在C#中實現3層架構

來源: 中國論壇網發布時間: 2009-10-23 11:59 閱讀: 1417 次推薦: 0 [收藏]

　　這篇文章討論如何在c＃中實現3層架構，使用MS Access數據庫存儲數據。在此，我在3層架構中實現一個小型的可復用的組件保存客戶數據。并提供添加，更新，查找客戶數據的功能。

　　背景

　　首先，我介紹一些3層架構的理論知識。簡單說明：什么是3層架構？3層架構的優點是什么？

　　什么是3層架構？

　　3層架構是一種“客戶端－服務器”架構，在此架構中用戶接口，商業邏輯，數據保存以及數據訪問被設計為獨立的模塊。主要有3個層面，第一層（表現層，GUI層），第二層（商業對象，商業邏輯層），第三層（數據訪問層）。這些層可以單獨開發，單獨測試。

　　為什么要把程序代碼分為3層。把用戶接口層，商業邏輯層，數據訪問層分離有許多的優點。

　　在快速開發中重用商業邏輯組件，我們已經在系統中實現添加，更新，刪除，查找客戶數據的組件。這個組件已經開發并且測試通過，我們可以在其他要保存客戶數據的項目中使用這個組件。

　　系統比較容易遷移，商業邏輯層與數據訪問層是分離的，修改數據訪問層不會影響到商業邏輯層。系統如果從用SQL Server存儲數據遷移到用Oracle存儲數據，并不需要修改商業邏輯層組件和GUI組件

　　系統容易修改，假如在商業層有一個小小的修改，我們不需要在用戶的機器上重裝整個系統。我們只需要更新商業邏輯組件就可以了。

　　應用程序開發人員可以并行，獨立的開發單獨的層。

　　代碼

　　這個組件有3層，第一個層或者稱為GUI層用form實現，叫做FrmGUI。第二層或者稱為商業邏輯層，叫做BOCustomer，是Bussniess Object Customer的縮寫。最后是第三層或者稱為數據層，叫做DACustomer，是Data Access Customer的縮寫。為了方便，我把三個層編譯到一個項目中。

　　用戶接口層

　　下面是用戶接口成的一段代碼，我只選取了調用商業邏輯層的一部分代碼。

//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());
    }
}

　　商業邏輯層

　　下面是商業邏輯層的所有代碼，主要包括定義customer對象的屬性。但這僅僅是個虛構的customer對象，如果需要可以加入其他的屬性。商業邏輯層還包括添加，更新，查找，等方法。

　　商業邏輯層是一個中間層，處于GUI層和數據訪問層中間。他有一個指向數據訪問層的引用cusData = new DACustomer().而且還引用了System.Data名字空間。商業邏輯層使用DataSet返回數據給GUI層。

using 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;
                }
    }
}

　　數據訪問層

　　數據層包括處理MS Access數據庫的細節。所有這些細節都是透明的，不會影響到商業邏輯層。數據訪問層有個指向商業邏輯層的引用BOCustomer cus。為了應用方便并且支持其他數據庫。

using 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;          
                    }
        }
}