使用EnterpriseLibrary5实现数据的缓存（附完整代码下载）

本例子演示了如何使用微软企业类库5.0实现数据的缓存。

本文代码下载

1，打开visual studio 2010，新建一个winform项目，并命名为CachingByEnterpriseLibrary5。

2，添加如下引用

• Microsoft.Practices.EnterpriseLibrary.Caching 　　（C:\Program Files\Microsoft Enterprise Library 5.0\Bin\Microsoft.Practices.EnterpriseLibrary.Caching.dll）
• Microsoft.Practices.EnterpriseLibrary.Common　　（C:\Program Files\Microsoft Enterprise Library 5.0\Bin\Microsoft.Practices.EnterpriseLibrary.Common.dll）
• Microsoft.Practices.ServiceLocation　　　　　　　  （C:\Program Files\Microsoft Enterprise Library 5.0\Bin\Microsoft.Practices.ServiceLocation.dll）

说明：EnterpriseLibrary5.0 下载地址

3，新增数据访问类 DataAccessLayer.cs，数据库使用的微软示例数据库Northwind。

using System;
using System.Collections.ObjectModel;
using System.Data.SqlClient;

namespace CachingByEnterpriseLibrary5
{

    public class Employee
    {
        public int Id { get; set; }
        public string LastName { get; set; }
        public string FirstName { get; set; }
        public string Title { get; set; }
        public DateTime BirthDate { get; set; }
        public string City { get; set; }
    }

    class DataAccess
    {
        SqlConnection Conn;
        SqlCommand Command;
        SqlDataReader Reader;

        public DataAccess()
        {
            Conn = new SqlConnection("Data Source=.;Initial Catalog=Northwind;Integrated Security=SSPI");
        }

        public ObservableCollection<Employee> GetEmployees()
        {
            ObservableCollection<Employee> lstEmployees = new ObservableCollection<Employee>();

            Conn.Open();
            Command = new SqlCommand();
            Command.Connection = Conn;
            Command.CommandText = "select * from Employees";
            Reader = Command.ExecuteReader();

            while (Reader.Read())
            {
                lstEmployees.Add(new Employee()
                {
                    Id = Convert.ToInt32(Reader["EmployeeID"]),
                    LastName = Reader["LastName"].ToString(),
                    FirstName = Reader["FirstName"].ToString(),
                    Title = Reader["Title"].ToString(),
                    BirthDate = Convert.ToDateTime(Reader["BirthDate"]),
                    City = Reader["City"].ToString()
                });
            }

            Reader.Close();
            Conn.Close();
            return lstEmployees;
        }
    }
}

4，增加数据缓存类CachingInfrastructure.cs

using System;
using System.Collections.ObjectModel;
using System.Linq;
using Microsoft.Practices.EnterpriseLibrary.Caching;
using Microsoft.Practices.EnterpriseLibrary.Caching.Expirations;
using Microsoft.Practices.EnterpriseLibrary.Common.Configuration;

namespace CachingByEnterpriseLibrary5
{
    public class CachingInfrastructure
    {
        static ObservableCollection<Employee> lstEmployee = null;
        static ICacheManager cacheEmployeeData;

        public CachingInfrastructure()
        {

        }

        public static ObservableCollection<Employee> GetEmployeeData(out string cacheStatus)
        {
            //尝试从缓存中读取数据
            cacheEmployeeData = EnterpriseLibraryContainer.Current.GetInstance<ICacheManager>();

            lstEmployee = (ObservableCollection<Employee>)cacheEmployeeData["EmployeeDataCache"];
            cacheStatus = "从缓存中读取全部员工数据";

            //如果缓存中没有任何数据，那么直接从数据访问层读取
            if (lstEmployee == null)
            {
                DataAccess da = new DataAccess();
                lstEmployee = da.GetEmployees();
                //定义缓存的有效期限（为了演示缓存效果，设置为10s）
                AbsoluteTime CacheExpiretionTime = new AbsoluteTime(new TimeSpan(0, 0, 10));
                //把数据放入缓存
                cacheEmployeeData.Add("EmployeeDataCache", lstEmployee, CacheItemPriority.High, null, new ICacheItemExpiration[] { CacheExpiretionTime });
                cacheStatus = "员工的信息刚被放入缓存中";
            }

            return lstEmployee;
        }

        public static Employee GetEmployeeById(int id, out string cacheStatus)
        {
            Employee emp = null;

            emp = (from e in lstEmployee
                   where e.Id == id
                   select e).FirstOrDefault();

            cacheStatus = "从缓存中读取指定id的员工信息";
            return emp;
        }

        public static void ClearCache(out string cacheStatus)
        {
            ICacheManager cacheEmployeeData = EnterpriseLibraryContainer.Current.GetInstance<ICacheManager>();
            cacheEmployeeData.Flush();
            cacheStatus = "缓存已被清空";
        }
    }
}

5,增加App.Config文件，然后右键该文件。

在弹出的对话框中选中 ‘Blocks’-> ‘Add Caching Settings’

6,Form1界面效果如下图所示

代码如下：

using System;
using System.Collections.ObjectModel;
using System.Windows.Forms;

namespace CachingByEnterpriseLibrary5
{
    public partial class Form1 : Form
    {
        ObservableCollection<Employee> lstEmployee = new ObservableCollection<Employee>();
        string cacheStauts = string.Empty;//缓存状态

        public Form1()
        {
            InitializeComponent();
        }

        //加载员工信息
        private void btnLoadData_Click(object sender, EventArgs e)
        {

            lstEmployee = CachingInfrastructure.GetEmployeeData(out cacheStauts);
            lblCacheStatus.Text = cacheStauts;

            foreach (var emp in lstEmployee)
            {
                cmbEmployee.Items.Add(new Item(emp.LastName, emp.Id));
            }

            cmbEmployee.DroppedDown = true;
            cmbEmployee.SelectedValueChanged += new System.EventHandler(cmbEmployee_SelectedIndexChanged);
        }

        //读取指定Id的员工信息
        private void cmbEmployee_SelectedIndexChanged(object sender, EventArgs e)
        {

            int Id = Convert.ToInt32(((Item)cmbEmployee.SelectedItem).Value);
            Employee Emp = CachingInfrastructure.GetEmployeeById(Id, out cacheStauts);

            lblCacheStatus.Text = cacheStauts;

            txtId.Text = Emp.Id.ToString();
            txtFirstName.Text = Emp.FirstName;
            txtLastName.Text = Emp.LastName;
            txtTitle.Text = Emp.Title;
            txtCity.Text = Emp.City;
            txtBirthDate.Text = Emp.BirthDate.ToShortDateString();
        }

        //手工清空缓存
        private void btnClearCache_Click(object sender, EventArgs e)
        {
            CachingInfrastructure.ClearCache(out cacheStauts);
            lblCacheStatus.Text = cacheStauts;

            cmbEmployee.Items.Clear();
            cmbEmployee.Text = "";

            txtId.Text = "";
            txtFirstName.Text = "";
            txtLastName.Text = "";
            txtTitle.Text = "";
            txtCity.Text = "";
            txtBirthDate.Text = "";

            lstEmployee.Clear();
        }

    }
}

为了手工控制ComboBox，添加自定义类文件Item.cs

namespace CachingByEnterpriseLibrary5
{
    //为了方便控制combobox，采用自定义类Item给combobox添加项目
    public class Item
    {
        public string Name;
        public int Value;

        public Item(string name, int value)
        {
            Name = name; Value = value;
        }

        public override string ToString()
        {
            // Generates the text shown in the combo box
            return Name;
        }
    }
}

7,如何验证是从缓存中读取的数据还是从数据库读取的数据？可以使用SQL Server的事件探查器来跟踪应用程序是否执行了相应的

SQL脚本来验证。打开事件探查器（sql server profiler）后，连续双击“加载数据“按钮即可！

看上图中两条被选中的记录间隔的时间正好10s，这也验证了下列代码

//定义缓存的有效期限（为了演示缓存效果，设置为10s）
AbsoluteTime CacheExpiretionTime = new AbsoluteTime(new TimeSpan(0, 0, 10));
//把数据放入缓存
cacheEmployeeData.Add("EmployeeDataCache", lstEmployee, CacheItemPriority.High, null, new ICacheItemExpiration[] { CacheExpiretionTime });