Develop Reference

Exception Error in trying to update database using asp.net

How come I'm getting this error while trying to update my database?
ExecuteNonQuery requires an open and available Connection. The connection's current state is closed
Here is the code:
cmd1 = new SqlCommand("UPDATE [guitarBrands] SET type = #type, name = #name, image = #image WHERE id = #id", con1);
con1.Open();
cmd1.Parameters.Add(new SqlParameter("type", newType.Text));
cmd1.Parameters.Add(new SqlParameter("name", newName.Text));
cmd1.Parameters.Add(new SqlParameter("image", newImage.Text));
cmd1.Parameters.Add(new SqlParameter("id", id));
cmd1.ExecuteNonQuery();
con1.Close();
cmd1.Parameters.Clear();
cmd = new SqlCommand("UPDATE [guitarItems] SET brand = #brand WHERE id = #id", con1);
con.Open();
cmd.Parameters.Add(new SqlParameter("brand", newName.Text));
cmd.Parameters.Add(new SqlParameter("id", id));
cmd.ExecuteNonQuery();
con.Close();
cmd.Parameters.Clear();

To avoid these sort of issues, it is recommended you utilize the tower of power.
using(var connection = new SqlConnection(dbConnection))
{
connection.Open();
using(var command = new SqlCommand(query, connection)
{
}
using(var command = new SqlCommand(query, connection)
{
}
}
So the beauty of the tower of power, the using block will implement via within the given code block. So this will make it clear, that both these commands are utilizing the same connection from the using. Also, once the code is out of scope it will implement the IDispose, which will call the garbage collector to free up your resources.
Also, should you choose. The SqlCommand, accepts a parameter array. So if you utilize a method call, you could simply do:
public static GetExample(string query, params SqlParameter[] parameters)
{
using(var connection = new SqlConnection("YourDbConnection"))
using(var command = new SqlCommand("YourQuery", connection))
{
connection.Open();
if(parameters != null)
if(parameters.Any())
command.Parameters.Add(parameters);
command.ExecuteNonQuery();
}
}
I can't recall if the collection is a add, add range, or concat. But either way the option exist.

cmd = new SqlCommand("UPDATE [guitarItems] SET brand = #brand WHERE id = #id", con1);
replace this line to this
cmd = new SqlCommand("UPDATE [guitarItems] SET brand = #brand WHERE id = #id", con);

In your code you use Connexion "con1" in both Commands "cmd1" and "cmd". It is OK to use just one connexion for both commands but then you should leave the connexion open until both command are executed.
In your case you choose to use a new connexion "con" for the second command but you reopen "con1".
So you get an error because "con" is never opened.

C# and sql server

I've created a database and a table with 2 fields Id and Name.
Now I want to insert values on clicking a button the sammple code is given. it's not working.
using (SqlConnection connection = new SqlConnection(strConnection))
{
SqlCommand command =new SqlCommand("insert into Test (Id,Name) values(5,kk);",connection);
connection.Open();
command.ExecuteNonQuery();
connection.Close();
}

String values should be in quotes. This has not much to do with C#, more with T-SQL
Try this, and notice the kk;
SqlCommand command =
new SqlCommand("insert into Test (Id,Name) values(5,'kk');",connection);
connection.Open();
command.ExecuteNonQuery();
connection.Close();
Also I am assuming here that Id is not an auto-increment field. If it is, then you should not fill it.
As a side-node you should look at parameterized queries to prevent SQL injection.

In this instance, you need single quotes ' around the kk
insert into Test (Id,Name) values(5,'kk')
In general, you should use parameterised queries

try this:
SqlConnection conn = new SqlConnection();
SqlTransaction trans = conn.BeginTransaction();
try
{
using (SqlCommand cmd = new SqlCommand("insert into Test (Id,Name) values(#iD, #Name)", conn, trans))
{
cmd.CommandType = CommandType.Text;
cmd.AddParameter(SqlDbType.UniqueIdentifier, ParameterDirection.Input, "#iD", ID);
cmd.AddParameter(SqlDbType.VarChar, ParameterDirection.Input, "#Name", Name);
cmd.ExecuteNonQuery();
}
conn.CommitTransaction(trans);
}
catch (Exception ex)
{
conn.RollbackTransaction(trans);
throw ex;
}

Try this:
SqlConnection con = new SqlConnection('connection string here');
string command = "INSERT INTO Test(Id, Name) VALUES(5, 'kk')";
SqlCommand cmd = new SqlCommand();
cmd.Connection = con;
cmd.CommandType = System.Data.CommandType.Text;
cmd.CommandText = command;
con.Open();
cmd.ExecuteNonQuery();
con.Close();

String values should be between ' '
Verify your connection string
//add your connection string between ""
string connectionString = "";
using (var conn = new SqlConnection(connectionString))
using (DbCommand cmd = conn.CreateCommand())
{
cmd.CommandText = "INSERT INTO pdf (Id, Name) VALUES (5, 'kk')";
conn.Open();
conn.ExecuteNonQuery();
conn.Close();
}

It looks like you have multiple problems with your current code.
You need to enclose string values in single quotes, as pointed out in other answers.
You need to enable remote connection to your SQL server.
Check the following link if you are using SQL server 2008.
How to enable remote connections in SQL Server 2008?
and for SQL Server 2005 see:
How to configure SQL Server 2005 to allow remote connections

Retrieve number of columns in SQL Table - C#

I'm very new to C#. I'm trying to retrieve the number of columns using:
SELECT count(*) FROM sys.columns
Could you please explain how to use the command and put it into a variable.

To connect to the database you can use the SqlConnection class and then to retrieve the Row Count you can use the Execute Scalar function. An example from MSDN:
cmd.CommandText = "SELECT count(*) FROM sys.columns;";
Int32 count = (Int32) cmd.ExecuteScalar();
http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlcommand.executescalar.aspx
http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlconnection

You will need to use ExecuteScalar as the others have said. Also, you will need to filter your SELECT on the object_id column to get the columns in a particular table.
SELECT count(*) FROM sys.columns WHERE object_id = OBJECT_ID(N'table_name')
Alternatively, you could do worse than familiarise yourself with the ANSI-standard INFORMATION_SCHEMA views to find the same information in a future-proof, cross-RDBMS way.

You have to use a command and retrieve back the scalar variable :
SqlCommand cmd = new SqlCommand(sql, conn);
Int32 count = (Int32)cmd.ExecuteScalar();

string connectionString =
"Data Source=(local);Initial Catalog=Northwind;"
+ "Integrated Security=true";
// Provide the query string with a parameter placeholder.
string queryString =
"SELECT Count(*) from sys.columns";
// Specify the parameter value.
int paramValue = 5;
// Create and open the connection in a using block. This
// ensures that all resources will be closed and disposed
// when the code exits.
using (SqlConnection connection =
new SqlConnection(connectionString))
{
// Create the Command and Parameter objects.
SqlCommand command = new SqlCommand(queryString, connection);
// Open the connection in a try/catch block.
// Create and execute the DataReader, writing the result
// set to the console window.
try
{
connection.Open();
SqlDataReader reader = command.ExecuteReader();
while (reader.Read())
{
Console.WriteLine("\t{0}",
reader[0]);
}
reader.Close();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
Console.ReadLine();
}

use Executescalar() for getting a single element.
using (SqlConnection con = new SqlConnection(ConnectionString)) //for connecting to database
{
con.Open();
try
{
using (SqlCommand getchild = new SqlCommand("select count(*) from table1 ", con)) //SQL queries
{
Int32 count = (Int32)getchild.ExecuteScalar();
}
}
}

Use ExecuteScalar
Executes the query, and returns the first column of the first row in the result set returned by the query. Additional columns or rows are ignored.
Int32 colnumber = 0;
string sql = "SELECT count(*) FROM sys.columns";
using (SqlConnection conn = new SqlConnection(connString))
{
SqlCommand cmd = new SqlCommand(sql, conn);
try
{
conn.Open();
colnumber = (Int32)cmd.ExecuteScalar();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
}

You'll want to use the ADO .NET functions in the System.Data.SqlClient namespace. ExecuteScalar is an easy-to-use method when you only want to get a single result. For multiple results, you can use a SqlDataReader.
using System.Data.SqlClient;
string resultVar = String.Empty;
string ServerName="localhost";
string DatabaseName="foo";
SqlConnection conn=new SqlConnection(String.Format("Data Source={0};Initial Catalog={1};Integrated Security=SSPI",ServerName,DatabaseName));
SqlCommand cmd=new SqlCommand(Query,conn);
try
{
conn.Open();
}
catch (SqlException se)
{
throw new InvalidOperationException(String.Format(
"Connection error: {0} Num:{1} State:{2}",
se.Message,se.Number, se.State));
}
resultVar = (string)cmd.ExecuteScalar().ToString();
conn.Close();

SQL query to scalar result in C#

In some programming contexts getting a scalar value from a sql query is easy:
RowCount = Connection.Execute("SELECT Count(*) FROM TableA").Fields(0).Value
In C#, given a SqlConnection variable conn that is already open, is there a simpler way to do this same thing without laboriously creating a SqlCommand, a DataReader, and all in all taking about 5 lines to do the job?

SqlCommand has an ExecuteScalar method that does what you want.
cmd.CommandText = "SELECT COUNT(*) FROM dbo.region";
Int32 count = (Int32) cmd.ExecuteScalar();

If you can use LINQ2SQL (or EntityFramework) you can simplify the actual query asking to
using (var context = new MyDbContext("connectionString"))
{
var rowCount = context.TableAs.Count();
}
If LINQ2SQL is an option that has lots of other benefits too compared to manually creating all SqlCommands, etc.

There is ExecuteScalar which saves you at least from the DataReader:
static public int AddProductCategory(string newName, string connString)
{
Int32 newProdID = 0;
string sql =
"INSERT INTO Production.ProductCategory (Name) VALUES (#Name); "
+ "SELECT CAST(scope_identity() AS int)";
using (SqlConnection conn = new SqlConnection(connString))
{
SqlCommand cmd = new SqlCommand(sql, conn);
cmd.Parameters.Add("#Name", SqlDbType.VarChar);
cmd.Parameters["#name"].Value = newName;
try
{
conn.Open();
newProdID = (Int32)cmd.ExecuteScalar();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
}
return (int)newProdID;
}
(Example taken from this MSDN documentation article)

You do not need a DataReader. This example pulls back the scalar value:
Object result;
using (SqlConnection con = new SqlConnection(ConnectionString)) {
con.Open();
using (SqlCommand cmd = new SqlCommand(SQLStoredProcName, con)) {
result = cmd.ExecuteScalar();
}
}

Investigate Command.ExecuteScalar:
using(var connection = new SqlConnection(myConnectionString))
{
connection.Open();
using(var command = connection.CreateCommand())
{
command.CommandType = CommandType.Text;
command.CommandText = mySql;
var result = (int)command.ExecuteScalar();
}
}
If you're feeling really lazy, encapsulate it all in an extension method, like we do.
EDIT: As requested, an extension method:
public static T ExecuteScalar<T> (this SqlConnection connection, string sql)
{
if (connection == null)
{
throw new ArgumentNullException("connection");
}
if (string.IsNullOrEmpty(sql))
{
throw new ArgumentNullException("sql");
}
using(var command = connection.CreateCommand())
{
command.CommandText = sql;
command.CommandType = CommandType.Text;
return (T)command.ExecuteScalar();
}
}
Note, this version assumes you've properly built the SQL beforehand. I'd probably create a separate overload of this extension method that took two parameters: the stored procedure name and a List. That way, you could protect yourself against unwanted SQL injection attacks.

Simple SQL select in C#?

On my current project, to get a single value (select column from table where id=val), the previous programmer goes through using a datarow, datatable and an sqldatadapter (and of course sqlconnection) just to get that one value.
Is there an easier way to make a simple select query? In php, I can just use mysql_query and then mysql_result and I'm done.
It would be nice if I could just do:
SqlConnection conSql = new SqlConnection(ConnStr);
SomeSqlClass obj = new SomeSqlClass(sql_string, conSql);
conSql.Close();
return obj[0];
Thanks for any tips.

You can skip the DataReader and the DataAdapter and just call ExecuteScalar() on the sql command.
using (SqlConnection conn = new SqlConnection(connString))
{
SqlCommand cmd = new SqlCommand("SELECT * FROM whatever
WHERE id = 5", conn);
try
{
conn.Open();
newID = (int)cmd.ExecuteScalar();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
}

You are probably looking for SqlCommand and SqlDataReader
Dictionary<int, string> users = new Dictionary<int, string>();
using(SqlConnection connection = new SqlConnection("Your connection string"))
{
string query = "SELECT UserId, UserName FROM Users";
SqlCommand command = new SqlCommand(query, connection);
connection.Open();
using (SqlDataReader reader = command.ExecuteReader())
{
while (reader.Read())
users.Add(reader.GetInt32(0), reader.GetString(1));
}
connection.Close();
}

Actually, there is a method SqlCommand.ExecuteScalar() that will simply return the first field from the first row of the returned results. Just for you.
.NET Framework Class Library
SqlCommand..::.ExecuteScalar Method
Executes the query, and returns the first column of the first row in the result set returned by the query. Additional columns or rows are ignored.

You can do something very similar:
using (SqlConnection conn = new SqlConnection(ConnStr))
using (SqlCommand cmd = new SqlCommand(sql_string, conn))
{
conn.Open();
return cmd.ExecuteScalar();
}

you can use SqlCommands executeScalar function. Please look at the following link
http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlcommand.executescalar.aspx