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How to sort a dataset in ASP.NET C#

I am trying to sort a datatable into a DataSet. I want to sort by the Status Column in "DESC". But I am not aware how to go about this. I have tried the suggested solutions online but I seem not to be doing something right. Here is what I have tried, albeit, I have commented out the sorting lines of the code as they do not work for me. How can I sort my table using the Status column in Desc?
[WebMethod(EnableSession = true)]
public List < TaskListClass > getTasks() {
var userId = Session["UserId"].ToString();
List < TaskListClass > objB = new List < TaskListClass > ();
try {
using(var connection = new SqlConnection(ConfigurationManager.ConnectionStrings["DBConnString"].ToString())) {
connection.Open();
DataSet Myds = new DataSet();
// Myds.Tables[0].DefaultView.Sort = "Status desc";
SqlDataAdapter sqldr = new SqlDataAdapter();
string ProcName = "getTasks";
SqlCommand cmd = new SqlCommand(ProcName, connection);
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.Add("#userId", SqlDbType.VarChar, 900).Value = userId;
sqldr.SelectCommand = cmd;
sqldr.Fill(Myds);
DataTable dt = Myds.Tables[0];
// DataTable dt = Myds.Tables[0].DefaultView.ToTable();
for (int i = 0; i < dt.Rows.Count; i++) {
objB.Add(new TaskListClass() {
Id = Convert.ToString(dt.Rows[i]["Id"]),
Subject = Convert.ToString(dt.Rows[i]["Subject"]),
Customer = Convert.ToString(dt.Rows[i]["Customer"]),
Sender = Convert.ToString(dt.Rows[i]["Sender"]),
Receiver = Convert.ToString(dt.Rows[i]["Receiver"]),
Priority = Convert.ToString(dt.Rows[i]["Priority"]),
StartDate = Convert.ToString(dt.Rows[i]["StartDate"]),
EndDate = Convert.ToString(dt.Rows[i]["EndDate"]),
Status = Convert.ToString(dt.Rows[i]["Status"]),
OnProgress = Convert.ToString(dt.Rows[i]["OnProgress"]),
});
}
}
} catch (Exception e) {
msg = e.ToString();
}
return objB;
}

Ok, a few things.
first up, a dataset is a collection of tables - "many tables" possible.
But you have ONE table, so why use a dataset? I see no need. Just use a single data table for this.
And this will reduce the code.
So, I suggest this, or close to this:
using (var connection = new SqlConnection(ConfigurationManager.ConnectionStrings["DBConnString"].ToString()))
{
using (var cmd = new SqlCommand("getTasks", connection))
{
connection.Open();
cmd.CommandType = CommandType.StoredProcedure;
DataTable dt = new DataTable();
cmd.Parameters.Add("#userId", SqlDbType.VarChar).Value = userId;
dt.Load(cmd.ExecuteReader());
// now sort the datatable
dt.DefaultView.Sort = "Status DESC";
// now fill out our object with each row
foreach (DataRow OneRow in dt.Rows)
{
objB.Add(new TaskListClass()
{
Id = OneRow["Id"].ToString(),
Subject = OneRow["Subject"].ToString(),
Customer = OneRow["Customer"].ToString(),
Sender = OneRow["Sender"].ToString(),
Receiver = OneRow["Receiver"].ToString(),
Priority = OneRow["Priority"].ToString(),
StartDate = OneRow["StartDate"].ToString(),
EndDate = OneRow["EndDate"].ToString(),
Status = OneRow["Status"].ToString(),
OnProgress = OneRow["OnProgress"].ToString(),
}); ;
}
}
}
}
return objB;

The way the current code is written, you could add this after the for-loop:
objB = objB.OrderByDescending(t => t.Status).ToList();
Depending of the datatype of Status, it might be sorted alphabetically.

var dataRow = dt.AsEnumerable().OrderByDescending(x => x.Field<string>("Status")).ToList();
foreach (var item in dataRow)
{
//Enter your Code Here
}
Here dt is your datatable.
dataRow is a set of list.
After get the data list, you can asign it to your "objB".

DataTable Rows Count Null Exception

Im trying to fill a listview with data from my database but get a null reference exception when i load the listview. Im using MVC pattern.
Code in my data acces layer:
public List<Menu_Item> DB_Get_All_MenuItems()
{
string query = "SELECT * FROM [Menu_Items]";
SqlParameter[] sqlParameters = new SqlParameter[0];
return ReadTables(ExecuteSelectQuery(query, sqlParameters));
}
private List<Menu_Item> ReadTables(DataTable dataTable)
{
List<Menu_Item> menu_items = new List<Menu_Item>();
foreach (DataRow dr in dataTable.Rows)
{
Menu_Item menu_Item = new Menu_Item()
{
Menu_ID = (int)dr["Menu_ID"],
Naam = (string)dr["Naam"],
Prijs = (float)dr["Prijs"],
Voorraad = (int)dr["Voorraad"],
Categorie_ID = (int)dr["Catogorie_ID"]
};
menu_items.Add(menu_Item);
}
return menu_items;
}
I have checked and my SQL parameters are all spelled correctly
The exact error is: datatable.rows = 'datatable.rows' threw an exception of type 'system.nullreferenceexception'
My DateTable method looks like this
protected DataTable ExecuteSelectQuery(string query, params SqlParameter[] sqlParameters)
{
SqlCommand command = new SqlCommand();
DataTable dataTable;
DataSet dataSet = new DataSet();
try
{
command.Connection = OpenConnection();
command.CommandText = query;
command.Parameters.AddRange(sqlParameters);
command.ExecuteNonQuery();
adapter.SelectCommand = command;
adapter.Fill(dataSet);
dataTable = dataSet.Tables[0];
}
catch (SqlException e)
{
return null;
throw new Exception(e.ToString());
}
finally
{
CloseConnection();
}
return dataTable;
}

Check whether dataTable null or not
if(dataTable!=null && dataTable.Rows.Count > 0)
{
foreach (DataRow dr in dataTable.Rows)
{
Menu_Item menu_Item = new Menu_Item()
{
Menu_ID = (int)dr["Menu_ID"],
Naam = (string)dr["Naam"],
Prijs = (float)dr["Prijs"],
Voorraad = (int)dr["Voorraad"],
Categorie_ID = (int)dr["Catogorie_ID"]
};
menu_items.Add(menu_Item);
}
}

check if the datarows.count is null or not ...
Also in DB_Get_All_MenuItems() mention dbconnction string, sql command type, and datareader and all...first make sure the datas is returning in this function o/p....

You are trying to use something that is null. This means you either set it to null, or you never set it to anything at all.
Now, You can then place a breakpoint at every found location and run your program with the debugger attached. Every time the debugger breaks on such a breakpoint, you need to determine whether you expect the reference to be non-null.

Binding ComboBox to DataTable (WinForms c#)?

I have a method which populates my ComboBox from a DataTable:
public string populateCompanyTransSellingEntityLookUp(ref System.Windows.Forms.ComboBox Combo, string Id, Contract Contract)
{
SqlCommand _comm = new SqlCommand();
_comm.Parameters.AddWithValue("#id", Id);
_comm.CommandText = "SELECT [name] FROM dbo.fnGetList(#id) ORDER BY [name]; ";
_comm.Connection = _conn;
_comm.CommandTimeout = _command_timeout;
DataTable dt = new DataTable();
try
{
SqlDataReader myReader = _comm.ExecuteReader();
dt.Load(myReader);
Combo.DataSource = dt;
Combo.DisplayMember = "name";
foreach (DataRow dr in dt.Rows)
{
if (dr["name"].ToString() == Contract.Company_Name.ToString())
{
Combo.Text = dr["company_int_name"].ToString();
}
}
}
catch
{
MessageBox.Show("Unable to populate Company Name LookUp");
}
return "";
}
I'm passing my saved value Contract.Company_Name into the forEach loop to find my required SelectedItem from the DataTable. The ComboBox is populated with my DataTable values from Combo.Datasource =dt; but my selected item isn't being set. The code compiles without exception. If I remove Datasource = dt;, theSelectedItemis set no problem. Why is theDatasourceoverriding mySelectedItem` and is there something I've missed with my binding?
Thanks all

At first you have to set the valueMember for sure. Then you can set the selectedValue Property instead of SelectedItem. The Item is one datasource record. So in your case it would be SelectedItem = dr! But iam not sure this is working.

Try this:
Combo.SelectedItem = dr;

I would suggest to use SelectedValue, then you don't need to loop through values "manually".
Also you don't need to use "heavy-weight" DataTable where you need just a collection of string values.
private IEnumerable<string> LoadNames(string id)
{
var query = "SELECT [name] FROM dbo.fnGetList(#id) ORDER BY [name]";
using (var connection = new SqlConnection("connectionString")
using (var command = new SqlCommand(query, connection)
{
// 36 is the size of the VarChar column in database(use your value)
command.Parameters.Add("#id", SqlDbType.VarChar, 36).Value = id;
connection.Open();
using (var reader = command.ExecuteReader())
{
var names = new List<string>();
while(reader.Read())
{
names.Add(reader.GetString(0));
}
return names;
}
}
}
public void Populate(ComboBox combobox, string id, Contract contract)
{
combobox.DataSource = LoadNames(id);
combobox.SelectedValue = contract.Copmpany_Name.ToString();
}
Few things to notice:
Dispose all objects which dealing with external resources (SqlConnection, SqlCommand and SqlDataReader)
Create SqlParameter with precise information about the type, for strings is important to provide size of the column in database. This information will improve SQL query performance on server side.
Don't pass combobox as a reference, populate method does not create new instance but only consume the given ComboBox instance.

Thank you for the help, I edited the code given that my problem was much more trivial.
public string populate_comboBox(ref System.Windows.Forms.ComboBox Combo)
{
SqlCommand _comm = new SqlCommand();
//edited for a simple one column sql query
_comm.CommandText ="SELECT [Column] FROM dbo.SQL_Table ORDER BY [Column];";
//MUST open sql connection to DB
SqlConnection conn = new SqlConnection(global_DB_String_Connection);
conn.Open();
_comm.Connection = conn;
DataTable dt = new DataTable();
try
{
SqlDataReader myReader = _comm.ExecuteReader();
dt.Load(myReader);
Combo.DataSource = dt;
Combo.DisplayMember = "ColumnName";
foreach (DataRow dr in dt.Rows)
{
//populates the combo box with query results
Combo.Text = dr["ColumnName"].ToString();
}
}
catch
{
Console.WriteLine("ComboBox Populate method has failed! ");
}
conn.Close();
return "";
}

store select result

i want to extract my table names and save it into variables this is my cod that return 3 answer:student, teacher and score. how can i change it to save these tree table name to 3 variable. thank you.
try
{
SqlDataReader myreader = null;
SqlCommand mycommand = new SqlCommand("select * FROM information_schema.tables WHERE table_type = 'BASE TABLE'", myconnect);
myreader = mycommand.ExecuteReader();
while (myreader.Read())
{
Console.WriteLine(myreader[2].ToString());
}
}

A simple builtin way is using Connection.GetSchema:
using (var con = new System.Data.SqlClient.SqlConnection(conStr))
{
con.Open();
DataTable schemaTable = con.GetSchema("Tables");
IList<string> allTableNames = schemaTable.AsEnumerable()
.Where(r => r.Field<string>("TABLE_TYPE") == "BASE TABLE")
.Select(r => r.Field<string>("TABLE_NAME"))
.ToList();
}
Now you have a List<string> with all table names which you can access via indexer or in a loop or create a comma separated list with string.Join:
string tNames = string.Join(",", allTableNames);
Console.Write("all tables in the given database: " + tNames);

You can use this :
string tableName ="" ; // Variable to stroe the table names
string connectionString = ""; //Your connectionstring
// get records from the table
string commandString =""; //Your query
// create the data set command object
// and the DataSet
SqlDataAdapter DataAdapter =new SqlDataAdapter(commandString, connectionString);
DataSet DataSet = new DataSet( );
// fill the DataSet object
DataAdapter.Fill(DataSet, "Customers");
// Get the one table from the DataSet
DataTable dataTable = DataSet.Tables[0];
// for each row in the table, display the info
foreach (DataRow dataRow in dataTable.Rows)
{
tableName = dataRow[0].tostring();
//...
}

if you want to save the result for future user or a different session then you can use any of the following to methods
first one
use the "insert" query to save the result one by one in the a different table that you would create specially for saving the data
you can put the insert command/statement directly into the for loop
second method
use the xml to store the value very simple and memory friendly

I Have modified #Doctor code to use ArrayList to store number of table name in single variables.
ArrayList alTableName = new ArrayList(); // Variable to stroe the table names
string connectionString = ""; //Your connectionstring
// get records from the table
string commandString =""; //Your query
// create the data set command object
// and the DataSet
SqlDataAdapter DataAdapter =new SqlDataAdapter(commandString, connectionString);
DataSet DataSet = new DataSet( );
// fill the DataSet object
DataAdapter.Fill(DataSet, "Customers");
// Get the one table from the DataSet
DataTable dataTable = DataSet.Tables[0];
// for each row in the table, display the info
foreach (DataRow dataRow in dataTable.Rows)
{
alTableName.Add(dataRow[0].tostring());
//...
}

How to iterate through a DataTable

I need to iterate through a DataTable. I have an column there named ImagePath.
When I am using DataReader I do it this way:
SqlDataReader dr = null;
dr = cmd.ExecuteReader();
while (dr.Read())
{
TextBox1.Text = dr["ImagePath"].ToString();
}
How can I achieve the same thing using DataTable?

DataTable dt = new DataTable();
SqlDataAdapter adapter = new SqlDataAdapter(cmd);
adapter.Fill(dt);
foreach(DataRow row in dt.Rows)
{
TextBox1.Text = row["ImagePath"].ToString();
}
...assumes the connection is open and the command is set up properly. I also didn't check the syntax, but it should give you the idea.

foreach (DataRow row in myDataTable.Rows)
{
Console.WriteLine(row["ImagePath"]);
}
I am writing this from memory.
Hope this gives you enough hint to understand the object model.
DataTable -> DataRowCollection -> DataRow (which one can use & look for column contents for that row, either using columnName or ordinal).
-> = contains.

You can also use linq extensions for DataSets:
var imagePaths = dt.AsEnumerble().Select(r => r.Field<string>("ImagePath");
foreach(string imgPath in imagePaths)
{
TextBox1.Text = imgPath;
}

There are already nice solution has been given. The below code can help others to query over datatable and get the value of each row of the datatable for the ImagePath column.
for (int i = 0; i < dataTable.Rows.Count; i++)
{
var theUrl = dataTable.Rows[i]["ImagePath"].ToString();
}

The above examples are quite helpful. But, if we want to check if a particular row is having a particular value or not. If yes then delete and break and in case of no value found straight throw error. Below code works:
foreach (DataRow row in dtData.Rows)
{
if (row["Column_name"].ToString() == txtBox.Text)
{
// Getting the sequence number from the textbox.
string strName1 = txtRowDeletion.Text;
// Creating the SqlCommand object to access the stored procedure
// used to get the data for the grid.
string strDeleteData = "Sp_name";
SqlCommand cmdDeleteData = new SqlCommand(strDeleteData, conn);
cmdDeleteData.CommandType = System.Data.CommandType.StoredProcedure;
// Running the query.
conn.Open();
cmdDeleteData.ExecuteNonQuery();
conn.Close();
GetData();
dtData = (DataTable)Session["GetData"];
BindGrid(dtData);
lblMsgForDeletion.Text = "The row successfully deleted !!" + txtRowDeletion.Text;
txtRowDeletion.Text = "";
break;
}
else
{
lblMsgForDeletion.Text = "The row is not present ";
}
}

foreach(DataGridViewRow row in dataGridView1){ var a = row.Cells[4].Value.ToString(); }