EF增删改查基础

#region 1.0 新增 -void Add()
/// <summary>
/// 1.0 新增
/// </summary>
static void Add()
{
    //1.1创建实体对象
    User uObj = new User()
    {
        uName = "刘德华",
        uLoginName = "aaa",
        uPwd = "asdfasdfasdfsadf",
        uIsDel = false,
        uAddtime = DateTime.Now
    };
    //1.2通过EF新增到数据库
    //1.2.1将对象 加入到 数据上下文 的 User集合中
    db.Users.Add(uObj);
    //1.2.2调用数据上下文 的 保存方法，将 对象 存数数据库
    db.SaveChanges();
    Console.WriteLine("保存成功~~！");
}
#endregion

#region 2.0 简单查询 -void Query()
/// <summary>
/// 2.0 简单查询
/// </summary>
static void Query()
{
    List<User> list = db.Users.Where(u => u.uName == "刘德华").ToList();
    list.ForEach(u => Console.WriteLine(u.ToString()));
}
#endregion

#region 3.0 官方推荐的 修改方式（先查询，再修改）
/// <summary>
/// 3.0 官方推荐的 修改方式（先查询，再修改）
/// </summary>
static void Edit()
{
    //1.查询出一个 要修改的对象
    User usr = db.Users.Where(u => u.uId == 1).FirstOrDefault();
    Console.WriteLine("修改前：" + usr.ToString());
    //2.修改内容
    usr.uName = "刘德华";
    usr.uLoginName = "liudehua";
    //3.重新保存到数据库
    db.SaveChanges();
    Console.WriteLine("修改成功：");
    Console.WriteLine(usr.ToString());
}
#endregion

#region 4.0 删除 -void Delete()
/// <summary>
/// 4.0 删除
/// </summary>
static void Delete()
{
    //4.1创建要删除的 对象
    User u = new User() { uId = 6 };
    //4.2附加到 EF中，Remove前必须Attach
    db.Users.Attach(u);
    //4.3标记为删除
    db.Users.Remove(u);
    //4.4执行删除sql
    db.SaveChanges();
    Console.WriteLine("删除成功~~~");
}
#endregion

重写实体类ToString方法：

public partial class User
{
    public override string ToString()
    {
        return this.uId + "," + this.uName + "," + this.uLoginName + "," + this.uPwd;
    }
}

二、

//1.添加(增)
EFDBEntities entity = new EFDBEntities();
Users users = new Users() { username = "aaa", password = "111" };
entity.Entry(users).State = EntityState.Added;
entity.SaveChanges();
//2.删除(删)
EFDBEntities entity = new EFDBEntities();
Users users = new Users() { id = 4 };
entity.Entry(users).State = EntityState.Deleted;
entity.SaveChanges();
//3.修改(改)
EFDBEntities entity = new EFDBEntities();
Users users = new Users() { id = 4, username = "rrr", password = "333" };
entity.Entry(users).State = EntityState.Modified;
entity.SaveChanges();
//4.查询(查)
//获取所有数据
var list = entity.Users;
foreach (var item in list)
{
Console.WriteLine(item.id + "---" + item.username + "---" + item.password);
}
//第一种方法，查询id=1的数据
IQueryable<Users> list1 = from u in entity.Users
where u.id == 1
select u;
//第二种方法，查询id=1的数据    
IQueryable<Users> list2 = entity.Users.Where(i => i.id == 3);
//查询第一条数据
Users us = entity.Users.FirstOrDefault();
//遍历
foreach (var item in list1)
{
    Console.WriteLine(item.id + "---" + item.username + "---" + item.password);
}

总结：

static TextEntities db = new TextEntities();

1.添加：

Users user = new Users() { Id = 5, Name = "ppp", Pwd = "mmm", Gender = true, PowerId = 5 };

db.Users.Add(user); =======>这条语句等价于 db.Entry(user).State = EntityState.Added;

2.删除：

Users user = new Users() { Id = 5 };

db.Users.Attach(user);

db.Users.Remove(user);=======>这两条语句等价于 db.Entry(user).State = EntityState.Deleted;