理解三层架构及其在 C# .NET 中的实现

• 下载源代码 - 41.1 KB
• 下载演示 - 9 KB

引言

为了有效地设计软件，我们倾向于采用多层架构。 这种方法已被业界采用，用于编写高效的代码。 在这种编码风格中，变更管理变得非常容易。 让我们简要讨论一下这种方法。 三层流程模型最初有助于我们高效工作。 一段时间后，如果业务逻辑发生任何变化，可以通过在特定层上进行特定更改来轻松完成。 例如，业务逻辑层的变化不会影响另外两层，即数据访问层和 UI。

这三层是如何连接的？

三层架构的数据流图

DAL 的实现

在实现 DAL 之前，您首先需要了解什么是 DAL 或数据访问层，以及它包含什么。

在数据访问层中，数据可以是任何数据库（Oracle、SQL Server、Access、PostgreSQL、MySQL 等）或任何文件。 也就是说，您存储数据的地方。 并且这一层是您的应用程序与该数据之间唯一的连接。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.SqlClient;
using System.Data;
 
namespace DAL
// Notice this name of this namespace. In BLL we will use
// this 'DAL' namespace according to the above picture
{
    class Database
    {
        internal string UserName { get; set; }
 
        internal string Password { get; set; }
 
        internal string ServerName { get; set; }
 
        internal string DatabaseName { get; set; }
 
        internal string ConnectionString
        {
            get { return "Data Source=" + ServerName + ";Initial Catalog=" + 
              DatabaseName + ";Persist Security Info=True;User ID=" + 
              UserName + ";Password=" + Password; }
        }
 
        /// <summary>
        /// Insert, Update and Delete in the database through this method
        /// </summary>
        /// The SQL Query or the name of the Stored Procedure
        /// The values which you have to insert, update, or delete
        /// If the first parameter "sql"
        /// is any name of the stored procedure then it must be true
        /// True for successful execution, otherwise False
        public bool InsertUpdateDelete(string sql, Dictionary parameters, bool isProcedure)
        {
            using (SqlConnection sqlConnection = new SqlConnection(ConnectionString))
            {
                sqlConnection.Open();
 
                using (SqlCommand sqlCommand = new SqlCommand(sql, sqlConnection))
                {
                    if (isProcedure)
                        sqlCommand.CommandType = 
                           System.Data.CommandType.StoredProcedure;
                    else sqlCommand.CommandType = System.Data.CommandType.Text;
 
                    // Adding parameters using Dictionary...
                    foreach (KeyValuePair parameter in parameters)
                        sqlCommand.Parameters.Add(new SqlParameter(parameter.Key, parameter.Value));
                    if (sqlCommand.ExecuteNonQuery() > 0) return true;
                    else return false;
                }
            }
        }
 
        /// <summary>
        /// Select from database through this method
        /// </summary>
        /// The SQL Query or the name of the Stored Procedure
        /// If the first parameter "sql" is any name of the stored procedure then it must be true
        /// The parameters which you want to pass through WHERE clause in SELECT Query
        /// The resultant table aganist the select query or the stored procedure
        public DataTable Select(string sql, bool isProcedure, Dictionary parameters = null)
        {
            using (SqlConnection sqlConnection = new SqlConnection(ConnectionString))
            {
                sqlConnection.Open();
                using (SqlCommand sqlCommand = new SqlCommand(sql, sqlConnection))
                {
                    if (isProcedure) sqlCommand.CommandType = CommandType.StoredProcedure;
                    else sqlCommand.CommandType = CommandType.Text;
                    if (parameters != null)
                        foreach (KeyValuePair parameter in parameters)
                            sqlCommand.Parameters.Add(new SqlParameter(parameter.Key, parameter.Value));
                    using (SqlDataAdapter sqlDataAdapter = new SqlDataAdapter(sqlCommand))
                    {
                        using (DataTable dt = new DataTable())
                        {
                            sqlDataAdapter.Fill(dt);
                            return dt;
                        }
                    }
                }
            }
        }
    }
}

BLL 的实现

在实现 BLL 之前，您首先需要了解什么是 BLL 或业务逻辑层，以及它包含什么。

粗略地说，您可以将“表名”视为“类名”，“列名”视为“数据成员或属性的名称”，并将 DDL 和 DML 操作视为该类的方法。

让我们来实现我所说的内容

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;
using DAL;    // Notice this as I've already told you, I'm doing accordingly...

namespace BLL
{
    class EmployeeBLL
    {
        /* This properties are the columns of the table 'Employee' */
        public long EmployeeId { get; set; }
        public string EmployeeName { get; set; }
        public string EmployeeAddress { get; set; }
        public double Salary { get; set; }
        public DateTime DOJ { get; set; }
 
        
        /* I've just implement four basic database operations: Insert, Update, Delete, Select */
 
        public bool InsertEmployee()
        {
            Database db = InitializeDatabase();
 
            string sqlQuery = "INSERT INTO [Employee] ";
            sqlQuery += "(EmployeeName, EmployeeAddress, Salary, DOJ) ";
            sqlQuery += "VALUES ";
            sqlQuery += "(@EmployeeName, @EmployeeAddress, @Salary, @DOJ)";
 
            Dictionary parameters = new Dictionary();
            parameters.Add("@EmployeeName", EmployeeName);
            parameters.Add("@EmployeeAddress", EmployeeAddress);
            parameters.Add("@Salary", Salary);
            parameters.Add("@DOJ", DOJ);
 
            return db.InsertUpdateDelete(sqlQuery, parameters, false);
        }
 
        public bool UpdateEmployee()
        {
            Database db = InitializeDatabase();
 
            string sqlQuery = "UPDATE [Employee] SET ";
            sqlQuery += "EmployeeName=@EmployeeName, EmployeeAddress=@EmployeeAddress, Salary=@Salary, DOJ=@DOJ ";
            sqlQuery += "WHERE EmployeeId=@EmployeeId";
 
            Dictionary parameters = new Dictionary();
            parameters.Add("@EmployeeId", EmployeeId);
            parameters.Add("@EmployeeName", EmployeeName);
            parameters.Add("@EmployeeAddress", EmployeeAddress);
            parameters.Add("@Salary", Salary);
            parameters.Add("@DOJ", DOJ);
 
            return db.InsertUpdateDelete(sqlQuery, parameters, false);
        }
 
        public bool DeleteEmployee()
        {
            Database db = InitializeDatabase();
 
            string sqlQuery = "DELETE [Employee] WHERE EmployeeId=@EmployeeId";
 
            Dictionary parameters = new Dictionary();
            parameters.Add("@EmployeeId", EmployeeId);
 
            return db.InsertUpdateDelete(sqlQuery, parameters, false);
        }
 
        public DataTable SelectEmployee()
        {
            Database db = InitializeDatabase();
            
            string sqlQuery = "SELECT EmployeeId AS Id, EmployeeName AS Name, " + 
              "EmployeeAddress AS Address, Salary, DOJ AS 'Joining Date' FROM Employee";
 
            return db.Select(sqlQuery, false);
        }
 
        public DataRow SelectEmployeeById()
        {
            Database db = InitializeDatabase();
            
            string sqlQuery = "SELECT EmployeeName AS Name, EmployeeAddress " + 
              "AS Address, Salary, DOJ AS 'Joining Date' ";
            sqlQuery += "FROM Employee WHERE EmployeeId=@EmployeeId";
 
            Dictionary parameters = new Dictionary();
            parameters.Add("@EmployeeId", EmployeeId);
 
            return db.Select(sqlQuery, false, parameters).AsEnumerable().First();
        }
 
        private Database InitializeDatabase()
        {
            Database db = new Database();
            db.UserName = "sa";
            db.Password = "server2008";
            db.ServerName = "(local)";
            db.DatabaseName = "DebopamDB";
            return db;
        }
    }
}

UI 层的实现

UI 层是用户界面层。 这一层包含基于 Web 的应用程序的 Web 表单及其控件。 以及基于桌面应用程序的 Windows 表单及其控件。

我实现了一个基于桌面的应用程序演示。 在下一个版本中，我将向您展示如何使用我在这里实现的相同 DAL 和 BLL 来实现基于 Web 的应用程序。

主窗体

主窗体后面

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using BLL;
// Notice this, I'm using the namespace of BLL, not DAL as described above.

namespace ThreeLayerArchitectureDemo
{
    public partial class FormManageEmployee : Form
    {
        EmployeeBLL employee = new EmployeeBLL();
 
        public FormManageEmployee()
        {
            InitializeComponent();
        }
 
        private void FormManageEmployee_Load(object sender, EventArgs e)
        {
            FillGridView();
        }
 
        // Code aganist 'Insert' button
        private void btnInsert_Click(object sender, EventArgs e)
        {
            using (FormEditUpdateEmployee frmEditUpdateEmp = new FormEditUpdateEmployee())
            {
                frmEditUpdateEmp.EmployeeId = 0;
                if (frmEditUpdateEmp.ShowDialog() == System.Windows.Forms.DialogResult.OK)
                {
                    employee = frmEditUpdateEmp.ToEmployee();
                    if (employee.InsertEmployee())
                    {
                        FillGridView();
                        MessageBox.Show("Successfully Inserted", "Success", 
                          MessageBoxButtons.OK, MessageBoxIcon.Information);
                    }
                    else
                        MessageBox.Show("Error during Inserting", "Error", 
                          MessageBoxButtons.OK, MessageBoxIcon.Error);
                }
                else return;
            }
        }
 
        private void FillGridView()
        {
            grdViewEmployee.DataSource = employee.SelectEmployee();
        }
 
        // Code aganist 'Edit' button
        private void btnEdit_Click(object sender, EventArgs e)
        {
            using (FormEditUpdateEmployee frmEditUpdateEmp = new FormEditUpdateEmployee())
            {
                frmEditUpdateEmp.EmployeeId = long.Parse(grdViewEmployee.CurrentRow.Cells["Id"].Value.ToString());
                if (frmEditUpdateEmp.ShowDialog() == System.Windows.Forms.DialogResult.OK)
                {
                    employee = frmEditUpdateEmp.ToEmployee();
                    if (employee.UpdateEmployee())
                    {
                        FillGridView();
                        MessageBox.Show("Successfully Updated", 
                          "Success", MessageBoxButtons.OK, MessageBoxIcon.Information);
                    }
                    else
                        MessageBox.Show("Error during Updating", 
                          "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
                }
                else
                    return;
            }
        }
 
        // Code aganist 'Delete' button
        private void btnDelete_Click(object sender, EventArgs e)
        {
            employee.EmployeeId = long.Parse(grdViewEmployee.CurrentRow.Cells["Id"].Value.ToString());
            employee.EmployeeName = grdViewEmployee.CurrentRow.Cells["Name"].Value.ToString();
            if (MessageBox.Show("Delete " + employee.EmployeeName + "?", 
                  "Delete Employee?", MessageBoxButtons.YesNo, 
                  MessageBoxIcon.Question) == System.Windows.Forms.DialogResult.Yes)
                if (employee.DeleteEmployee())
                {
                    FillGridView();
                    MessageBox.Show("Successfully Deleted", 
                      "Success", MessageBoxButtons.OK, MessageBoxIcon.Information);
                }
                else
                    MessageBox.Show("Error during Deleting", 
                      "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
            else
                return;
        }
    }
}

插入/编辑窗体

插入/编辑窗体后面

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using BLL;
 
namespace ThreeLayerArchitectureDemo
{
    public partial class FormEditUpdateEmployee : Form
    {
        EmployeeBLL employee = new EmployeeBLL();
 
        public long EmployeeId
        {
            get { return long.Parse(this.txtName.Tag.ToString()); }
            set
            {
                if (value == 0)
                {
                    this.txtName.Text = null;
                    this.txtName.Tag = 0;
                    this.txtAddress.Text = null;
                    this.txtSalary.Text = null;
                    this.dateDOJ.Value = DateTime.Today.Date;
                }
                else
                {
                    employee.EmployeeId = value;
                    DataRow dr = employee.SelectEmployeeById();
                    this.txtName.Text = dr["Name"].ToString();
                    this.txtName.Tag = value;
                    this.txtAddress.Text = dr["Address"].ToString();
                    this.txtSalary.Text = dr["Salary"].ToString();
                    this.dateDOJ.Value = DateTime.Parse(dr["Joining Date"].ToString());
                }
            }
        }
 
        internal EmployeeBLL ToEmployee()
        {
            employee.EmployeeId = long.Parse(this.txtName.Tag.ToString());
            employee.EmployeeName = this.txtName.Text;
            employee.EmployeeAddress = this.txtAddress.Text;
            employee.Salary = double.Parse(this.txtSalary.Text);
            employee.DOJ = this.dateDOJ.Value;
            return employee;
        }
 
        public FormEditUpdateEmployee()
        {
            InitializeComponent();
        }
 
        // Code aganist 'Save' button
        private void btnSave_Click(object sender, EventArgs e)
        {
            this.DialogResult = System.Windows.Forms.DialogResult.OK;
            this.Close();
        }
 
        // Code aganist 'Cancel' button
        private void btnCancel_Click(object sender, EventArgs e)
        {
            this.DialogResult = System.Windows.Forms.DialogResult.Cancel;
            this.Close();
        }
    }
}

使用三层架构的优点

• 可扩展性：应用程序服务器可以部署在许多机器上，数据库不再需要来自每个客户端的连接。
• 可重用性：您可以使用不同的用户界面（如 ASP.NET Web Form、ASP.NET Web Service、.NET Window Form 等）来重用业务逻辑层 (BLL)，即中间层。 您可以重用数据库访问层 (DAL)，即具有不同项目的顶层。
• 改进数据完整性：BLL（即中间层）可以确保只允许在数据库中插入、更新或删除有效数据。
• 提高安全性：由于客户端无法直接访问数据库。 BLL 通常更安全，因为它位于更安全的中央服务器上。
• 减少分发：对 BLL/DLL 的更改只需在应用程序服务器上更新，不必分发给所有客户端。
• 隐藏数据库结构：由于数据库的实际结构对用户隐藏。
• 提高可用性

使用三层架构的缺点

• 增加开发人员的复杂性和工作量
• 一般来说，与两层架构相比，三层架构构建起来更复杂
• 通信点加倍

关注点

当您实现此代码时，您还将学习在 C# 中使用 Dictionary、using 和 internal。

历史

• 版本 1.0：2013 年 11 月。