[英]Using Select and Where in a List using LINQ statement
這是MySQL
表。
+-------+-------+
| p_int | p_uni |
+-------+-------+
| 0 | seat |
| 1 | X400 |
| 4 | X400 |
| 2 | X400 |
| 2 | X4SVR |
| 3 | X400 |
+-------+-------+
6 rows in set
在使用Visual Studio 2019
、 C#
和.NET Framework 4.7
開發ASP.NET
的網站的MasterPage
中,我使用 MySQL 表的值創建了兩個List<string>
,如
List<string> Listp_uni = new List<string>();
List<string> Listp_int = new List<string>();
Container.p_int = reader["p_int"].ToString();
Container.p_uni = reader["p_uni"].ToString();
Listp_uni.Add(Container.p_uni.ToString());
Listp_int.Add(Container.p_int.ToString());
Container.p_uni = string.Join(",", Listp_uni.Select(e => "'" + e + "'").Distinct());
Container.p_int = string.Join(" ", Listp_int.Select(e => "" + e + "").Distinct());
這些List<string>
的返回是
'seat','X400','X4SVR'
0 1 4 2 3
我需要從選擇List<string> Listp_uni
值等於X4SVR
使用LINQ
我嘗試過但沒有成功
var studentNames = Mp.Container.p_uni.Where(s => s.Mp.Container.p_uni == "X4SVR")
.Select(s => s);
錯誤是
編譯器錯誤消息:CS1061:“char”不包含“Mp”的定義,並且找不到接受“char”類型的第一個參數的擴展方法“Mp”(您是否缺少 using 指令或程序集引用?)
我該怎么做?
編輯問題
public static class Container
{
public static string p_int
{
get
{
if (HttpContext.Current.Session["p_int"] != null)
{
return HttpContext.Current.Session["p_int"].ToString();
}
return null;
}
set
{
HttpContext.Current.Session["p_int"] = value;
}
}
public static string p_uni
{
get
{
if (HttpContext.Current.Session["p_uni"] != null)
{
return HttpContext.Current.Session["p_uni"].ToString();
}
return null;
}
set
{
HttpContext.Current.Session["p_uni"] = value;
}
}
}
string constr = ConfigurationManager.ConnectionStrings["cn"].ConnectionString;
using (MySqlConnection con =
new MySqlConnection(constr))
{
using (MySqlCommand cmd =
new MySqlCommand())
{
try
{
if (username != null)
{
con.Open();
cmd.Connection = con;
cmd.CommandText = "SP_ML_AUTE";
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.AddWithValue("tusername", username.ToString().ToUpper());
using (MySqlDataReader reader =
cmd.ExecuteReader())
{
if (reader.HasRows)
{
while (reader.Read())
{
Container.p_int = reader["p_int"].ToString();
Container.p_uni = reader["p_uni"].ToString();
Listp_uni.Add(Container.p_uni.ToString());
Listp_int.Add(Container.p_int.ToString());
}
Container.p_uni = string.Join(",", Listp_uni.Select(e => "'" + e + "'").Distinct());
Container.p_int = string.Join(" ", Listp_int.Select(e => "" + e + "").Distinct());
}
}
}
}
catch (Exception ex)
{
throw new ApplicationException("operation failed!", ex);
}
finally
{
cmd.Connection.Close();
}
}
}
新編輯
DataTable dt = new DataTable();
dt.Columns.Add("p_int", typeof(int));
dt.Columns.Add("p_uni", typeof(string));
dt.Rows.Add(new object[] { 0, "seat" });
dt.Rows.Add(new object[] { 1, "X400" });
dt.Rows.Add(new object[] { 4, "X400" });
dt.Rows.Add(new object[] { 2, "X400" });
dt.Rows.Add(new object[] { 2, "X4SVR" });
dt.Rows.Add(new object[] { 3, "X400" });
string p_int = string.Join(",", dt.AsEnumerable().Select(x => x.Field<int>("p_int")).Distinct());
string p_uni = string.Join(" ", dt.AsEnumerable().Select(z => z.Field<string>("p_uni")).Distinct());
Response.Write(p_int + "<br />" + p_uni + "<br /><br />");
var studentNames = p_uni.Where(s => s.p_uni == "X4SVR").Select(s => s);
Response.Write(studentNames);
首先,您必須了解我們不能在字符串中使用 select。 主要函數在鏈接中,請通過它字符串函數。 在下面的代碼中,我創建了一些用於選擇的示例
“X4SVR” 。 請檢查。 我的代碼不是更好的代碼。但它會給你一些解決問題的見解。
快樂編碼:)
DataTable dt = new DataTable();
dt.Columns.Add("p_int", typeof(int));
dt.Columns.Add("p_uni", typeof(string));
dt.Rows.Add(new object[] { 0, "seat" });
dt.Rows.Add(new object[] { 1, "X400" });
dt.Rows.Add(new object[] { 4, "X400" });
dt.Rows.Add(new object[] { 2, "X400" });
dt.Rows.Add(new object[] { 2, "X4SVR" });
dt.Rows.Add(new object[] { 3, "X400" });
string p_int = string.Join(",", dt.AsEnumerable().Select(x => x.Field<int>("p_int")).Distinct());
string p_uni = string.Join(" ", dt.AsEnumerable().Select(z => z.Field<string>("p_uni")).Distinct());
Response.Write(p_int + "<br />" + p_uni + "<br /><br />");
// if you want to get p_uni and p_int take from the datatable itself
//it will return matching p_uni and p_int
var studentNames = dt.AsEnumerable().Where(s => s.Field<string>("p_uni") == "X4SVR").Select(y => y);
//if you want get the name only
//Method - using the array
string [] p_uniArray = dt.AsEnumerable().Select(z => z.Field<string>("p_uni")).ToArray();
var studentNames1 = p_uniArray.AsEnumerable().Where(s => s == "X4SVR").Select(y => y);
//if you need to take from p_uni string it self please convert it into array like
//here you are not using any separator so I'm splitting it with space
var stName = p_uni.Split(" ");
var studentNames2 = stName.Where(x => x == "X4SVR").Select( y => y).Distinct();
// var studentNames = dt.Where(s => s.p_uni == "X4SVR").Select(s => s);
Response.Write(studentNames);
嘗試從數據表中執行以下操作:
DataTable dt = new DataTable();
dt.Columns.Add("p_int", typeof(int));
dt.Columns.Add("p_uni", typeof(string));
dt.Rows.Add(new object[] { 0, "seat"});
dt.Rows.Add(new object[] { 1, "X400"});
dt.Rows.Add(new object[] { 4, "X400"});
dt.Rows.Add(new object[] { 2, "X400"});
dt.Rows.Add(new object[] { 2, "X4SVR"});
dt.Rows.Add(new object[] { 3, "X400"});
string p_int = string.Join(",", dt.AsEnumerable().Select(e => e.Field<int>("p_int")).Distinct());
string p_uni = string.Join(" ", dt.AsEnumerable().Select(e => e.Field<string>("p_uni")).Distinct());
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