Entity FrameWork 增删改查

     Entity Framework (又称ADO.NET Entity Framework) 是微软以 ADO.NET 为基础所发展出来的对象关系对应(O/R Mapping) 解决方案

    *新增

 方法一：

//实例化添加的对象

Employees employees = new Employees { FirstName="zhou",LastName="quan", Title="Manager"};


#region ef添加数据

 using (var db = new NorthwindEntities())
 {

    db.Employees.Add(employees);
    db.SaveChanges();

  }

 #endregion

  方法二：

//添加引用
  using System.Data.Entity.Infrastructure;

//实例化添加的对象

  Employees employees = new Employees { FirstName="zhou",LastName="quan", Title="Manager"};


  #region ef添加数据

  using (var db = new NorthwindEntities())
  {


      DbEntityEntry<Employees> enty = db.Entry<Employees>(employees);
      enty.State = System.Data.Entity.EntityState.Added;
      db.SaveChanges();
               
 }
 #endregion　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　

  *修改

 方法一：

#region ef修改数据(官方推荐，先查询，在修改)

 using (var db = new NorthwindEntities())
 {

    Employees employees = db.Employees.Where(r => r.EmployeeID == 1).FirstOrDefault();
    if (employees != null)
    {


       employees.FirstName = "zhou";
       employees.LastName = "quan";
       db.SaveChanges();


      }

  }

#endregion

　方法二：

//添加引用
 using System.Data.Entity.Infrastructure;

#region ef修改数据(修改整个实体，所有字段都会修改，其他没有值的都会为空NULL)
/定义修改的数据
 Employees employees = new Employees { EmployeeID = 1, FirstName = "zhou", LastName = "quan" };
 using (var db = new NorthwindEntities())
 {

     DbEntityEntry<Employees> entry = db.Entry<Employees>(employees);
     entry.State = System.Data.Entity.EntityState.Modified;
     db.SaveChanges();
 }

#endregion

 注意：上面这个方法会修改整个实体所有字段的数据，没有初始化值的字段会默认给空

 上面的方法一可以与方法二结合，这个代码就略了

例如sql如下：

exec sp_executesql N'UPDATE [dbo].[Employees]
SET [LastName] = @0, [FirstName] = @1, [Title] = NULL, [TitleOfCourtesy] = NULL, [BirthDate] = NULL, [HireDate] = NULL, [Address] = NULL, [City] = NULL, [Region] = NULL, [PostalCode] = NULL, [Country] = NULL, [HomePhone] = NULL, [Extension] = NULL, [Photo] = NULL, [Notes] = NULL, [ReportsTo] = NULL, [PhotoPath] = NULL
WHERE ([EmployeeID] = @2)
',N'@0 nvarchar(20),@1 nvarchar(10),@2 int',@0=N'quan',@1=N'zhou',@2=1

方法三：

//添加引用
 using System.Data.Entity.Infrastructure;

 #region ef修改数据
 //定义修改的数据
 Employees employees = new Employees { EmployeeID = 1, FirstName = "zhou", LastName = "quan" };
 using (var db = new NorthwindEntities())
 {

     //将对象加入EF容器，并获取当前实体对象的状态管理对象
     DbEntityEntry<Employees> entry = db.Entry<Employees>(employees);
     //设置该对象为被修改为
     entry.State = System.Data.Entity.EntityState.Unchanged;
     //设置属性是否修改
     entry.Property("FirstName").IsModified = true;
     entry.Property("LastName").IsModified = true;
     db.SaveChanges();
   }

#endregion

　*删除

   方法一：

//添加引用
 using System.Data.Entity.Infrastructure;

#region ef删除数据
 //定义数据
  Employees employees = new Employees { EmployeeID = 1};
  using (var db = new NorthwindEntities())
  {
         DbEntityEntry<Employees> entry = db.Entry<Employees>(employees);
         entry.State = System.Data.Entity.EntityState.Deleted;
          db.SaveChanges();

  }

  #endregion

　方法二：

 #region ef删除数据
   //定义数据
    Employees employees = new Employees { EmployeeID = 1};
    using (var db = new NorthwindEntities())
    {
         //附加要删除的对象到ef
          db.Employees.Attach(employees);
         //标记为删除--注意：标记为删除状态
          db.Employees.Remove(employees);
          db.SaveChanges();

     }
   #endregion

　方法三（先查询，再删除）：

  #region ef删除数据
  using (var db = new NorthwindEntities())
 {
     var employees = db.Employees.Where(r => r.EmployeeID == 1).FirstOrDefault();
     if (employees!=null)
     {
        db.Employees.Remove(employees);
        db.SaveChanges();
      }

   }

   #endregion

  *查询

     简单查询：

 #region ef查询数据

  using (var db = new NorthwindEntities())
 {
    //Linq查询
    var result = from p in db.Employees where p.City=="上海"&&p.Title.Contains("上海") orderby p.EmployeeID ascending,p.FirstName descending select new { Name=p.FirstName,Address=p.Address};

    //方法查询
    var _result = db.Employees.Where(r => r.City == "上海" && r.Title.Contains("上海")).OrderBy(r => r.EmployeeID).OrderByDescending(r => r.FirstName).Select(r => new { Name = r.FirstName, Address = r.Address });


   }

    #endregion