Develop Reference

How to actually execute a command?

I'm playing around making a POC and I've created the following call.
public string DoStuff()
{
try
{
using (SqlDataAdapter adapter = new SqlDataAdapter())
{
SqlConnection connection = new SqlConnection("Server...");
string command = "insert into Records values (...)";
adapter.InsertCommand = new SqlCommand(command, connection);
}
}
catch (Exception exception)
{
return exception.Message + " " + exception.InnerException;
}
return "WeeHee!";
}
The text I'm seeing returned is the happy one, so I conclude there's no exceptions. Hence, I conclude that the call to the DB is performed as supposed to. However, there's no new lines in the DB being created.
I'm using the same connection string as I have in my config file and the command in pasted in from SQL Manager, where it works.
So my suspicion was that although I create an insert command, I never actually execute it but according to MSDN that's how it's supposed to work.
What stupid thing do I miss here?

You are missing connection.Open(); and adapter.InsertCommand.ExecuteNonQuery();
using (SqlDataAdapter adapter = new SqlDataAdapter())
{
SqlConnection connection = new SqlConnection("Server...");
connection.Open();
string command = "insert into Records values (...)";
adapter.InsertCommand = new SqlCommand(command, connection);
adapter.InsertCommand.ExecuteNonQuery();
}

You should use ExecuteNonQuery instead. Using an SqlDataAdapter for an INSERT query does not make sense.
Also you should Open your connection just before you execute it.

You can:
using(SqlConnection connection = new SqlConnection("Server..."))
{
SqlCommand command = connection.CreateCommand();
command.CommandText = "insert into Records values (...)";
connection.Open();
int craeted = command.ExecuteNonQuery();
}

The example you linked to returned a SQLAdapter for later use.
You don't need one at all:
using (SqlConnection connection = new SqlConnection("Server..."))
{
string command = "insert into Records values (...)";
connection.Open();
var command = new SqlCommand(command, connection);
command.ExecuteNonQuery();
}
Note that there are other execution methods, depending on expected return values and whether you want asynchronous operation: https://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlcommand(v=vs.110).aspx

Connect to remote oracle database using odac

I need to make asmx web service. I installed ODAC from here
Then, i add references to my project:
1) Oracle.DataAccess
2) Oracle.Web
[WebMethod]
public string EaaTest(string r_object_id)
{
string connString = "Data Source=(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=TCP)" +
"(HOST=my host)(PORT=1521)))(CONNECT_DATA=(SERVER=DEDICATED)(SERVICE_NAME=dcmt)));" +
"User Id=my id ;Password=my password;"
using (OracleConnection conn = new OracleConnection(connString))
{
OracleCommand cmd = new OracleCommand();
cmd.Connection = conn;
cmd.CommandText = string.Format("select DSS_TITLE_RU from DBREP36.DDT_DA_DIRECTION_S where R_OBJECT_ID=0", r_object_id);
cmd.CommandType = CommandType.Text;
OracleDataReader dr = cmd.ExecuteReader();
dr.Read();
string result = dr.GetString(0);
return result;
}
}
Now, i have exception:
An exception of type 'System.InvalidOperationException' occurred in
Oracle.DataAccess.dll but was not handled in user code
Additional information: Connection must be open for this operation
On line: OracleDataReader dr = cmd.ExecuteReader();

Error message isn't clear at all?
Connection must be open for this operation
You need to open your connection before you execute your command.
conn.Open();
OracleDataReader dr = cmd.ExecuteReader();
Use using statement to dispose your command and reader as you did for your connection.
By the way, you didn't specify zero index in your string.Format. Your
where R_OBJECT_ID=0
should be
where R_OBJECT_ID = {0}
As a better option, use parameterized queries. Any kind of string concatenations are open for SQL Injection attacks.
Since you return just first column of the first row, use ExecuteScalar instead which is exactly what this for.
using(var conn = new OracleConnection(connString))
using(var cmd = conn.CreateCommand())
{
cmd.CommandText = #"select DSS_TITLE_RU from DBREP36.DDT_DA_DIRECTION_S
where R_OBJECT_ID = #id";
cmd.Parameters.AddWithValue(#id, r_object_id);
conn.Open();
return (string)cmd.ExecuteScalar();
}

Missing Required Parameter in Parameterized Query?

I am getting the following error trying to execute the code below
No Value Given For One Or More Required Parameters.
string paraName = "CONTROL";
string fullPathToExcel = #"C:\Users\xbbjn2h\Desktop\Mapping.xlsx";
string connString = string.Format(#"Provider=Microsoft.ACE.OLEDB.12.0;Data Source={0};Extended Properties=""Excel 12.0 Xml;HDR=YES;""",fullPathToExcel);
string sql = "SELECT [FUNCTION],[NAME] from [Sheet1$] WHERE [FUNTION] = ?";
OleDbConnection conn = new OleDbConnection();
conn.ConnectionString = connString;
using (OleDbCommand cmd = new OleDbCommand(sql, conn))
{
cmd.Parameters.AddWithValue("?", paraName);
DataSet ds = new DataSet();
conn.Open();
OleDbDataAdapter dab = new OleDbDataAdapter(cmd);
dab.Fill(ds);
dataGridView1.DataSource = ds.Tables[0];
conn.Close();
}

OleDbCommand does not support named parameters (see the docs). What you need to do is something like:
cmd.Parameters.Add(new OleDbParameter { Value = paraName });
Edit: I haven't tried it, but I suppose it might be possible to use your above code and pass null as the name argument...

James, I can see that you are trying to parametrize as you would with SQL. However OleDb wouldn't follow the exact pattern. In OleDb you can simply put question marks in your sql sentence and fill them up later using Parameter.Add().value which is quite straight forward.
As MSDN reference points out:
The OLE DB .NET Provider does not support named parameters for passing
parameters to an SQL statement or a stored procedure called by an
OleDbCommand when CommandType is set to Text.
I have rewritten your code in the way it should look like
string paraName = "CONTROL";
string fullPathToExcel = #"C:\Users\xbbjn2h\Desktop\Mapping.xlsx";
string connString = string.Format(#"Provider=Microsoft.ACE.OLEDB.12.0;Data Source={0};Extended Properties=""Excel 12.0 Xml;HDR=YES;""",fullPathToExcel);
string sql = string.Format("SELECT [{0}],[{1}] from [{2}] WHERE [{0}] = ?", strFunction, strName, strSheetName);
conn.ConnectionString = connString;
using (OleDbConnection conn = new OleDbConnection())
{
OleDbCommand cmd = new OleDbCommand();
cmd.Connection = conn;
cmd.CommandText = sql;
cmd.Parameter.Add("#Param1", OleDbType.VarChar).Value = paraName; // paraName or any value you wish.
DataSet ds = new DataSet();
conn.Open();
OleDbDataAdapter dab = new OleDbDataAdapter(cmd); //or cmd.ExecuteNonQuery(); in Insert sql commands.
dab.Fill(ds);
dataGridView1.DataSource = ds.Tables[0];
conn.Close();
}
Note, You should put your OleDbConnection inside the using statement rather than your OleDbCommand.
I haven't tested it and it may contain some minor error. Other than that punch it there and press play (F5).
You can find more on OleDb parametrization from OleDbCommand.Parameters Property
Good luck and let us know what happens.

How to initialize SelectCommand.Connection property in c#?

Fill: SelectCommand.Connection property has not been initialized. I have done the coding in button click. Conn is my connection class's object. I have called this connection class in my button click class. Let me know why it shows error? I have already searched answer for this question in Stack overflow and I applied even though it shows the same error. The ddcode.selectedItem.Text is dropdown for select Employee name.
string strQuery = "SELECT MachID, EmpCode, FROM LeaveApply where MachID='" + ddcode.SelectedItem.Text + "'",conn;
SqlCommand cmd = new SqlCommand(strQuery);
SqlDataAdapter sda = new SqlDataAdapter(cmd);
DataTable dt = new DataTable();
sda.Fill(dt);
See it is my connection class
public Connection()
{
conn = new SqlConnection(ConfigurationManager.ConnectionStrings["ApplicationServices"].ConnectionString);
cmd = null;
}
And I have called this connection class in my button click function's class like
Connection conn = new Connection();

There's no point actually creating a SqlCommand object because the SqlDataAdapter will do it for you. In fact, it can even create the SqlConnection object for you. If you need to reuse the connection then do this:
using (var connection = new SqlConnection(connectionString))
using (var adapter = new SqlDataAdapter(query, connection))
{
adapter.SelectCommand.Parameters.AddWithValue(paramName, paramValue);
// ...
}
and, if you don't need to reuse the connection then do this:
using (var adapter = new SqlDataAdapter(query, connectionString))
{
adapter.SelectCommand.Parameters.AddWithValue(paramName, paramValue);
// ...
}
If you really want to create a separate SqlCommand then do this:
using (var connection = new SqlConnection(connectionString))
using (var command = new SqlCommand(query, connection))
using (var adapter = new SqlDataAdapter(command))
{
command.Parameters.AddWithValue(paramName, paramValue);
// ...
}

I would recommend using the CreateCommand factory method of the connection object to create your command, then your command object will correctly use the connection object.
SqlConnection conn = new SqlConnection("ConnectionString");
conn.Open(); // Make sure connection is open.
string strQuery = "SELECT MachID, EmpCode, FROM LeaveApply where MachID='" + selectedItem + "'";
SqlCommand cmd = conn.CreateCommand();
cmd.CommandText = strQuery;
SqlDataAdapter sda = new SqlDataAdapter(cmd);
DataTable dt = new DataTable();
sda.Fill(dt);
Alternatively you can manually tell the command to use the connection object
cmd.Connection = conn;
It sounds like jmcilhinney has a better answer for your purposes however.

You are missing the connection to your database. The connection will perform the following jobs.
Create a connection to database by using provided connection string.
Open up the connection bridge to transact the data.
Execute the provided query or Stored Procedure.
Fill the data in application's memory
Close the connection bridge to prevent the database.
Use the object of your own connection class.
Try it as follows:
using (Connection Con = new Connection()) {
SqlCommand cmd = new SqlCommand(strQuery);
cmd.Connection = Con;
SqlDataAdapter sda = new SqlDataAdapter(cmd);
try {
Con.Open();
sda.SelectCommand = cmd;
sda.Fill(dt);
Con.Close();
} catch (Exception ex) {
}

Fetching data from oracle DB

I use the below code to connect to my oracle DB and execute a query. The query I used in the example simply fetches a set of rows from a table. However, I keep getting an error message that "The table or view does not exist". But, I am pretty sure that the table exists in the DB. Where am I going wrong?
public void UpdateDatabase()
{
System.Data.OracleClient.OracleConnection conn = new System.Data.OracleClient.OracleConnection();
conn.ConnectionString = "Data Source=(DESCRIPTION =(ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.5.144)(PORT = 1521))(CONNECT_DATA =(SERVER = DEDICATED)(SERVICE_NAME = orcl)));UID=mwm;PWD=mwm";
conn.Open();
OracleCommand command = conn.CreateCommand();
command.CommandText = "Select * from Task";
command.ExecuteNonQuery();
command.Dispose();
}
The error is triggered when command.ExecuteNonQuery() is reached.

I think the problem is with command.ExecuteNonQuery();
Actually you are executing a query here therefore you should use either DataAdapter or DataReader.
public void UpdateDatabase()
{
System.Data.OracleClient.OracleConnection conn = new System.Data.OracleClient.OracleConnection();
conn.ConnectionString = "Data Source=(DESCRIPTION =(ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.5.144)(PORT = 1521))(CONNECT_DATA =(SERVER = DEDICATED)(SERVICE_NAME = orcl)));UID=mwm;PWD=mwm";
conn.Open();
OracleCommand command = conn.CreateCommand();
SqlDataAdapter a = new SqlDataAdapter("Select * from \"Task\"", command))
DataTable t = new DataTable();
a.Fill(t);
command.Dispose();
}

Task is oracle Reserve Word, that is why you are getting this error. Use double quotes.
command.CommandText = "Select * from \"Task\"";
ExectueNonQuery, may not give you any error, but it will not give you the desired result. You need to do command.ExecuteReader. See the link.
You may also see this Getting Started with Oracle Data Provider for .NET (C# Version)