Develop Reference

Why Datatables return Null when it is executed via SQL Command text?

I got two classes, one for db connection and another to get data. When I use the SqlCommand type as stored procedure it returns the data table properly, but when I change the command type to text and change the command text properly it returns a null value. Why is this happening?
Class 1
public class DB_Connection
{
public SqlConnection cnn;
public SqlCommand cmd;
public SqlDataAdapter ada;
public DB_Connection()
{
cnn = new SqlConnection("Data Source=svr01;Initial Catalog=PDFScramble;Integrated Security=True");
cnn.Open();
cmd = new SqlCommand();
cmd.CommandType = CommandType.Text;// *changed in here SP or Text*
cmd.Connection = cnn;
ada = new SqlDataAdapter();
ada.SelectCommand = cmd;
}
Class 2
public class Data : DB_Connection
{
public string DException { get; set; }
public DataTable Datatable { get; set; }
public bool GetCivicEntities()
{
try
{
cmd.CommandText = "SELECT Id, Description, StateId ,EntityTypeId FROM CivicEntities";
ada.Fill(Datatable);// *Null in here*
return true;
}
catch (Exception ex)
{
DException = ex.Message;
return false;
}
}

Your Datatable is null, because of that you have this problem. This should fix it.
cmd.CommandText = "SELECT Id, Description, StateId ,EntityTypeId FROM CivicEntities";
Datatable = new DataTable();
ada.Fill(Datatable);
return true;

There is something wrong with the class structure. Check with this
using (SqlConnection conn = new SqlConnection("connectionString"))
{
SqlCommand cmd = null;
SqlParameter prm = null;
SqlDataAdapter dad = null;
DataTable dt = new DataTable();
cmd = new SqlCommand("SPName", conn);
cmd.CommandType = CommandType.StoredProcedure;
conn.Open();
dad = new SqlDataAdapter(cmd);
dad.Fill(dt);
conn.Close();
}
using (SqlConnection conn = new SqlConnection("connectionString"))
{
SqlCommand cmd = null;
SqlParameter prm = null;
SqlDataAdapter dad = null;
DataTable dt = new DataTable();
cmd = new SqlCommand("select * from dummy",conn);
cmd.CommandType = CommandType.StoredProcedure;
conn.Open();
dad = new SqlDataAdapter(cmd);
dad.Fill(dt);
conn.Close();
}

Load two / several MS Access Table into C# Windows Form

I´m asking how to connect two or more tables from an MS Access table into c# Windows forms?.
I get the error, that ue cant find the second table:
public partial class Form1 : Form
{
private OleDbConnection connection = new OleDbConnection();
private OleDbConnection connection2 = new OleDbConnection();
public Form1()
{
connection.ConnectionString = #"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Users\be\Documents\MitarbeiterDaten2.accdb;
Persist Security Info=False;";
connection2.ConnectionString = #"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Users\be\Documents\DatenbankAbteilung.accdb;
Persist Security Info=False;";
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
try
{
connection.Open();
OleDbCommand command = new OleDbCommand();
command.Connection = connection;
string query = "select ABTEILUNG from combo";
command.CommandText = query;
OleDbDataReader reader = command.ExecuteReader();
while (reader.Read())
{
Abteilung.Items.Add(reader["ABTEILUNG"].ToString());
}
connection.Close();
}
catch (Exception ex)
{
MessageBox.Show("Error" + ex);
}
finally
{
connection.Close();
}
Anybody got an solution?
Its just about, how to connect two or more MS Access tables into C# Windows forms.

You can reuse the the objects, and can get data from various tables or databases, as :
private void Form1_Load(object sender, EventArgs e)
{
try
{
connection.Open();
OleDbCommand command = new OleDbCommand();
command.Connection = connection;
string query = "select ABTEILUNG from combo";
command.CommandText = query;
OleDbDataReader reader = command.ExecuteReader();
while (reader.Read())
{
Abteilung.Items.Add(reader("ABTEILUNG").ToString());
}
reader.Close(); //' Always Close ther Reader. Don't left it open
connection2.Open();
command.Connection = connection2; //' Reusing Same Command Over New Connection
command.CommandText = "Select Field2 from Table2";
while (reader.Read)
{
if (!(Convert.IsDBNull(reader("Field2")))) //' Checking If Null Value is there
{
Abteilung.Items.Add(reader("Field2").ToString());
}
}
reader.Close();
}
catch (Exception ex)
{
MessageBox.Show("Error" + ex);
}
finally
{
connection.Close();
connection2.Close();
}
}

How about using using blocks to take care of the commands and connections and then using DataAdapter to get the job done easily. I use some code like this.
DataSet ds = new DataSet();
using (OleDbConnection con = new OleDbConnection(MDBConnection.ConnectionString))
{
con.Open();
using (OleDbCommand cmd = new OleDbCommand("SELECT Column FROM Table1", con))
{
using (OleDbDataAdapter da = new OleDbDataAdapter(cmd))
{
da.Fill(ds);
}
}
using (OleDbCommand cmd = new OleDbCommand("SELECT AnotherColumn FROM Table2", con))
{
using (OleDbDataAdapter da = new OleDbDataAdapter(cmd))
{
da.Fill(ds);
}
}
}
return ds;

Set datatables to be equivalent

This is probably a simple question but I am not experienced in C#.
I have 2 datatables, 1 is basically a copy of the other (like a table to review information). To set the values this is what I am doing now:
string attribute1 = "";
string attribute2 = "";
string attribute3 = "";
.....
DataTable result = new DataTable();
using (SqlConnection con = new SqlConnection("user id=user_id;password=pwd;server=serverstring;Trusted_Connection=yes;database=database;connection timeout=30"))
{
using (SqlCommand cmd = new SqlCommand("SELECT * FROM table1 WHERE parameter=#identifying_parameter", con))
{
cmd.Parameters.AddWithValue("#identifying_parameter", "example");
con.Open();
SqlDataReader reader = cmd.ExecuteReader();
if (reader.Read())
{
attribute1 = Convert.ToString(reader["attribute1"]);
attribute2 = Convert.ToString(reader["attribute2"]);
attribute3 = Convert.ToString(reader["attribute3"]);
.....
}
con.Close();
}
}
using (SqlConnection con = new SqlConnection("user id=user_2;password=pwd;server=serverstring;Trusted_Connection=yes;database=database;connection timeout=30"))
{
using (SqlCommand cmd = new SqlCommand("INSERT INTO table2 (attribute1, attribute2, attribute3, ...) VALUES(#attribute1, #attribute2, #attribute3, ...)", con))
{
cmd.Parameters.AddWithValue("#attribute1", attribute1);
cmd.Parameters.AddWithValue("#attribute2", attribute2);
cmd.Parameters.AddWithValue("#attribute3", attribute3);
....
con.Open();
SqlDataAdapter da = new SqlDataAdapter(cmd);
da.Fill(result);
con.Close();
da.Dispose();
}
}
Obviously I might have a lot of attributes, so is there a simpler way to set every attribute in the table to be equal in C#?

You can use INSERT..INTO..SELECT
DataTable result = new DataTable();
using (SqlConnection con = new SqlConnection("user id=user_2;password=pwd;server=serverstring;Trusted_Connection=yes;database=database;connection timeout=30"))
{
using (SqlCommand cmd = new SqlCommand(#"INSERT INTO table2 (attribute1, attribute2, attribute3, ...)
SELECT attribute1, attribute2, attribute3 ... FROM table1
WHERE parameter=#identifying_parameter
", con))
{
cmd.Parameters.AddWithValue("#identifying_parameter", "example");
con.Open();
SqlDataAdapter da = new SqlDataAdapter(cmd);
da.Fill(result);
con.Close();
da.Dispose();
}
}
You can use * instead of specifying the column name, although which is not good practice..

In order to make a second Table identical (or "equivalent" as per your definition) to the first one (for certainty let's call it sourceTable), you can use SqlBulkCopy.WriteToServer Method (DataTable)(re: https://msdn.microsoft.com/en-us/library/ex21zs8x%28v=vs.110%29.aspx)
using (SqlConnection YourConnection= new SqlConnection(YourConnectionString))
{
YourConnection.Open();
using (SqlBulkCopy bulkCopy = new SqlBulkCopy(YourConnection))
{
bulkCopy.DestinationTableName = "dbo.YourDestinationTable";
try
{
// Write from the source to the destination.
bulkCopy.WriteToServer(sourceTable);
}
catch (Exception ex) { }
}
}
In order to get a sourceTable you can use the following code snippet:
DataTable sourceTable = SqlReadDB(YourConnString, "SELECT *")
private static DataTable SqlReadDB(string ConnString, string SQL)
{
DataTable _dt;
try
{
using (SqlConnection _connSql = new SqlConnection(ConnString))
{
using (SqlCommand _commandl = new SqlCommand(SQL, _connSql))
{
_commandSql.CommandType = CommandType.Text;
_connSql.Open();
using (SqlCeDataReader _dataReaderSql = _commandSql.ExecuteReader(CommandBehavior.CloseConnection))
{
_dt = new DataTable();
_dt.Load(_dataReaderSqlCe);
_dataReaderSql.Close();
}
}
_connSqlCe.Close();
return _dt;
}
}
catch { return null; }
}
}
Hope this may help.

SQL Server connection in WPF

I have a data base in SQL Server 2008 and connecting it in WPF application.I want to read data from table and show in datagrid. Connection is successfully created but when I show it in grid,it show db error(Exception handling).
This is what I am doing.Thanks in advance.
try
{
SqlConnection thisConnection = new SqlConnection(#"Server=(local);Database=Sample_db;Trusted_Connection=Yes;");
thisConnection.Open();
string Get_Data = "SELECT * FROM emp";
SqlCommand cmd = new SqlCommand(Get_Data);
SqlDataAdapter sda = new SqlDataAdapter(cmd);
DataTable dt = new DataTable("emp");
sda.Fill(dt);
MessageBox.Show("connected");
//dataGrid1.ItemsSource = dt.DefaultView;
}
catch
{
MessageBox.Show("db error");
}
It shows connected when i comment the line sda.Fill(dt);

Your SqlCommand doesn't know you opened the connection- it requires an instance of SqlConnection.
try
{
SqlConnection thisConnection = new SqlConnection(#"Server=(local);Database=Sample_db;Trusted_Connection=Yes;");
thisConnection.Open();
string Get_Data = "SELECT * FROM emp";
SqlCommand cmd = thisConnection.CreateCommand();
cmd.CommandText = Get_Data;
SqlDataAdapter sda = new SqlDataAdapter(cmd);
DataTable dt = new DataTable("emp");
sda.Fill(dt);
dataGrid1.ItemsSource = dt.DefaultView;
}
catch
{
MessageBox.Show("db error");
}

You don't assign the command any connection. You open the connection then create a command, but don't link the two.
Try something like:
SqlConnection conn = new SqlConnection(#"Server(local);Database=Sample_db;Trusted_Connection=Yes;");
conn.Open();
string sql= "SELECT * FROM emp";
SqlCommand cmd = new SqlCommand(sql);
cmd.Connection = conn;
SqlDataAdapter sda = new SqlDataAdapter(cmd);
DataTable dt = new DataTable("emp");
sda.Fill(dt);

Assign Connection Object to SqlCommand Object.
using (SqlConnection connection = new SqlConnection(
connectionString))
{
SqlCommand command = new SqlCommand();
command.Connection = connection;
command.CommandTimeout = 15;
command.CommandType = CommandType.Text;
command.CommandText = queryString;
connection.Open();
//Perfom desired Action
}

Add thisConnection as 2nd parameter in
Sqlcommand cmd = new SqlCommand(Get_Data, thisConnection)
try {
string connectionstring = "#"
Server = (local) Database = Sample_dbTrusted_Connection = Yes;
"";
SqlConnection thisConnection = new SqlConnection(connectionstring);
thisConnection.Open();
string Get_Data = "SELECT * FROM emp";
SqlCommand cmd = new SqlCommand(Get_Data, thisConnection);
SqlDataAdapter sda = new SqlDataAdapter(cmd);`
DataTable dt = new DataTable("emp");
sda.Fill(dt);
MessageBox.Show("connected");
//dataGrid1.ItemsSource = dt.DefaultView;
} catch {
MessageBox.Show("db error");
}

I use this code with Oracle and hope it will help you.
First add reference Oracle.DataAccess then add namespace using Oracle.DataAccess.Client;
And using the following code
try
{
string MyConString = "Data Source=localhost;User Id= yourusername;Password=yourpassword;";
using (OracleConnection connection = new OracleConnection(MyConString))
{
connection.Open();
sqldb1 = "select * from DEMO_CUSTOMERS;";
using (OracleCommand cmdSe1 = new OracleCommand(sqldb1, connection))
{
DataTable dt = new DataTable();
OracleDataAdapter da = new OracleDataAdapter(cmdSe1);
da.Fill(dt);
db1.ItemsSource = dt.DefaultView;
}
connection.Close();
}
catch (Exception ex)
{
MessageBox.Show(ex.ToString());
}
XAML code:
<DockPanel>
<DataGrid Margin="10.0" DockPanel.Dock="Left" Name="db1" AutoGenerateColumns="True" >
</DataGrid>
</DockPanel>

public DataTable Execute(string cmd)
{
bool networkUp = System.Net.NetworkInformation.NetworkInterface.GetIsNetworkAvailable();
if (networkUp)
{
try
{
SqlConnection connection = new SqlConnection("ConnectionString");
SqlCommand command = new SqlCommand(cmd);
using (SqlDataAdapter sda = new SqlDataAdapter())
{
DataTable dt = new DataTable();
sda.SelectCommand = command;
command.Connection = connection;
connection.Open();
sda.Fill(dt);
connection.Close();
if (dt != null && dt.Columns.Count > 0)
return dt;
else
return null;
}
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
return null;
}
}
else
{
Console.WriteLine("Network is disconnect");
return null;
}
return null;
}
or :
public void ExecuteNonQuery(string cmd)
{
bool networkUp = System.Net.NetworkInformation.NetworkInterface.GetIsNetworkAvailable();
if (networkUp)
{
try
{
SqlConnection connection = new SqlConnection("ConnectionString");
SqlCommand command = new SqlCommand(cmd);
command.Connection = connection;
connection.Open();
command.ExecuteNonQuery();
connection.Close();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
}
}

DataSet Insert into tables

Is that possible to insert into SQL with DataSet input ?
I have created my DataSet like this :
SqlCommand comm_SelectAll = new SqlCommand(sql_SelectAll, connectionWrapper.conn);
comm_SelectAll.Parameters.AddWithValue("#NO_CLIENT", IdClient);
if (Anne != "")
comm_SelectAll.Parameters.AddWithValue("#DATE_PERIMER", Anne);
SqlDataAdapter adapt_SelectAll = new SqlDataAdapter();
adapt_SelectAll.SelectCommand = comm_SelectAll;
DataSet dSet_SelectAll = new DataSet();
adapt_SelectAll.Fill(dSet_SelectAll);
dSet_SelectAll.Dispose();
adapt_SelectAll.Dispose();
Now I want to insert data into SQL table xx, how can I do that ?
Thanks you in advance

You can try like this ...with out using dataset
public static string BuildSqlNativeConnStr(string server, string database)
{
return string.Format("Data Source={0};Initial Catalog={1};Integrated Security=True;", server, database);
}
private void simpleButton1_Click(object sender, EventArgs e)
{
const string query = "Insert Into Employees (RepNumber, HireDate) Values (#RepNumber, #HireDate)";
string connStr = BuildSqlNativeConnStr("apex2006sql", "Leather");
try
{
using (SqlConnection conn = new SqlConnection(connStr))
{
conn.Open();
using (SqlCommand cmd = new SqlCommand(query, conn))
{
cmd.Parameters.Add(new SqlParameter("#RepNumber", 50));
cmd.Parameters.Add(new SqlParameter("#HireDate", DateTime.Today));
cmd.ExecuteNonQuery();
}
}
}
catch (SqlException)
{
System.Diagnostics.Debugger.Break();
}
}