LINQ的最简单的增删改查写法

Posted 2020-10-17 _Iniesta

 .ToList();//返回一个集合，包含查到的所有值；

.First();//返回查到的第一条数据，如果查不到会报错；

.FirstOrDefault();返回查到的第一条数据，差不到返回一个null；

db.Users.InsertOnSubmit();//添加

db.DeleteOrSubmit();//删除
db.SubmitChanges();//提交修改，增删改都需要提交；

//修改取到对象之后直接赋值，提交；

 

//基础查，把内容放到泛型集合
using(DBDataContext db = new DBDataContext())
{
   List<Users> ulist = db.Users.ToList();
}
//模糊差，contains包含
string a = "123";
using(DBDataContext db = new DBDataContext())
{
   List<Users> ulist = db.Users.where(r => r.Ids.Contains(a))ToList();
}
//精确查，
string a = "123";
using(DBDataContext db = new DBDataContext())
{
   List<Users> ulist = db.Users.where(r => r.Ids==a)ToList();
}
//添加
Users u = new Users();
u.ids = "1";
u.UserName = "2";
u.password = "3";
using(DBdataContext db = new DBDataTaxt())
{
try
{
    db.Users.InsertOnSubmit(u);
    db.SubmitChanges();
    MessageBox.Show("成功");
}
catch
{
    MessageBox.Show("失败");
}
}
//修改
string a = "1";
using(DBdataContext db = new DBDataTaxt())
{
try
{
    Users u = db.Usres.where(r => r.ids == a).FirstOrDefault();
    u.ids = "3";
    u.UserName = "2";
    u.password = "1";
    db.SubmitChanges();
    MessageBox.Show("成功");
}
catch
{
    MessageBox.Show("失败");
}
}

//删除
string a = "1";
using(DBdataContext db = new DBDataTaxt())
{
    List<Users> ulist = db.Users.where(r => r.Ids == a).ToList();
    if(ulist.Count > 0)
    {
        db.DeleteOnSubmit(ulist[0]);
        db.SubmitChanges();
    }
}