Entity Framework框架 （一）

1. Entity Framework的详细介绍：

Entity Framework简称EF，与Asp.net关系与Ado.net关系。

Entity Framework是ado.net中的一组支持开发面向数据的软件应用程序的技术，是微软的一个ORM框架。

ORM：object relation mapping 是基于关系型数据库的数据储备，实现一个模拟的面向对象的数据访问接口，理想情况下，基于这样一个面向对象的接口，持久化一个oo对象应该不需要了解任何关系型数据库存储数据的实现细节。

类似的轻量级的orm框架，dapper，patapoct

 1. lambda表达式：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication1
{
    //定义一个委托
    public delegate int AddSum(int a,int b);
    class Program
    {
        static void Main(string[] args)
        {
            Program p = new Program();
           // AddSum addSum = new AddSum(p.Add);
           // AddSum addSum = delegate(int a, int b) { return a + b; };
            //AddSum addSum = (int a, int b) => { return a + b; };
            //简化之后的lambda表达式
            AddSum addSum = ( a,  b) => { return a + b; };
            int sum = addSum(5, 3);
            Console.WriteLine(sum);
            Console.ReadKey();
        }

        //public int Add(int a, int b)
        //{
        //    return a + b;
        //}
    }
    
}

一、第一种使用EF的方法：先有数据库再建立数据模型

 1. 在项目中右击新建，新建一个ADO.net实体数据模型，选择从数据库生成，这种是先有数据库再建立数据模型的方式。然后依次点击下一步便可，完成以后切记点击ctrl+s保存。不然是不会生成数据模型对应的类。

 2. 注意：对应的数据库表必须有主键，不然在使用时会报错。

 3. 生成之后的结构如下。 

 4.使用EF进行相关的增删改查代码如下:

 新建的web窗体页面，分别放四个button按钮便可。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace WebApplication2
{
    public partial class WebForm1 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {

        }
        /// <summary>
        /// 插入数据
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected void Button1_Click(object sender, EventArgs e)
        {
            UserInfo UserInfo = new UserInfo();
            UserInfo.UserName = "张五呀";
            UserInfo.UserPass = "123qwe";
            UserInfo.RegTime = 2;
            UserInfo.Email = "wangjin";
            AdwResourcesEntities1 db = new AdwResourcesEntities1();
            //将数据添加到EF中，并且添加了标记，并且类似于生成了一条insert语句，但是这时候还没有执行该语句
            db.UserInfo.Add(UserInfo);
            //之后执行该代码时，才会执行insert语句,并且返回受影响行数
            db.SaveChanges();
            //返回刚刚插入的主键ID
            Response.Write(UserInfo.ID);
        }
        /// <summary>
        /// 查询数据
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected void Button2_Click(object sender, EventArgs e)
        {
            AdwResourcesEntities1 db = new AdwResourcesEntities1();
            var userinfolist = from u in db.UserInfo   //linq表达式
                               where u.ID == 65 
                               select u;
            //EF的延迟加载机制，只有数据在使用的时候才会去数据库中查询，不用的时候不查询。
            //只有执行下面的代码的时候才会去执行，这样可以提高整体的性能
            foreach (var userinfo in userinfolist)
            {
                Response.Write(userinfo.ID);
            }
            //FirstOrDefault  查询第一条数据或者查询默认值
            //userinfolist.FirstOrDefault();
        }
        /// <summary>
        /// 删除数据
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected void Button3_Click(object sender, EventArgs e)
        {
            AdwResourcesEntities1 db = new AdwResourcesEntities1();
            var userinfolist = from u in db.UserInfo
                               where u.ID == 66
                               select u;
            //返回第一条数据，如果没有就放回null
            UserInfo userinfo = userinfolist.FirstOrDefault();
            if (userinfo != null)
            {
                db.UserInfo.Remove(userinfo);
                db.SaveChanges();
                Response.Write("删除成功");
            }
            else
            {
                Response.Write("数据有误");
            }
            
            ////执行删除的第二种方法
            //UserInfo userInfo = new UserInfo() {ID=344};
            db.Entry<UserInfo>(userinfo).State = System.Data.Entity.EntityState.Deleted;
            //db.SaveChanges();
        }

        /// <summary>
        /// 修改数据
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected void Button4_Click(object sender, EventArgs e)
        {
            //构建一个
            AdwResourcesEntities1 db = new AdwResourcesEntities1();
            var userinfolist = from u in db.UserInfo
                               where u.ID == 65
                               select u;
            UserInfo userinfo = userinfolist.FirstOrDefault();
            userinfo.UserPass = "qweqwe";
            db.Entry<UserInfo>(userinfo).State = System.Data.Entity.EntityState.Modified;
            db.SaveChanges();
            Response.Write("修改成功");
        }
    }
}

 

 二、第二种ModelFirst模式使用EF的方法，先建立数据模型，再生成数据库对应的表。

 1. 先在数据库中新建一个数据库。

 2.  在项目中右击新建项目，选择数据源，点击空模型。

 3. 在生成的空白界面中，右击新增实体，新增之后再新增标量属性，如果是多表，并且有关联的表，右击新增关联，再右击根据数据模型生成数据库。

 4. 点击如下文件，需要点击执行才会生成数据库。

 5. 使用第二种进行增删改查的相关代码如下：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace WebApplication1
{
    public partial class WebForm2 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {

        }
        /// <summary>
        /// 插入数据
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected void Button1_Click(object sender, EventArgs e)
        {
            Model2Container db = new Model2Container();
            Customer customer = new Customer() {CustomerName="zhangsan",CustomerPwd="123", SubTime=DateTime.Now };
            // Customer = customer导航属性，代表下面的数据属于上面的值
            OrderInfo orderInfo1 = new OrderInfo() { ID = Guid.NewGuid(), OrderNum = "10001", CreateDateTime = DateTime.Now,Customer=customer };
            OrderInfo orderInfo2 = new OrderInfo() { ID = Guid.NewGuid(), OrderNum = "10002", CreateDateTime = DateTime.Now, Customer = customer };
            db.Customer.Add(customer);
            db.OrderInfo.Add(orderInfo1);
            db.OrderInfo.Add(orderInfo2);
            db.SaveChanges();//默认的已经开启了事务。 工作单元模式。（UnitOfwork）
        }
        /// <summary>
        /// 查询数据
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected void Button2_Click(object sender, EventArgs e)
        {
            Model2Container db = new Model2Container();
            var customerList = from c in db.Customer
                               select c;
            foreach (var customer in customerList)
            {
                Response.Write(customer.CustomerName+":");


                foreach (var orderInfo in customer.OrderInfo)//延迟加载。
                {
                    Response.Write(orderInfo.OrderNum);
                }
            }
        }
        /// <summary>
        /// 根据名字id查询所有的订单
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected void Button3_Click(object sender, EventArgs e)
        {
            Model2Container db = new Model2Container();
            //var customerInfoList = from c in db.Customer
            //                   where c.ID == 1
            //                   select c;
            //var customerInfo = customerInfoList.FirstOrDefault();
            //foreach (var orderInfo in customerInfo.OrderInfo)
            //{
            //    Response.Write(orderInfo.OrderNum);
            //}

            var orderInfoList = from o in db.OrderInfo
                               where o.CustomerID == 1
                               select o;
            foreach (var orderInfo in orderInfoList)
            {
                Response.Write(orderInfo.OrderNum);
            }
                           
        }
        /// <summary>
        /// 输出10001对应的客户ID
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected void Button4_Click(object sender, EventArgs e)
        {
             Model2Container db = new Model2Container();
             var orderInfoList = from o in db.OrderInfo
                                 where o.OrderNum == "10001"
                                 select o;
             var orderInfo = orderInfoList.FirstOrDefault();
             Customer customer = orderInfo.Customer;
             Response.Write(customer.CustomerName);
        }
        /// <summary>
        /// 根据人员ID删除对应数据
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected void Button5_Click(object sender, EventArgs e)
        {
            Model2Container db = new Model2Container();
            //var customer = (from c in db.Customer
            //                where c.ID == 1
            //                select c).FirstOrDefault();
            //var orderInfoList = customer.OrderInfo;
            //while (orderInfoList.Count > 0)
            //{
            //    var orderInfo = orderInfoList.FirstOrDefault();
            //    db.Entry<OrderInfo>(orderInfo).State = System.Data.EntityState.Deleted;
            //}
            //db.SaveChanges();

            var orderList = from o in db.OrderInfo
                            where o.CustomerID == 2
                            select o;

        }

    }
}

 三、第三种codeFirst模式，该模式是指不建立数据模型，并且不建立建立数据库的情况下，通过代码的形式去新建一个数据库。

   1. ：创建实体类，并且给实体加上特性标签，并且标注一下实体类之间的关系。

     1.1创建classInfo(班级)实体类

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace CodeFirstDemo
{
   public class ClassInfo
    {
       [Key]  //特性标签
       public int Id { get; set; }
       [StringLength(32)]   //指定是字符串类型
       [Required]            //必填项
       public string ClassName { get; set; }
       [Required]
       public DateTime CreateTime { get; set; }
       //表示1对多，指一个班级对应多个学生
       public virtual ICollection<StudentInfo> StudentInfo { get; set; }
    }
}

  1.2 ：创建学生实体类

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace CodeFirstDemo
{
   public class StudentInfo
    {
       [Key]
       public int Id { get; set; }
       [StringLength(32)]
       [Required]
       public string StuName { get; set; }
        [Required]
       public DateTime SubTime { get; set; }
       public virtual ClassInfo ClassInfo { get; set; }  //表明外键关系，多对1
    }
}

1.3. 引用Entity

　　方法1，点击引用，system.data.Entity

　　方法2. 新建一个数据模型，之后删掉，此时已经自动引用了entity

1.4 ：创建codefirstdbcontext：dbcontext文件

　　

using System;
using System.Collections.Generic;
using System.Data.Entity;
using System.Data.Entity.ModelConfiguration.Conventions;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace CodeFirstDemo
{
   public class CodeFirstDbContext:DbContext
    {
       public CodeFirstDbContext()
           : base("name=connStr")  //对应连接数据库字符串的名字
       {

       }
       protected override void OnModelCreating(DbModelBuilder modelBuilder)
       {
           //此代码的功能是移除复数的约定  就是指生成的表名后面不加S
           modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
       }
        //对应的表
       public DbSet<ClassInfo> ClassInfo { get; set; }
       public DbSet<StudentInfo> StudentInfo { get; set; }
    }
}

1.5 ：在配置文件构建数据库链接字符串。

 <configSections>
2     <section name="entityFramework" type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=5.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />
3   </configSections>

 

1.6：查询部分数据以及实例创建代码

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace WebApplication1
{
    public partial class WebForm3 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {

        }
        /// <summary>
        /// 只查询其中几列数据
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected void Button1_Click(object sender, EventArgs e)
        {
            //使用HttpContext，只要持续调用，就一直都不会中断 
            EFFristModelEntities db = null;
            if (HttpContext.Current.Items["db"] == null)
            {
                db = new EFFristModelEntities();
                HttpContext.Current.Items["db"] = db;
            }
            else
            {
                db = HttpContext.Current.Items["db"] as EFFristModelEntities;
            }

           var userInfoList = from u in db.UserInfo
                               where u.ID == 343
                               select  new{UName=u.UserName,UPwd=u.UserPass};    //新建一个匿名类查询
            foreach (var userInfo in userInfoList)
            {
                Response.Write(userInfo.UName+":"+userInfo.UPwd);
            }

        }
        /// <summary>
        /// 匿名函数来查询
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected void Button2_Click(object sender, EventArgs e)
        {
          //  Func<UserInfo, bool> whereLambda = u => { return u.ID == 343; };
          
            EFFristModelEntities db = new EFFristModelEntities();
            //var userInfoList = db.UserInfo.Where<UserInfo>(u=>u.ID==3);
           
            //select * from UserInfo where id=343
            //升序排序
            //var userInfoList = db.UserInfo.Where<UserInfo>(U => true).OrderBy<UserInfo, int>(u => u.ID);
            //降序排序
         //var userInfoList = db.UserInfo.Where<UserInfo>(U => true).OrderByDescending(u => u.ID);

            int pageIndex = 2;
            int pageSize = 2;
            var userInfoList = (from u in db.UserInfo
                                where u.ID > 0
                                orderby u.RegTime ascending, u.ID descending
                                select u).Skip<UserInfo>((pageIndex - 1) * pageSize).Take<UserInfo>(pageSize);
         
      //   var userInfoList = db.UserInfo.Where<UserInfo>(U => true).OrderByDescending(u => u.UserPass).ThenByDescending<UserInfo, int>(u => u.ID);//Skip:表示跳过多少条记录, Take取多少条记录

      
            foreach (var userInfo in userInfoList)
            {
             
                    Response.Write(userInfo.UserName + "<br/>");
              
            }
        }

        protected void Button3_Click(object sender, EventArgs e)
        {
            string str ="ttttt";
          Response.Write (str.MyStr());
        }

        protected void Button4_Click(object sender, EventArgs e)
        {
            EFFristModelEntities db = new EFFristModelEntities();
          
            var userInfoList = db.UserInfo.Where<UserInfo>(u => u.ID >0);
        
            int i = 0;
            int count = userInfoList.Count();
            Response.Write(count);

        }
    }
}

以上就是EF创建和操作的详细介绍，欢迎评论和留言

 2：如果在.net core中启动ef的事务，具体如下：

     try
                {
                    using (var _activitydb = db.Database.BeginTransaction())
                    {
                        try
                        {
                            li.ForEach(o => o.IsMake = 1);
                            db.UpdateRange(li);
                            List<LogoNum> logolist = new List<LogoNum>();
                            for (int i = 0; i < isLogonum; i++)
                            {
                                LogoNum logo = new LogoNum();
                                logo.LogoNums = 1;
                                logo.UserId = userId;
                                logo.CreateTime = DateTime.UtcNow.AddHours(8);
                                logo.UserName = user.UserName;
                                logo.SiteId = siteId;
                                logolist.Add(logo);
                            }

                            db.LogoNum.AddRange(logolist);
                            int res = db.SaveChanges();
                            if (res < 1)
                            {
                                _activitydb.Rollback();
                                return -1;
                            }
                            _activitydb.Commit();
                            return isLogonum;
                        }
                        catch (Exception)
                        {
                            _activitydb.Rollback();
                            throw;
                        }
                    }
                }
                catch (Exception e)
                {
                    throw;
                }