.net中实现简单三层架构

这篇文章讨论如何在.net中实现3层架构，使用MS sqlserver2005数据库存储数据。在此，我在3层架构中实现一个小型的可复用的组件保存客户数据。并提供添加，更新，查找客户数据的功能。

什么是3层架构？

3层架构是一种“客户端－服务器”架构，在此架构中用户接口，商业逻辑，数据保存以及数据访问被设计为独立的模块。主要有3个层面，第一层（表现层，GUI层），第二层（商业对象，商业逻辑层），第三层（数据访问层）。这些层可以单独开发，单独测试。

为什么要把程序代码分为3层。把用户接口层，商业逻辑层，数据访问层分离有许多的优点。

在快速开发中重用商业逻辑组件，我们已经在系统中实现添加，更新，删除，查找客户数据的组件。这个组件已经开发并且测试通过，我们可以在其他要保存客户数据的项目中使用这个组件。

系统比较容易迁移，商业逻辑层与数据访问层是分离的，修改数据访问层不会影响到商业逻辑层。系统如果从用SQL Server存储数据迁移到用Oracle存储数据，并不需要修改商业逻辑层组件和GUI组件

系统容易修改，假如在商业层有一个小小的修改，我们不需要在用户的机器上重装整个系统。我们只需要更新商业逻辑组件就可以了。

应用程序开发人员可以并行，独立的开发单独的层。

代码

这个组件有3层，第一个层或者称为GUI层用aspx页面实现，叫做defalt.aspx。第二层或者称为商业逻辑层，叫做BOEmployee，是Bussniess Object Employee的缩写。最后是第三层或者称为数据层，叫做DAEmployee，是Data Access Employee的缩写。

用户接口层(表示层default.cs代码)

下面是用户接口成的一段代码，我只选取了调用商业逻辑层的一部分代码。

public partial class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{ }

}
protected void ButtonAdd_Click(object sender, EventArgs e)
{
BOEmployee employee = new BOEmployee();
employee.EmployeeId = TextBoxEmployeeID.Text;
employee.FirstName = TextBoxFirstName.Text;
employee.LastName = TextBoxLastName.Text;
employee.HomePhone = TextBoxHomePhone.Text;
employee.Address = TextBoxAddress.Text;
employee.Add();
}
protected void ButtonFind_Click(object sender, EventArgs e)
{
BOEmployee employee = new BOEmployee();
string str = TextBoxFind.Text;

DataSet ds = new DataSet();
ds=employee.Find(str);

foreach( DataRow row in ds.Tables[0].Rows)
{
TextBoxEmployeeID.Text = row["EmployeeID"].ToString();
TextBoxFirstName.Text = row["FirstName"].ToString();
TextBoxLastName.Text = row["LastName"].ToString();
TextBoxAddress.Text = row["Address"].ToString();
TextBoxHomePhone.Text=row["HomePhone"].ToString();
}

}
protected void ButtonUpdate_Click(object sender, EventArgs e)
{
BOEmployee employee = new BOEmployee();
employee.EmployeeId = TextBoxFind.Text;
employee.FirstName = TextBoxFirstName.Text;
employee.LastName = TextBoxLastName.Text;
employee.HomePhone = TextBoxHomePhone.Text;
employee.Address = TextBoxAddress.Text;
employee.Update();
}
}

商业逻辑层

下面是商业逻辑层的所有代码，主要包括定义Employee对象的属性。但这仅仅是个虚构的Employee对象，如果需要可以加入其他的属性。商业逻辑层还包括添加，更新，查找，等方法。

商业逻辑层是一个中间层，处于GUI层和数据访问层中间。他有一个指向数据访问层的引用 employee = new DAEmployee().而且还引用了System.Data名字空间。商业逻辑层使用DataSet返回数据给GUI层

以下是实现商业逻辑层的代码:

/// <summary>
/// BOEmployee 的摘要说明
/// </summary>
namespace _3tierarchitecture
{
public class BOEmployee
{
public BOEmployee()
{
//
// TODO: 在此处添加构造函数逻辑

//An instance of the Data access layer!
employee = new DAEmployee();
}
//Employee property
private string firstName;
private string lastName;
private string homePhone;
private string address;
private DAEmployee employee;

//Employee Field
public string Address
{
get { return this.address; }
set
{
this.address = value;
if (this.address == "")
throw new Exception("please provide address");

}
}

public string HomePhone
{
get { return this.homePhone; }
set
{
this.homePhone = value;
if (this.homePhone == "")
throw new Exception("please provide homePhone");

}
}
private string employeeId;

public string EmployeeId
{
get { return this.employeeId; }
set
{
this.employeeId = value;
if (this.employeeId == "")
throw new Exception("please provide employeeid");
}
}

public string FirstName
{
get
{
return this.firstName;
}
set
{

this.firstName = value;
if (this.firstName == "")
throw new Exception("please provide firstname");

}

}

public string LastName
{
get { return this.lastName; }
set
{
this.lastName = value;
if (this.lastName == "")
throw new Exception("please provide lastname");

}
}

/// <SUMMARY>

/// Function Add new employee. Calls

/// the function in Data layer.

/// </SUMMARY>
public void Add()
{
employee.Add(this);

}
///<SUMMARY>
///Function Update new employee calls
///the function in data layer
///</SUMMARY>
public void Update()
{
employee.Update(this);

}
///<SUMMARY>
/// function in Data layer.

/// It returns the details of the customer using

/// customer ID via a Dataset to GUI tier.
/// </SUMMARY>
public DataSet Find(string str)
{
if (str == "")
throw new Exception("Please provide Employeeid");
DataSet ds = new DataSet();
ds=employee.Find(str);
return ds;

}

}
}
数据访问层

数据层包括处理MS sqlserver 2005数据库的细节。所有这些细节都是透明的，不会影响到商业逻辑层。数据访问层有个指向商业逻辑层的引用BOEmployee employee。为了应用方便并且支持其他数据库。

/// <summary>
/// DACustomer 的摘要说明
/// </summary>
namespace _3tierarchitecture
{
public class DAEmployee
{
//数据库连接
private SqlConnection myConnection=new SqlConnection(ConfigurationManager.ConnectionStrings["SqlConnectionString"].ConnectionString);
public DAEmployee()
{
//
// TODO: 在此处添加构造函数逻辑
//
}
private string strTable = "";
private string strFields = "";
private string strValues = "";
private string strInsert = "";

private const string thisTabel = "Employees";
private const string employeeId = "EmployeeID";
private const string lastName = "LastName";
private const string firstName = "FirstName";
private const string address = "Address";
private const string homePhone = "HomePhone";

//增记录语句
private string BuildAddString(BOEmployee employee)
{
// these are the constants as
// set in the top of this module.
strTable = "Insert into " + thisTabel;

strFields = " (" + employeeId +

"," + firstName+

"," + lastName +

"," + address +

"," + homePhone + ")";

//these are the attributes of the

//customer business object.

strValues = " Values ( '" + employee.EmployeeId +

"' , '" + employee.FirstName +

"' , '" + employee.LastName +

"' , '" + employee.Address +

"' , '" + employee.HomePhone + "' )";

strInsert = strTable + strFields + strValues;

return strInsert;

}
/// <summary>
/// 增加一个数据记录
/// </summary>
/// <param name="employee"></param>
public void Add(BOEmployee employee)
{
string str = BuildAddString(employee);

SqlCommand myCommand = new SqlCommand(str,myConnection);
ConOpen();
myCommand.ExecuteNonQuery();

ConClose();

}
///<summary>
///更新一个记录
///</summary>
public void Update(BOEmployee employee)
{
//打开数据库

string updateString = "update " + thisTabel + " set " + firstName + "='" + employee.FirstName + "'," + lastName + "='" + employee.LastName + "'," + address + "='" + employee.Address + "'," + homePhone + "='" + employee.HomePhone + "' where " +
employeeId + "='" + employee.EmployeeId+"'";
SqlCommand myCommand = new SqlCommand(updateString,myConnection);
ConOpen();
myCommand.ExecuteNonQuery();

//关闭数据库
ConClose();

}

///<summary>
/// 查找一个记录
///</summary>
public DataSet Find(string argStr)
{
DataSet ds = null;

string selectStr = "select * from " + thisTabel + " where employeeId= '" + argStr + "'";

//SqlCommand myCommand = new SqlCommand(selectStr,myConnection);
ds = new DataSet();
//打开数据库
ConOpen();
SqlDataAdapter da = new SqlDataAdapter(selectStr,myConnection);
da.Fill(ds,thisTabel);

//关闭数据库
ConClose();
return ds;

}

//打开数据库连接
public void ConOpen()
{
myConnection.Open();
}
//关闭数据库连接
public void ConClose()
{
myConnection.Close();
}

}
}