entity framework增删改查简单操作

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

namespace myAppLearnEntity
{
class Program
{
static void Main(string[] args)
{
//（1）添加实体对象数据到数据库
//TestEntities test = new TestEntities();

//Book book = new Book();
//book.Name = "test111";

//test.Book.AddObject(book);
//test.SaveChanges();

//（2）修改实体对象数据同步到数据库

/*
TestEntities test = new TestEntities();

Book book = new Book();
book.ID = 1;
book.Name = "test100";

test.Book.Attach(book);
test.ObjectStateManager.ChangeObjectState(book, System.Data.EntityState.Modified);

test.SaveChanges();
*/

//（3）删除实体对象数据同步到数据库
/*
TestEntities test = new TestEntities();

Book book = new Book();
book.ID = 3;
//book.Name = "test100";

test.Book.Attach(book);
test.ObjectStateManager.ChangeObjectState(book, System.Data.EntityState.Deleted);

test.SaveChanges();
*/

//（4）查询数据(查询多条语句)

//TestEntities test = new TestEntities();
//var datas = from c in test.Book
// where c.ID < 5
// select c;

//foreach (var item in datas)
//{
// Console.WriteLine(item.Name);
//}

//（5）查询数据(查询单条语句)
TestEntities test = new TestEntities();

//写法一
//var datas = (from c in test.Book
// where c.ID == 5
// select c).SingleOrDefault();

  //写法二
//var datas = (from c in test.Book
// where c.ID == 2
// select c).FirstOrDefault();

//if (datas!=null)
//{
// Console.WriteLine(datas.Name);
//}

//（6）级联查询

TestEntities test = new TestEntities();

var list = ( from b in test.Book
join s in test.Student
on b.StudentID equals s.ID into userrooms

from ur in userrooms.DefaultIfEmpty()

select new
{
id=ur.ID,
name=ur.Name
}).ToList();

foreach (var item in list)
{
Console.WriteLine(item.name);
}

Console.ReadKey();

}
}
}

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