What is a 3-tier architecture?
Three-tier (layer) is a client-server architecture in which the user interface, business process (business rules) and data storage and data access are developed and maintained as independent modules or most often on separate platforms. Basically, there are 3 layers, tier 1 (presentation tier, GUI tier), tier 2 (business objects, business logic tier) and tier 3 (data access tier). These tiers can be developed and tested separately.
What is the need for dividing the code in 3-tiers? Separation of the user interface from business logic and database access has many advantages.
Some of the advantages are as follows:
1.Reusability of the business logic component results in quick development. Let's say we have a module that handles adding, updating, deleting and finding customers in the system. As this component is developed and tested, we can use it in any other project that might involve maintaining customers.
2.Transformation of the system is easy. Since the business logic is separate from the data access layer, changing the data access layer won�t affect the business logic module much. Let's say if we are moving from SQL Server data storage to Oracle there shouldn�t be any changes required in the business layer component and in the GUI component.
3.Change management of the system is easy. Let's say if there is a minor change in the business logic, we don�t have to install the entire system in individual user�s PCs. E.g. if GST (TAX) is changed from 10% to 15% we only need to update the business logic component without affecting the users and without any downtime.
4.Having separate functionality servers allows for parallel development of individual tiers by application specialists.
5.Provides more flexible resource allocation. Can reduce the network traffic by having the functionality servers strip data to the precise structure needed before sending it to the clients.
Using the code
This component has 3 tiers.
Tier 1 or GUI tier with a form will be called FrmGUI,
tier 2 or business logic will be called BOCustomer short for Bussniess Object Customer and finally the
tier 3 or the data tier will be called DACustomer short for Data Access Customer. I have compiled all the 3 tiers in the same project for ease of work. I am including all the source code along with the MS Access database that is used to test this project in the included zip file.
User Interface tierThis is a chunk of code from the user interface. I am only including the functions that are used to call the middle tier or the business logic layer.
I am keeping a reference to business logic layer as BOCustomer.
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Copy Code//This function get the details from the user via GUI
//tier and calls the Add method of business logic layer.
private void cmdAdd_Click(object sender, System.EventArgs e)
{
try
{
cus = new BOCustomer();
cus.cusID=txtID.Text.ToString();
cus.LName = txtLName.Text.ToString();
cus.FName = txtFName.Text.ToString();
cus.Tel= txtTel.Text.ToString();
cus.Address = txtAddress.Text.ToString();
cus.Add();
}
catch(Exception err)
{
MessageBox.Show(err.Message.ToString());
}
}
//This function gets the ID from the user and finds the
//customer details and return the details in the form of
//a dataset via busniss object layer. Then it loops through
//the content of the dataset and fills the controls.
private void cmdFind_Click(object sender, System.EventArgs e)
{
try
{
String cusID = txtID.Text.ToString();
BOCustomer thisCus = new BOCustomer();
DataSet ds = thisCus.Find(cusID);
DataRow row;
row = ds.Tables[0].Rows[0];
//via looping
foreach(DataRow rows in ds.Tables[0].Rows )
{
txtFName.Text = rows["CUS_F_NAME"].ToString();
txtLName.Text = rows["CUS_L_NAME"].ToString();
txtAddress.Text = rows["CUS_ADDRESS"].ToString();
txtTel.Text = rows["CUS_TEL"].ToString();
}
}
catch (Exception err)
{
MessageBox.Show(err.Message.ToString());
}
}
//this function used to update the customer details.
private void cmdUpdate_Click(object sender,
System.EventArgs e)
{
try
{
cus = new BOCustomer();
cus.cusID=txtID.Text.ToString();
cus.LName = txtLName.Text.ToString();
cus.FName = txtFName.Text.ToString();
cus.Tel= txtTel.Text.ToString();
cus.Address = txtAddress.Text.ToString();
cus.Update();
}
catch(Exception err)
{
MessageBox.Show(err.Message.ToString());
}
}
Business Logic layer
Here, I am including all the code for this tier. Basically it has properties that are needed to define the customer object. But as I mentioned it is just a dummy customer and many other properties can be added if required. It also has all the methods including Add, update, find that are required to maintain customer details.
This is the middle tier and acts between the GUI and the Data access layer. It keeps a reference to the data access tier as cusData = new DACustomer(). It also has a reference to System.Data namespace as sometimes it returns details in the form of DataSet to the GUI tier.
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Copy Codeusing System;
using System.Data;
namespace _3tierarchitecture
{
///
/// Summary description for BOCustomer.
/// public class BOCustomer
{
//Customer properties
private String fName;
private String lName;
private String cusId;
private String address;
private String tel;
private DACustomer cusData;
public BOCustomer()
{
//An instance of the Data access layer!
cusData = new DACustomer();
}
///
/// Property FirstName (String)
/// public String FName
{
get
{
return this.fName;
}
set
{
try
{
this.fName = value;
if (this.fName == "")
{
throw new Exception(
"Please provide first name ...");
}
}
catch(Exception e)
{
throw new Exception(e.Message.ToString());
}
}
}
///
/// Property LastName (String)
/// public String LName
{
get
{
return this.lName;
}
set
{
//could be more checkings here eg revmove ' chars
//change to proper case
//blah blah
this.lName = value;
if (this.LName == "")
{
throw new Exception("Please provide name ...");
}
}
}
///
/// Property Customer ID (String)
/// public String cusID
{
get
{
return this.cusId;
}
set
{
this.cusId = value;
if (this.cusID == "")
{
throw new Exception("Please provide ID ...");
}
}
}
///
/// Property Address (String)
/// public String Address
{
get
{
return this.address;
}
set
{
this.address = value;
if (this.Address == "")
{
throw new Exception("Please provide address ...");
}
}
}
///
/// Property Telephone (String)
/// public String Tel
{
get
{
return this.tel;
}
set
{
this.tel = value;
if (this.Tel == "")
{
throw new Exception("Please provide Tel ...");
}
}
}
///
/// Function Add new customer. Calls
/// the function in Data layer.
/// public void Add()
{
cusData.Add(this);
}
///
/// Function Update customer details.
/// Calls the function in Data layer.
/// public void Update()
{
cusData.Update(this);
}
///
/// Function Find customer. Calls the
/// function in Data layer.
/// It returns the details of the customer using
/// customer ID via a Dataset to GUI tier.
/// public DataSet Find(String str)
{
if (str == "")
throw new Exception("Please provide ID to search");
DataSet data = null;
data = cusData.Find(str);
return data;
}
}
}
Data Access Layer
The data tier has details to manipulate an MS Access database. However, all these details are transparent and do not affect the business logic layer. This module has a reference to the business logic layer as BOCustomer cus. To make the usage easier and be supported by any other database I have created some constants including the database name and field name that need to be changed as per the customer table details. This is an usable module for any database after making these changes.
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Copy Codeusing System;
using System.Data.OleDb;
using System.Data;
namespace _3tierarchitecture
{
///
/// Summary description for DACustomer.
/// public class DACustomer
{
private OleDbConnection cnn;
//change connection string as per the
//folder you unzip the files
private const string CnnStr =
"Provider=Microsoft.Jet.OLEDB.4.0;Data " +
"Source= D:\\Rahman_Backup\\Programming\\" +
"Csharp\\3tierarchitecture\\customer.mdb;";
//local variables
private String strTable="";
private String strFields="";
private String strValues="";
private String insertStr="";
//this needs to be changed based on customer
//table fields' Name of the database!
private const String thisTable = "tblCustomer";
private const String cus_ID = "CUS_ID";
private const String cus_LName = "CUS_L_NAME";
private const String cus_FName = "CUS_F_NAME";
private const String cus_Tel = "CUS_TEL";
private const String cus_Address = "CUS_ADDRESS";
public DACustomer()
{
}
public DACustomer(BOCustomer cus)
{
// A reference of the business object class
}
//standard dataset function that adds a new customer
public void Add(BOCustomer cus)
{
String str = BuildAddString(cus);
OpenCnn();
//Open command option - cnn parameter is imporant
OleDbCommand cmd = new OleDbCommand(str,cnn);
//execute connection
cmd.ExecuteNonQuery();
// close connection
CloseCnn();
}
//standard dataset function that updates
//details of a customer based on ID
public void Update(BOCustomer cus)
{
OpenCnn();
String selectStr = "UPDATE " + thisTable +
" set " + cus_LName + " = '" + cus.LName + "'" +
", " + cus_FName + " = '" + cus.FName + "'" +
", " + cus_Address + " = '" + cus.Address + "'" +
", " + cus_Tel + " = '" + cus.Tel + "'" +
" where cus_ID = '" + cus.cusID + "'";
OleDbCommand cmd = new OleDbCommand(selectStr,cnn);
cmd.ExecuteNonQuery();
CloseCnn();
}
//standard dataset function that finds and
//return the detail of a customer in a dataset
public DataSet Find(String argStr)
{
DataSet ds=null;
try
{
OpenCnn();
String selectStr = "select * from " + thisTable +
" where cus_ID = '" + argStr + "'";
OleDbDataAdapter da =
new OleDbDataAdapter(selectStr,cnn);
ds = new DataSet();
da.Fill(ds,thisTable);
CloseCnn();
}
catch(Exception e)
{
String Str = e.Message;
}
return ds;
}
private void OpenCnn()
{
// initialise connection
String cnnStr = CnnStr;
cnn = new OleDbConnection(cnnStr);
// open connection
cnn.Open();
}
private void CloseCnn()
{
// 5- step five
cnn.Close();
}
// just a supporting function that builds
// and return the insert string for dataset.
private String BuildAddString(BOCustomer cus)
{
// these are the constants as
// set in the top of this module.
strTable="Insert into " + thisTable;
strFields=" (" + cus_ID +
"," + cus_LName +
"," + cus_FName +
"," + cus_Address +
"," + cus_Tel + ")";
//these are the attributes of the
//customer business object.
strValues= " Values ( '" + cus.cusID +
"' , '" + cus.LName +
"' , '" + cus.FName +
"' , '" + cus.Address +
"' , '" + cus.Tel + "' )";
insertStr = strTable + strFields + strValues;
return insertStr;
}
}
}
