EF 增删改

  一、新增

    UserInfo user = new UserInfo()
    {
        UserName = "jamsebing",
        UserPass = "123456"
    };
     db.UserInfo.Add(user);

  二、删除之 [Entry].State=Deleted

    var user = new UserInfo()
    {
        UserID = 1, //根据主键删除
        UserName="jamesbing"
    };
    db.Entry<UserInfo>(user).State = System.Data.Entity.EntityState.Deleted;

    这里指定了UserName没有任何意义，只需填写UserId即可

       删除之 [Attach+Remove]

  var user = new UserInfo()
    {
        UserID = 1 //根据主键删除
    };
    //Attach的实体事先不能已经在内存中,否则上下文会追踪到两个相同键名的实体
    //将对象添加到EF管理容器中 ObjectStateManager
    db.UserInfo.Attach(user);
    ////将对象包装类状态标识为删除
    db.UserInfo.Remove(user);

      删除之 [先查询实体 再删除]

       // 执行了2次sql 效率略低 ,一次查询，一次删除
        var user = (from u in db.UserInfo where u.UserID == 1 select u).FirstOrDefault();
        db.UserInfo.Remove(user);
        db.SaveChanges();

  三、修改整个实体  [Entry].State=Modified

 //手动创建整个修改实体
   var user = new UserInfo()
    {
        UserID = 1,
        UserName = "jamesbing2",
        UserPass = "654321"
    };
    db.Entry<UserInfo>(user).State = System.Data.Entity.EntityState.Modified;

          修改指定字段之 [Attach(entity)]

var user = new UserInfo()
    {
        UserID = 1,
        UserName = "jamesbing2"
    };
   //State默认值=System.Data.EntityState.Unchanged

   var entry=db.UserInfo.Attach(user);

    //设置需要修改的字段 
   entry.Property<string>(v => v.UserName).IsModified = true;

          修改指定字段之 [Entry(entity)].State=Unchanged

   var user = new UserInfo()
    {
        UserID = 1,
        UserName = "jamesbing2"
    };
   var entry= db.Entry<UserInfo>(user);
   //如果使用 Attach 就不需要这句
   entry.State = System.Data.EntityState.Unchanged;
   //设置需要修改的字段
   entry.Property<string>(v => v.UserName).IsModified = true;