.Parameters.AddWithValue("@age", person.Age); return dCmd.ExecuteNonQuery(); } catch { throw; } finally { dCmd.Dispose(); conn.Close(); conn.Dispose(); } } /// <summary> /// Update record into database /// </summary> /// <param name="p"></param> /// <returns></returns> public int Update(Person person) { SqlConnection conn = new SqlConnection(connStr); conn.Open(); SqlCommand dCmd = new SqlCommand("UpdateData", conn); dCmd.CommandType = CommandType.StoredProcedure; try { dCmd.Parameters.AddWithValue("@firstName", person.FirstName); dCmd.Parameters.AddWithValue("@lastName", person.LastName); dCmd.Parameters.AddWithValue("@age", person.Age); dCmd.Parameters.AddWithValue("@personID", person.PersonID); return dCmd.ExecuteNonQuery(); } catch { throw; } finally { dCmd.Dispose(); conn.Close(); conn.Dispose(); } } /// <summary> /// Load all records from database /// </summary> /// <returns></returns> public DataTable Load() { SqlConnection conn = new SqlConnection(connStr); SqlDataAdapter dAd = new SqlDataAdapter("LoadAll", conn); dAd.SelectCommand.CommandType = CommandType.StoredProcedure; DataSet dSet = new DataSet(); try { dAd.Fill(dSet, "PersonTable"); return dSet.Tables["PersonTable"]; } catch { throw; } finally { dSet.Dispose(); dAd.Dispose(); conn.Close(); conn.Dispose(); } } /// <summary> /// Delete record from database /// </summary> /// <param name="person"></param> /// <returns></returns> public int Delete(Person person) { SqlConnection conn = new SqlConnection(connStr); conn.Open(); SqlCommand dCmd = new SqlCommand("DeleteData", conn); dCmd.CommandType = CommandType.StoredProcedure; try { dCmd.Parameters.AddWithValue("@personID", person.PersonID); return dCmd.ExecuteNonQuery(); } catch { throw; } finally { dCmd.Dispose(); conn.Close(); conn.Dispose(); } } } In this class file, we have Insert, Update, Delete, Load methods. In this class file, first I am getting the connection string from the web.config file in a class level variable called connStr and using the same string in all my methods to open the connection. For simplicity reason, I have not shown the code for Stored Procedure, however you can get the complete database and code by downloading the Source Code files. This was your Data Access Layer. Till now you have your Business Object and Data Access Layer ready. Now lets go to the third layer and create Business Access Layer. Business Access Layer [BAL - PersonBAL.cs] Again, right click App_Code folder and add a new folder named BAL. Create a new class file inside it and name it as PersonBAL.cs. Write following code inside it. - Hide Code using System; using System.Data; using System.Configuration; using System.Web; using System.Web.Security; using System.Web.UI; using System.Web.UI.WebControls; using System.Web.UI.WebControls.WebParts; using System.Web.UI.HtmlControls; /// <summary> /// Summary description for PersonBAL /// </summary> public class PersonBAL { public PersonBAL() { } /// <summary> /// insert records into database /// </summary> /// <param name="person"></param> /// <returns></returns> public int Insert(Person person) { PersonDAL pDAL = new PersonDAL(); try { return pDAL.Insert(person); } catch { throw; } finally { pDAL = null; } } /// <summary> /// Update records into database /// </summary> /// <param name="person"></param> /// <returns></returns> public int Update(Person person) { PersonDAL pDAL = new PersonDAL(); try { return pDAL.Update(person); } catch { throw; } finally { pDAL = null; } } /// <summary> /// Load records from database /// </summary> /// <returns></returns> public DataTable Load() { PersonDAL pDAL = new PersonDAL(); try { return pDAL.Load(); } catch { throw; } finally { pDAL = null; } } /// <summary> /// Delete record from database /// </summary> /// <param name="person"></param> /// <returns></returns> public int Delete(Person person) { PersonDAL pDAL = new PersonDAL(); try { return pDAL.Delete(person); } catch { throw; } finally { pDAL = null; } } } Here, we are creating separate methods each for respective PersonDAL.cs methods here. As in our case we don't have any business logic, so we are just instantiating the Data Access Layer objects, using its methods and and returning to UI (fourth layer, described later on). You must have noticed here that in the try catch block, I am just writing throw; statement. This is because when any error will occur it will be send to the calling layers (in our case UI) and there we will handle it. Till now, we have BO, BAL and DAL ready. Now we are left with our application face, I mean UI. Lets first create default.aspx file that will contain one form and textboxs that will be used to enter records. User Interface - [UI]-Default.aspx Create a separate folder in your UI solution named 4-Tier and add one .aspx page called Default.aspx (Picture - 2). In this page, we will write ASP.NET code to render textboxes and buttons. OnClick event of the button we will calll AddRecords method that will ultimately insert the records into database. Below is the code to render the asp.net form. - Hide Code <form id="form1" runat="server"> <div> <p><a href="List.aspx">List Records</a></p> <asp:Label ID="lblMessage" runat="Server" ForeColor="red" EnableViewState="False"></asp:Label> <table style="border:2px solid #cccccc;"> <tr style="background-color:#ECF3AB;"> <th colspan="3">Add Records</th> </tr> <tr> <td> First Name: </td> <td> <asp:TextBox ID="txtFirstName" runat="Server"></asp:TextBox> </td> <td> <asp:RequiredFieldValidator ID="req1" runat="Server" Text="" ControlToValidate="txtFirstName" Display="dynamic"></asp:RequiredFieldValidator> </td> </tr> <tr> <td> Last Name: </td> <td> <asp:TextBox ID="txtLastName" runat="Server"></asp:TextBox> </td> <td> <asp:RequiredFieldValidator ID="req2" runat="Server" Text="" ControlToValidate="txtLastName" Display="dynamic"></asp:RequiredFieldValidator> </td> </tr> <tr> <td> Age: </td> <td> <asp:TextBox ID="txtAge" runat="Server" Columns="4"></asp:TextBox> </td> <td> <asp:RequiredFieldValidator ID="req3" runat="Server" Text="" ControlToValidate="txtAge" Display="dynamic"></asp:RequiredFieldValidator> <asp:CompareValidator ID="Comp1" runat="Server" Text="Only integer" ControlToValidate="txtAge" Operator="DataTypeCheck" Type="Integer"></asp:CompareValidator> </td> </tr> <tr> <td> </td> <td> <asp:Button ID="btnSubmit" runat="server" Text="Submit" OnClick="AddRecords" /> </td> </tr> </table> </div> </form> Picture - 2 (Default.aspx)* AddRecords method - Hide Code protected void AddRecords(object sender, EventArgs e) { //Lets validate the page first if (!Page.IsValid) return; int intResult = 0; // Page is valid, lets go ahead and insert records // Instantiate BAL object PersonBAL pBAL = new PersonBAL(); // Instantiate the object we have to deal with Person person = new Person(); // set the properties of the object person.FirstName = txtFirstName.Text; person.LastName = txtLastName.Text; person.Age = Int32.Parse(txtAge.Text); try { intResult = pBAL.Insert(person); if (intResult > 0) lblMessage.Text = "New record inserted successfully."; else lblMessage.Text = "FirstName [<b>"+ txtFirstName.Text +"</b>] alredy exists, try another name"; } catch (Exception ee) { lblMessage.Text = ee.Message.ToString(); } finally { person = null; pBAL = null; } } In the above method, I am doing following things mainly: 1. Instantiating BAL object 2. Instantiating BO object 3. Settinng properties of BO object by the textbox values 4. Calling Insert method of the BAL object and passing BO object as parameter [pBAL.Insert(person)] in try block 5. Checking for number of records affected, If the number is more than zero, I am writing Success message otherwise Duplicate records found. 6. If any layer will throw any error, I am catching it and displaying to the user in throw block. 7. Whatever objects I had instantiated, I am specifying their values to null to let the GC know that I am no more going to use them. User Interface - [UI]-List.aspx In this page, I am going to use a GridView to List, Modify, Sort and Delete records from the database. Create an .aspx page in the same 4-Tier folder named List.aspx (Picture - 3). Following is the code for the GridView that will do data manipulation for us. - Hide Code <form id="form1" runat="server"> <div> <p><a href="Default.aspx">Add Record</a></p> <asp:Label ID="lblMessage" runat="Server" ForeColor="red" EnableViewState="False"></asp:Label> <asp:GridView ID="GridView1" runat="server" CellPadding="4" ForeColor="#333333" GridLines="None" DataKeyNames="PersonID" AutoGenerateEditButton="True" AutoGenerateColumns="False" OnRowEditing="EditRecord" OnRowUpdating="UpdateRecord" OnRowCancelingEdit="CancelRecord" OnRowDeleting="DeleteRecord" AllowPaging="True" AllowSorting="true" PageSize="5" OnPageIndexChanging="ChangePage" OnSorting="SortRecords"> <FooterStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" /> <RowStyle BackColor="#EFF3FB" /> <EditRowStyle BackColor="#2ff1BF" /> <SelectedRowStyle BackColor="#D1DDF1" Font-Bold="True" ForeColor="#333333" /> <PagerStyle BackColor="#2461BF" ForeColor="White" HorizontalAlign="Center" /> <HeaderStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" /> <AlternatingRowStyle BackColor="White" /> <Columns> <asp:BoundField DataField="PersonID" HeaderText="Person ID" ReadOnly="True" SortExpression="PersonID" /> <asp:TemplateField HeaderText="First Name" SortExpression="FirstName"> <ItemTemplate> <%# Eval("FirstName") %> </ItemTemplate> <EditItemTemplate> <asp:TextBox ID="txtFName" runat="Server" Text='<%# Eval("FirstName") %>'></asp:TextBox> </EditItemTemplate> </asp:TemplateField> <asp:TemplateField HeaderText="Last Name" SortExpression="LastName"> <ItemTemplate> <%# Eval("LastName") %> </ItemTemplate> <EditItemTemplate> <asp:TextBox ID="txtLName" runat="Server" Text='<%# Eval("LastName") %>'></asp:TextBox> </EditItemTemplate> </asp:TemplateField> <asp:TemplateField HeaderText="Age" SortExpression="Age"> <ItemTemplate> <%# Eval("Age") %> </ItemTemplate> <EditItemTemplate> <asp:TextBox ID="txtAge" runat="Server" Text='<%# Eval("Age") %>'></asp:TextBox> </EditItemTemplate> </asp:TemplateField> <asp:TemplateField HeaderText="Delete?"> <ItemTemplate> <span onclick="return confirm('Are you sure to Delete?')"> <asp:LinkButton ID="lnBD" runat="server" Text="Delete" CommandName="Delete"></asp:LinkButton> </span> </ItemTemplate> </asp:TemplateField> </Columns> </asp:GridView> </div> </form> Picture - 3 (List.aspx) On the OnRowEditing, OnRowUpdating, OnRowCancelEdit, OnSorting and OnRowDeleting events we are calling respective methods to do data manipulation. Following are codes to bind the GridView and methods that will fire on GridView events. - Hide Code protected void Page_Load(object sender, EventArgs e) { if (!IsPostBack) BindGrid(); } /// <summary> /// Fired when Cancel button is clicked /// </summary> /// <param name="sender"></param> /// <param name="e"></param> protected void CancelRecord(object sender, GridViewCancelEditEventArgs e) { GridView1.EditIndex = -1; BindGrid(); } /// <summary> /// Fires when Edit button is clicked /// </summary> /// <param name="sender"></param> /// <param name="e"></param> protected void EditRecord(object sender, GridViewEditEventArgs e) { GridView1.EditIndex = e.NewEditIndex; BindGrid(); } /// <summary> /// Fires when Update button is clicked /// </summary> /// <param name="sender"></param> /// <param name="e"></param> protected void UpdateRecord(object sender, GridViewUpdateEventArgs e) { int personID = Int32.Parse(GridView1.DataKeys[e.RowIndex].Value.ToString()); int intResult = 0; GridViewRow row = GridView1.Rows[e.RowIndex]; TextBox tFN = (TextBox) row.FindControl("txtFName"); TextBox tLN = (TextBox)row.FindControl("txtLName"); TextBox tAge = (TextBox)row.FindControl("txtAge"); // instantiate BAL PersonBAL pBAL = new PersonBAL(); Person person = new Person(); try { person.PersonID = personID; person.FirstName = tFN.Text; person.LastName = tLN.Text; person.Age = Int32.Parse(tAge.Text); intResult = pBAL.Update(person); if (intResult > 0) lblMessage.Text = "Record Updated Successfully."; else lblMessage.Text = "Record couldn't updated"; } catch (Exception ee) { lblMessage.Text = ee.Message.ToString(); } finally { person = null; pBAL = null; } GridView1.EditIndex = -1; // Refresh the list BindGrid(); } /// <summary> /// fires when Delete button is clicked /// </summary> /// <param name="sender"></param> /// <param name="e"></param> protected void DeleteRecord(object sender, GridViewDeleteEventArgs e) { int personID = Int32.Parse(GridView1.DataKeys[e.RowIndex].Value.ToString()); // instantiate BAL PersonBAL pBAL = new PersonBAL(); Person person = new Person(); try { person.PersonID = personID; pBAL.Delete(person); lblMessage.Text = "Record Deleted Successfully."; } catch (Exception ee) { lblMessage.Text = ee.Message.ToString(); } finally { person = null; pBAL = null; } GridView1.EditIndex = -1; // Refresh the list BindGrid(); } /// <summary> /// Fires when page links are clicked /// </summary> /// <param name="sender"></param> /// <param name="e"></param> protected void ChangePage(object sender, GridViewPageEventArgs e) { GridView1.PageIndex = e.NewPageIndex; // Refresh the list BindGrid(); } /// <summary> /// Fires when Columns heading are clicked /// </summary> /// <param name="sender"></param> /// <param name="e"></param> protected void SortRecords(object sender, GridViewSortEventArgs e) { DataTable dataTable = GridDataSource(); if (dataTable != null) { DataView dataView = new DataView(dataTable); dataView.Sort = GetSortExpression(e); GridView1.DataSource = dataView; GridView1.DataBind(); } } #region Private Methods /// <summary> /// Bind the gridview /// </summary> private void BindGrid() { GridView1.DataSource = GridDataSource(); GridView1.DataBind(); } /// <summary> /// Get GridView DataSource /// </summary> private DataTable GridDataSource() { PersonBAL p = new PersonBAL(); DataTable dTable = new DataTable(); try { dTable = p.Load(); } catch (Exception ee) { lblMessage.Text = ee.Message.ToString(); } finally { p = null; } return dTable; } /// <summary> /// Get sort expression for the gridview /// </summary> /// <param name="e"></param> /// <returns></returns> private string GetSortExpression(GridViewSortEventArgs e) { string sortDirection = string.Empty; // if clicked on the same column twice then let it toggle the sort order, else reset to ascending if (ViewState["SortExpression"] != null) { if (!ViewState["SortExpression"].ToString().Equals(e.SortExpression.ToLower())) { ViewState["SortDirection"] = null; } } if (ViewState["SortDirection"] != null) { if (ViewState["SortDirection"].ToString().Equals("ASC")) { sortDirection = "DESC"; ViewState["SortDirection"] = "DESC"; } else { sortDirection = "ASC"; ViewState["SortDirection"] = "ASC"; } } else { ViewState["SortDirection"] = "ASC"; } ViewState["SortExpression"] = e.SortExpression.ToLower(); return e.SortExpression + " " + sortDirection; } #endregion Private Methods Thats it!!! Now we have done all our home work, Its time to enjoy now. Just build the application by pressing Ctrl+Shift+B, once it shows Build Succeeded in the status bar at the bottom, you are ready to enjoy your 4-Tier architecture application. Browse it as http://localhost/4-Tier (Provided you have created "4-Tier" virtual directory in your IIS or you can choose your own virtual directory name), you should see your screens as shown above (default.aspx and list.aspx pages). Try manipulating data and see how effectively its happening. This was a simple application, based on this architecture, you can create larger application by adding separate objects and their corresponding tiers. In order to use namespace in different tiers, you should define your namespace in respective tiers objects and use those namespace by using statement whereever you need. I have also attached a ready to use sample code of this example, Download it and use it!!! Thanks & Happy Coding.

Response(s) to this Article

Posted by: Tbroyer | Posted on: 24 Oct 2007 12:18:46 AM

Your BO "tier" is what I call a set of DTOs (Data Transfer Objects), it's neither new nor a "tier": DTOs are used to pass data from one tier to the other: they have no embedded "business logic", they're just data "containers".

Author's response: Please see the 2nd paragraph of this article. It explains the purpose and its benefits. Thanks.

Posted by: Wesc | Posted on: 24 Oct 2007 06:11:00 AM

This is normal, everyday 3-tier: Presentation, BLL, and DAL. The object you're passing back and forth is not a tier any more than a String or Integer would be. But, it's a fine article for someone who wants a simple explanation of DTOs.

Author's response: Please see the 2nd paragraph of this article. It explains the purpose and its benefits. Thanks.

Posted by: Damieng | Posted on: 26 Oct 2007 12:52:33 AM

This sample suffers from both SQL injection and HTML injection making it a very insecure. Get rid of building those SQL strings and use parameterised queries and ensure that output added to the HTML is correctly HttpUtility.Encoded.

Author's response: Thanks for your feedback Damieng. Sql statement has been used here to make the tutorial simple, it is informed in the DAL description. Regards

Posted by: Amitgupta007_99 | Posted on: 26 Oct 2007 05:19:16 AM

Basically, it's all about components. If the UI (presentation) logic is mixed up with the business (task) logic, this is going to be a bear to do. You'll have to slog through all that code and filter out the business code from the presentation code. But if you put these into separate components (n tiers), you can easily plug your business code into any type of user interface or API.

Think of each tier as a black box that only has functionality that is related to what it needs to do. The tiers can just be logical or physical. In the example above it's move a physical tiers.When it comes to performance this would be very very fast and scalable too.

There's more to it, of course, but that's the basic principle Software evolves. Build it for evolution, extensibility, scalability.......and I am very sure this 4 tier architecture will helps us a great deal in improving the future of application.

Amit P Gupta
Web Strategist
amit@r2ainformatics.com

Posted by: Vijay.a.nikam | Posted on: 02 Dec 2007 01:06:57 AM

Good one

Posted by: Vijay.a.nikam | Posted on: 28 Jan 2008 07:51:37 AM

Hello,
This is very good article. I have some questions.
1. Where to maintain transaction.
2. If I am using inheritance. Then their is need to create a diffent DAL classes base class and each derived cass.

Posted by: Ravimama | Posted on: 11 Apr 2008 06:06:15 AM

Consider your BO, you have member variables. Why not expose them as public variables?

What is the exact purpose of using the properties?

Sorry if my question is too dumb. But I want to get things clear.

Posted by: SheoNarayan | Posted on: 11 Apr 2008 10:01:30 AM

Hi Vijay.a.nikam,

For your point 1 - You can use transaction in Data Access Layer.
Point 2 - I couldn't get you.

Posted by: SheoNarayan | Posted on: 11 Apr 2008 10:04:41 AM

HI Ravimama,

To answer your question, I will suggest to visit following link

http://www.developersdex.com/csharp/message.asp?p=1111&r=6148128
http://www.eggheadcafe.com/software/aspnet/31582165/getset-vs-public-variabl.aspx
http://channel9.msdn.com/ShowPost.aspx?PostID=299396

Thanks

Posted by: Akeenlearner | Posted on: 31 May 2008 11:07:54 PM

Hi, this is good, thanks. But i have a concern. I am speaking from a Windows App point of view but have yet to try this on a web app.

Supposedly, you have created separate project for each of the Layers. Let's just say the BO and BAL are in the same project. To use your objects you would have to add reference to it. However this would result in a circular dependency which is not allowed. If you had reference the dll file instead, this would also result in a error that you have made more than a file reference to a assembly when you reference the assembly in your presentation layer.

I am referring to your statement when you mentioned "You can create a separate projects for these tiers and add into forth tier (UI) solution."

Thanks, I'm still learning

Posted by: SheoNarayan | Posted on: 01 Jun 2008 10:51:30 PM

Hi Akeenlearner,

Thanks for your response. If you are creating separate project for all these layers, you will need following:

1. You will need to create separate projects for all layers BO, BAL, DAL, UI.
2. You will need to add reference of BO into all UI, BAL and DAL. If you will have BO and BAL into same project then you will get circular reference error.
3. Your BO is nothing but a your object Entities layer that will work as a passing objects from one layer to another layer (Mostly similar to DTO but represent all entities of your application)

Please let me know if you have still some question.

4-Tier Architecture in ASP.NET with C#

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