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