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DataTable returns null WPF

I want to display data in a datagrid based on value selected in a ComboBox but my datatable function returns null and nothing is displayed in the datagrid.
public DataTable ReadData(User user)
{
using (SqlConnection db = new SqlConnection(AppConnect.Connection))
{
string query = "SELECT moduleCode,moduleName,modCredits,modHrsLeft FROM [Module] WHERE userName=#userName";
try
{
using (SqlCommand command = new SqlCommand(query, db))
{
if (db.State == ConnectionState.Closed)
{
db.Open();
command.Parameters.AddWithValue("#userName", user.UserName);
SqlDataAdapter dataAdapter = new SqlDataAdapter(command);
table = new DataTable();
dataAdapter.Fill(table);
}
}
db.Close();
}
catch (Exception e)
{
Console.WriteLine(e.Message);
}
return table;
}
}
This function is in a class library. The function is called in the WPF project, this is the code:
private void BtnDisplay_Click(object sender, RoutedEventArgs e)
{
string userName = CmboxUserN.SelectedItem.ToString();
User user1 = new User
{
UserName = userName
};
DataTable table = data.ReadData(user1);
gridModules.DataContext= table;
}

Try these changes. It seems that the line table = new DataTable(); is never being hit. You don't need to check to make sure the connection is in a closed state because you are using a using statement.
public DataTable ReadData(User user)
{
using (SqlConnection db = new SqlConnection(AppConnect.Connection))
{
string query = "SELECT moduleCode,moduleName,modCredits,modHrsLeft FROM [Module] WHERE userName=#userName";
try
{
using (SqlCommand command = new SqlCommand(query, db))
{
db.Open();
command.Parameters.AddWithValue("#userName", user.UserName);
SqlDataAdapter dataAdapter = new SqlDataAdapter(command);
table = new DataTable();
dataAdapter.Fill(table);
}
}
catch (Exception e)
{
Console.WriteLine(e.Message);
}
return table;
}
}
Also, you don't need to .Close() the connection because the SqlConnection is in a using statement, which means the object will be disposed of when the scope of the using statement is exited.
One other tip: You should change the code to have the try catch around everyting and if there are any errors at all, log the errors to console and return a new DataTable().

DataTable returns "0" as value

I have a problem with getting data from sqlite database. Normally it works fine in other forms but on my last query all the returns "0".
try
{
using (SQLiteConnection baglanti = new SQLiteConnection(Uygulama.baglantiMetni))
{
if (baglanti.State != ConnectionState.Open)
baglanti.Open();
string sorgu = "SELECT tyOzellikDegerID, tyOzellikDegeri FROM tblTYKategoriOzellikDegerleri WHERE tyOzellikID=:ozellikkodu";
using (SQLiteDataAdapter da = new SQLiteDataAdapter(sorgu, baglanti))
{
da.SelectCommand.Parameters.AddWithValue(":ozellikkodu", Convert.ToInt32(kod));
DataTable dt = new DataTable();
da.Fill(dt);
cmbTYOzellikDegerleri.DisplayMember = "tyOzellikDegeri";
cmbTYOzellikDegerleri.ValueMember = "tyOzellikDegerID";
cmbTYOzellikDegerleri.DataSource = dt;
foreach(DataRow dr in dt.Rows)
{
Console.WriteLine(dr["tyOzellikDegeri"].ToString());
}
}
}
}
catch (Exception hata)
{
if (Uygulama.logTut == 1)
Fonksiyonlar.logYaz("FrmTeyStokListesi - ggOzellikDegeleri(" + kod + ") - " + hata.Message);
}
DataRow returns "0".
But if I run the code on sqlitedatabrowser it works fine.
I couldn't find the problem.

SqlHelper DataAdapter

I am using a SqlHelper class which has common methods for CRUD operations.
public static void Fill(DataSet dataSet, String procedureName)
{
SqlConnection oConnection = new SqlConnection(DBInterface.ConnectionString);
SqlCommand oCommand = new SqlCommand(procedureName, oConnection);
oCommand.CommandType = CommandType.StoredProcedure;
SqlDataAdapter oAdapter = new SqlDataAdapter();
oAdapter.SelectCommand = oCommand;
oConnection.Open();
using (SqlTransaction oTransaction = oConnection.BeginTransaction())
{
try
{
oAdapter.SelectCommand.Transaction = oTransaction;
oAdapter.Fill(dataSet);
oTransaction.Commit();
}
catch
{
oTransaction.Rollback();
throw;
}
finally
{
if (oConnection.State == ConnectionState.Open)
oConnection.Close();
oConnection.Dispose();
oAdapter.Dispose();
}
}
}
Now in my code, I am calling this method as,
private void BindCustomers()
{
DataSet dsCust = new DataSet();
SqlHelper.Fill(dsCust, "getCustomers");
--then I bind this dataset to datagridview
}
This all works fine. Now I want to update the data in the database. But I am confused how do I call DataAdatpaer.Update(dataset) here to update the changes made in datagridview into database. Is this possible here? Or I need to do it conventionally to find the updated row and call the ExecuteNonQuery function in the SqlHelper? Is there anything which can be done to use dataadapter.update(ds)
Thanks

You don't need to hide data adapter, or if for any reason you did so, you need to expose a method in your class to push updates to server.
Example
Public class SqlHelper
{
string commandText;
string connectionString;
public SqlHelper(string command, string connection)
{
commandText = command;
connectionString = connection;
}
public DataTable Select()
{
var table = new DataTable();
using (var adapter = new SqlDataAdapter(this.commandText, this.connectionString))
adapter.Fill(table)
return table;
}
public void Update(DataTable table)
{
using (var adapter = new SqlDataAdapter(this.commandText, this.connectionString))
{
var builder = new SqlCommandBuilder(adapter);
adapter.Update(table);
}
}
}

By calling this method in your code you can perform all crud operation select, update, delete and insert. you just need to pass connection string, procedure name and parameters list. Using this method you will retrieve data in the DataTable.if anyone want Dataset(Multiple Result) then just need to replace DataSet on the place of DataTable
SqlConnection conn = new SqlConnection("Your ConnectionString");
public DataTable ExecuteDataTable(string ProcedureName, SqlParameter[] _Param)
{
try
{
DataTable dataTable = new DataTable();
SqlCommand cmd = new SqlCommand(ProcedureName, conn);
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.Clear();
if (_Param is not null)
{
for (int i = 0; i < _Param.Length; i++)
{
if (_Param[i].ParameterName is not null)
{
if (_Param[i].Value is not null)
{
cmd.Parameters.AddWithValue(_Param[i].ParameterName, _Param[i].Value);
}
else
{
cmd.Parameters.AddWithValue(_Param[i].ParameterName, DBNull.Value);
}
}
}
}
conn.Open();
SqlDataAdapter DA = new SqlDataAdapter(cmd);
DA.Fill(dataTable);
conn.Close();
return dataTable;
}
catch (Exception ex)
{
conn.Close();
throw;
}
}

Not getting any row data from database using c# asp.net.

I can not get any row data from database using c# asp.net.I am trying to fetch one row data from my DB but it is not returning any row.I am using 3-tire architecture for this and i am explaining my code below.
index.aspx.cs:
protected void userLogin_Click(object sender, EventArgs e)
{
if (loginemail.Text.Trim().Length > 0 && loginpass.Text.Trim().Length >= 6)
{
objUserBO.email_id = loginemail.Text.Trim();
objUserBO.password = loginpass.Text.Trim();
DataTable dt= objUserBL.getUserDetails(objUserBO);
Response.Write(dt.Rows.Count);
}
}
userBL.cs:
public DataTable getUserDetails(userBO objUserBO)
{
userDL objUserDL = new userDL();
try
{
DataTable dt = objUserDL.getUserDetails(objUserBO);
return dt;
}
catch (Exception e)
{
throw e;
}
}
userDL.cs:
public DataTable getUserDetails(userBO objUserBO)
{
SqlConnection con = new SqlConnection(CmVar.convar);
try
{
con.Open();
DataTable dt = new DataTable();
string sql = "SELECT * from T_User_Master WHERE User_Email_ID= ' " + objUserBO.email_id + "'";
SqlCommand cmd = new SqlCommand(sql, con);
SqlDataAdapter objadp = new SqlDataAdapter(cmd);
objadp.Fill(dt);
con.Close();
return dt;
}
catch(Exception e)
{
throw e;
}
}
When i am checking the output of Response.Write(dt.Rows.Count);,it is showing 0.So please help me to resolve this issue.

It looks like your your query string has a redundant space between ' and " mark. That might be causing all the trouble as your email gets space in front.
It is by all means better to add parameters to your query with use of SqlConnection.Parameters property.
string sql = "SELECT * from T_User_Master WHERE User_Email_ID=#userID";
SqlCommand cmd = new SqlCommand(sql, con);
cmd.Parameters.Add("#userID", SqlDbType.NVarChar);
cmd.Parameters["#userID"].Value = objUserBO.email_id;

How to call a stored procedure using ADO.NET?

private void button1_Click(object sender, EventArgs e)
{
try
{
SqlConnection conn = new SqlConnection();
conn.ConnectionString = "Data Source=*******;Initial Catalog=ChatApp;User ID=Chatapplication;Password=****";
conn.Open();
SqlCommand cmd = new SqlCommand();
string chatroomidno = textBox1.Text;
string chatroomname = textBox2.Text;
//cmd.CommandText = "Select ChatRoomID=#ChatRoomID,ChatRoomName=#ChatRoomName from tblChatRoom";
//cmd.Connection = conn;
SqlDataAdapter adapt = new SqlDataAdapter("Chatroomapp",conn);
adapt.SelectCommand.CommandType = CommandType.StoredProcedure;
DataSet ds=new DataSet();
DataTable dt = new DataTable();
adapt.SelectCommand.Parameters.Add(new SqlParameter("#ChatRoomID", SqlDbType.VarChar, 100));
adapt.SelectCommand.Parameters["#ChatRoomID"].Value = chatroomidno;
adapt.SelectCommand.Parameters.Add(new SqlParameter("#ChatRoomName", SqlDbType.VarChar, 50));
adapt.SelectCommand.Parameters["#ChatRoomName"].Value = chatroomname;
adapt.Fill(ds, "tblChatRoom");
if (dt.Rows.Count > 0)
{
MessageBox.Show("Connection Succedded");
}
else
{
MessageBox.Show("Connection Fails");
}
}
catch (Exception ex)
{
MessageBox.Show("Error", ex.Message);
}
}
While compiling the program I got only connection fails message box, in the database. I found correct, how to overcome the program to get the connection succeeded message box.

Well, you're filling the ds data set - but then you're checking the dt data table for presence of rows... that's never going to work, of course!
If you only need a single DataTable - just use and fill that data table alone - no need for the overhead of a DataSet. Also, put your SqlConnection and SqlCommand into using blocks like this:
using (SqlConnection conn = new SqlConnection("Data Source=*******;Initial Catalog=ChatApp;User ID=Chatapplication;Password=****"))
using (SqlCommand cmd = new SqlCommand("Chatroomapp", conn))
{
string chatroomidno = textBox1.Text;
string chatroomname = textBox2.Text;
SqlDataAdapter adapt = new SqlDataAdapter(cmd);
adapt.SelectCommand.CommandType = CommandType.StoredProcedure;
adapt.SelectCommand.Parameters.Add(new SqlParameter("#ChatRoomID", SqlDbType.VarChar, 100));
adapt.SelectCommand.Parameters["#ChatRoomID"].Value = chatroomidno;
adapt.SelectCommand.Parameters.Add(new SqlParameter("#ChatRoomName", SqlDbType.VarChar, 50));
adapt.SelectCommand.Parameters["#ChatRoomName"].Value = chatroomname;
// fill the data table - no need to explicitly call `conn.Open()` -
// the SqlDataAdapter automatically does this (and closes the connection, too)
DataTable dt = new DataTable();
adapt.Fill(dt);
if (dt.Rows.Count > 0)
{
MessageBox.Show("Connection Succedded");
}
else
{
MessageBox.Show("Connection Fails");
}
}
And just because you get back no rows in dt.Rows doesn't necessarily mean that your connection failed..... it could just be that there are no rows that match your search critieria! The connection worked just fine - but the SQL command just didn't return any rows.

Connection failed means that something went wrong between your program and the database. No records returned does not mean that the connection failed. It just means that your table is empty - it contains no records.
Using ADO.NET and a stored procedures would have been a little different from what you have done it. If you need to check if the connection failed, maybe it is better to check the type of exception that is returned in the catch part.
Below is how I would have done it. I would have created a separate method that would have handled my call, and then in your button1_Click I would have just called this method:
public async Task<ChatRoom> GetAsync(string chatRoomId, string chatRoomName)
{
try
{
string connectionString = ConfigurationManager.ConnectionStrings["Db"].ConnectionString;
using (SqlConnection sqlConnection = new SqlConnection(connectionString))
{
await sqlConnection.OpenAsync();
using (SqlCommand sqlCommand = new SqlCommand("ChatRooms_Get", sqlConnection))
{
sqlCommand.CommandType = CommandType.StoredProcedure;
sqlCommand.Parameters.Add(new SqlParameter("#ChatRoomID", chatRoomId));
sqlCommand.Parameters.Add(new SqlParameter("#ChatRoomName", chatRoomName));
using (SqlDataReader sqlDataReader = await sqlCommand.ExecuteReaderAsync())
{
ChatRoom chatRoom = null;
if (await sqlDataReader.ReadAsync())
{
chatRoom = new ChatRoom();
chatRoom.Id = sqlDataReader.GetFieldValue<string>(0);
chatRoom.Name = sqlDataReader.GetFieldValue<string>(1);
chatRooms.Add(chatRoom);
}
return chatRoom;
}
}
}
}
catch (Exception exception)
{
// Try checking if the connection failed here
throw exception;
}
}
My chat room domain model could have looked like this:
public class ChatRoom
{
public string Id { get; set; }
public string Name { get; set; }
}
And the stored procedure would have looked like this:
CREATE PROCEDURE [dbo].[ChatRooms_Get]
(
#ChatRoomID VARCHAR(100),
#ChatRoomName VARCHAR(50)
)
AS
BEGIN
SET NOCOUNT ON;
SELECT
ChatRoomID,
ChatRoomName
FROM
tblChatRoom
WHERE
ChatRoomID = #ChatRoomID
AND ChatRoomName = #ChatRoomName;
END
GO
And then in the calling method you would get the chatroom and do with it whatever you need to do with it. For this example I just checked if it exists or not:
try
{
ChatRoom chatRoom = await chatRoomRepository.GetAsync(chatRoomId, chatRoomName);
if (chatRoom != null)
{
MessageBox.Show("Record found");
}
else
{
MessageBox.Show("No record found");
}
}
catch (Exception exception)
{
throw exception;
}
I hope this can help.