EF下lambda与linq查询&&扩展方法

1. linq查询数据

WebTestDBEntities db = new WebTestDBEntities();

1.1 linq查询所有列数据

var userInfoList = from u in db.UserInfo
where u.ID == 10
select u;

1.2 linq查询部分列数据

var userInfoList = from u in db.UserInfo
where u.ID >= 1
select new { Name = u.UserName, Pwd = u.UserPass };

foreach (var userInfo in userInfoList)
{
Response.Write(userInfo.Name + ":" + userInfo.Pwd + "<br/>");
}

2. lambda查询数据

2.1 lambda查询所有列数据

var userInfoList = db.UserInfo.Where<UserInfo>(u => u.ID > 0);
foreach (var userInfo in userInfoList)
{
Response.Write(userInfo.UserName + ":" + userInfo.UserPass + "<br/>");
}

2.2 lambda查询部分列数据

var userInfoList = db.UserInfo.Where<UserInfo>(u => u.ID > 0).Select(a => new { Name = a.UserName, Pwd = a.UserPass });
foreach (var userInfo in userInfoList)
{
Response.Write(userInfo.Name + ":" + userInfo.Pwd + "<br/>");
}

3. 排序

var userInfoList = db.UserInfo.Where<UserInfo>(c => true).OrderBy<UserInfo, int>(u => u.ID).Select(u => new { Name = u.UserName,Email=u.Email });//升序排序

var userInfoList = db.UserInfo.Where<UserInfo>(c => true).OrderByDescending<UserInfo, int>(u => u.ID).Select(u => new { Name = u.UserName, Email = u.Email });//降序排序

var userInfoList = (from u in db.UserInfo
select u).OrderByDescending<UserInfo, int>(c => c.ID).Select(u => new { Name = u.UserName, Email = u.Email });

4. 分页查询示例：

int pageIndex = 2;
int pageSize = 2;
var userInfoList = db.UserInfo.Where<UserInfo>(c => true).OrderBy<UserInfo, int>(u => u.ID).Skip<UserInfo>((pageIndex - 1) * pageSize).Take<UserInfo>(pageSize);
foreach (var userInfo in userInfoList)
{
Response.Write(userInfo.UserName + "<br/>");
}

5、扩展方法

static

this

public static string ShowMsg(this string ext, string msg)
{
return string.Format("<span style='color:red'>{0}</span>", msg);
}

string tempStr = string.Empty;
string resultStr = tempStr.ShowMsg("扩展方法示例");
Response.Write(resultStr);