Linq基础

1.什么是Linq

LINQ（Language Integrated Query）语言集成查询是一组用于c#和Visual Basic语言的扩展。它允许编写C#或者Visual Basic代码以查询数据库相同的方式操作内存数据。

2.Linq基础中用数据访问类的情况

 public class UsersData
    {
        DBDataContext con = new DBDataContext();
        public List<Users> SelectAll()
        {
            List<Users> ulist = new List<Users>();
            ulist = con.Users.ToList();
            return ulist;
        }
        public bool Insert(Users u)
        {
            try
            {
                con.Users.InsertOnSubmit(u);
                con.SubmitChanges();
                return true;
            }
            catch { }
            return false;
        }

3.Linq抛弃数据访问类与实体类的用法

 using (DBDataContext con = new DBDataContext())
            {
                string s = toolStripTextBox1.Text;
                //lambda表达式
                List<Users> ulist = con.Users.Where(hehe => hehe.NickName.Contains(s)).OrderByDescending(r => r.Ids).ToList();
                foreach (Users u in ulist)
                {    
                }
            }

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 if (listView1.SelectedItems.Count == 1)
            {
                using (DBDataContext con = new DBDataContext())
                {
                    List<Users> ulist = con.Users.Where(r => r.Ids.ToString() == listView1.SelectedItems[0].Text).ToList();

                    if (ulist.Count > 0)
                    {
                        con.Users.DeleteOnSubmit(ulist[0]);
                        con.SubmitChanges();
                        shuaxin();
                    }
                }
            }

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  using (DBDataContext con = new DBDataContext())
            {
                Users u = con.Users.Where(r => r.Ids.ToString() == IDS).FirstOrDefault();
                if (u != null)
                {
                    u.NickName = textBox3.Text;
                    u.Sex = Convert.ToBoolean(textBox4.Text);
                    u.Birthday = Convert.ToDateTime(textBox5.Text);
                    u.NationCode = textBox6.Text;
                    con.SubmitChanges();
                }
            }