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What if i don't close database connection in disconnected mode

I am doing windows forms application with connection to SQL Server (disconnected mode). Every action I handle in my application needs the connection. So I don't know where to close the connection.
I am asking what if i don't close the connection. I know that there is no runtime error that appears. But is there any other error that could appear?

There is a risk that if you are using the same connection for each method, from a private field or GetConnection() method etc.; you could end up trying to read/write when the connection is still open.
This could then throw errors and you could end up in a whole heap of it, if using a live SQL database.
If you can, create a new instance of a connection in a using statement each time you want to access the DB.
Like this:
var connectionString = "YourConnectionStringToTheDB";
var queryString ="YourSQLQueryHere"; // FROM * IN tbl SELECT * etc...
using (SqlConnection connection = new SqlConnection(
connectionString))
{
using (SqlCommand command = new SqlCommand(queryString, connection))
{
command.Connection.Open();
command.ExecuteNonQuery();
}
}
This way it is closed and disposed of when the code runs outside of the using statement's scope.
Notice that the SqlCommand is also in a using statement, as it too can be disposed of.
This is cleaner code and marks the objects for disposal by the Garbage Collector. (Google is your friend) - BIG topic; a lot of stuff to read.
Here is a similar question which gives you some more detail: The C# using statement, SQL, and SqlConnection
EDIT
Better still, you could wrap your SQL code in a try { } catch { } block to handle any errors at runtime.

C# SQL when/how do I close the connection?

I was using this code:
public class SQLConnection : IConnection
{
private SqlConnection _sqlConnection = null;
//bunch of interface implementations for my project
//the destructor
~SQLConnection()
{
if(_sqlConnection != null)
{
if(_sqlConnection.State == ConnectionState.Open)
{
_sqlConnection.Close();
}
_sqlConnection.Dispose();
}
}
}
This was working well until some time ago, when I started receiving this error: Internal .Net Framework Data Provider error 1
After googling a bit, I found this link (the Caution part) and I think that's what's happening to me.
My class was managing the connection state opening and closing each time, but now that it seems I can't manage it this way, is there any other way that I can do this without having to go to every function that I use the connection and call connection.Close() explicitly?

Always use 'using' for safely disposing the connections.
using(var _sqlConnection = new SqlConnection())
{
//code here
_sqlConnection.Open();
}
//Safely disposed.
Also, it is never a good idea to use destructor explicitly in C# code unless you have unmanaged code.

You're probably receiving this error when one code is trying to access SQLConnection that has been already garbage collected. This usually will happen in cases like this one
SqlConnection sqlConn;
using (var sqlConnection = new SqlConnection())
{
sqlConn = sqlConnection;
sqlConnection.Open();
}
sqlConn.Close();
I know this example looks silly as it's overly simplified, but it happens often when programmers tend to share a connection object between Managing Classes. Look for any recent changes in your code. Maybe you're passing an instance of a connection between multiple objects. One of those objects gets Garbage Collected and in turn the connection gets disposed too.

SQL Connection Open Exception

I am working on a project which, up until today, has been fine. However now when I run it and it goes through a few different Stored Procedure calls it is throwing an InvalidOperationException with the message The connection was not closed. The connection's current state is open.
I get that I could put in a check to see if the connection is already open, but this code hasn't changed (it is under Version Control and isn't modified) so I'm looking for other potential explanations.
Could there be some lock in SQL which isn't being released? Is there a process which I should look out for and kill?
I can't really post the code as there is a lot of it, and it is split up into smaller methods which makes it harder to pull out individual items. E.g:
public SqlConnection Connection
{
get
{
this._connection.Open();
return _connection;
}
}
public IDataReader RetrieveRecord(int Id)
{
//SP
SqlCommand cmd = this.Connection.CreateCommand();
cmd.CommandText = "SelectRecord";
cmd.CommandType = CommandType.StoredProcedure;
//Parameters
cmd.Parameters.Add(new SqlParameter("#tID", Id));
//instruct the data reader to close its connection when its Close method is called by passing the CommandBehavior.CloseConnection
return cmd.ExecuteReader(CommandBehavior.CloseConnection);
}
Nothing massively complex, I just don't understand why this connection is now throwing an exception.

The DAL is not stable enough:
You open a Connection that is not closed if something goes wrong in RetrieveRecord.
You should create a new connection inside RetrieveRecord and close it there in a finally block.
Opening a connection is cheap thanks to Connection Pooling.

Problem is with the line
this._connection.Open();
Because you are trying to open an already opened connection.
Try this to check before opening a connection:
if (this._connection.State == ConnectionState.Closed)
this._connection.Open();

Sorted. Two reboots cleared whatever was keeping the connection open.

When you are talking about killing process, I think you know c# well.
You should always use
using()
{
}
Like:
using(SqlConnection con=new SqlConnection("connectionString"))
{
// Do something with con
using(SqlCommand cmd=new SqlCommand("cmdText",con))
{
// Do something with cmd
}
}
You know that SqlCommand and SqlConnection implement IDisposable
So when you put those objects within using, the connection closing and clean up job is automatically done.
No need to close the connection manually in the code, since using will do the work for you.

Safest DB connection in c# ASP.NET

I'm refactoring some old code as we're periodically having connection pool issues on a clients site.
While some code has wrapped DB connections in try/catch blocks I'll be using the using(){} thing (is there a proper term for this?)
So I'd like some clarification on how to use it in our situation to make as few changes as possible.
What we currently have is (mostly) something like this:
SqlConnection sqlConn = new SqlConnection();
SqlCommand sqlCmd = new SqlCommand();
try
{
// DB stuff here
}
finally
{
sqlCmd.Dispose();
sqlConn.Dispose();
}
Some connections aren't wrapped up at all.
So, I'm thinking of changing it to this:
using (SqlConnection ThisConnection = new SqlConnection(ConnectionString))
{
using (SqlCommand sqlCmd = new SqlCommand())
{
sqlCmd.Connection = ThisConnection;
// DB stuff here
}
}
I've tried this and it works. But I know there's a difference between something working and something working well :)
So, a few questions:
If the SqlConnection is assigned to SqlCommand.Connection and I only wrap up the SqlCommand in a using, will the connection be closed and disposed then the SqlCommand is?
If not, is the above code ok? Or should the SqlCommand using be before the SqlConnection or does it not matter?
When the object is disposed at the end of the using is this absolutely guaranteed to close the DB connection?
All feedback greatly appreciated, cheers.

The using approach is preferable; much harder to get it wrong and leave scenarios where objects can escape without being disposed. Unless you have a very specific reason, it should be your default. You can reduce the nesting, though:
using (SqlConnection ThisConnection = new SqlConnection(ConnectionString))
using (SqlCommand sqlCmd = new SqlCommand())
{
sqlCmd.Connection = ThisConnection;
// DB stuff here
}
When the object is disposed at the end of the using is this absolutely guaranteed to close the DB connection?
It will dispose it; the underlying connection (via any of these approaches) will usually still be pooled, though.
Of course, I also submit that the easiest way to do this is to use less code - less to get wrong. For example, I'd be very tempted to use "dapper", which avoids the need to mess with the commands, readers, parameter collections, etc:
int id = 123;
string name = "abc";
using (var conn = new SqlConnection(ConnectionString))
{
conn.Execute("Some TSQL", new { id, name });
}

if you dispose your connection, you need dispose your command, calling Dispose on it will supress the call to the finalizer. Add using command after using conenction
Don't set your command before connection
Yes, because you close your not managed object , who is coonnection
Remark : using bloc is preferred that try catch finally for basic need without custom treatment in catch bloc
msdn sample link : http://msdn.microsoft.com/fr-fr/library/system.data.sqlclient.sqlconnection(v=vs.110).aspx
this article don't treat using command but speak about connection

c# sql what to dispose

I have the code below to query records from a stored procedure but am concerned I may not be disposing what I need to or am disposing when the object would be cleared by the Garbage Collector shortly afterward anyway.
Do I need to dispose the SqlDataReader since it is within the try catch block?
Do I need to run both cmd.Dispose and cmd.Connection.Close or does one infer the other?
Would the garbage collector eventually dispose of all these objects anyway (maybe not timely enough) or do these objects implictly require dispose possibly because of using unmanaged code?
public void GetData(string studentID)
{
SqlCommand cmd = new SqlCommand("sp_stored_proc",
new SqlConnection(Settings.Default.connectionString))
{ CommandType = CommandType.StoredProcedure };
try
{
cmd.Connection.Open();
cmd.Parameters.AddWithValue("#student_id", studentID);
SqlDataReader dr = cmd.ExecuteReader();
//do something with the data
if (dr != null)
dr.Dispose();
}
catch
{
//error handling
}
finally
{
if (cmd != null)
{
cmd.Dispose();
cmd.Connection.Close();
}
}
}

You should dispose the data reader, and the command. No need to separately close the connection if you dispose the command. You should ideally do both using a using block:
using (SqlCommand cmd = new...)
{
// do stuff
using (SqlDataReader dr = cmd.ExecuteReader())
{
// do stuff
}
}
If you need exception handling do that separately either inside or around the using blocks - no need for the finally for the Dispose calls though with using.

If you use something like this:
public void GetData(string studentID)
{
using (SqlConnection connection = new SqlConnection(Settings.Default.connectionString))
{
connection.Open();
using (SqlCommand command = connection.CreateCommand())
{
command.CommandType = CommandType.StoredProcedure;
command.CommandText = "sp_stored_proc";
command.Parameters.AddWithValue("#student_id", studentID);
using (SqlDataReader dataReader = command.ExecuteReader())
{
// do something with the data
}
}
}
}
then all of your Disposable objects will get disposed of correctly. Calling Dispose() on the SqlConnection, SqlCommand and SqlDataReader objects (which is what the using block does when it exits) closes them correctly.
Additionally, this approach keeps all of your variables scoped to where they are used.
The downside to this approach is that if you need error handling using a try/catch, you have to either wrap it around the whole method body, or use several of them to handle connection errors differently from reading errors, etc...

Do I need to dispose the SqlDataReader
since it is within the try catch
block?
-- Yes, as being inside of the try catch will not call the dispose method.
Do I need to run both cmd.Dispose and cmd.Connection.Close or does one infer the other?
-- Yes, you need to run both. Calling Cmd.dispose does not close the connection.
The dispose method is meant to be used by the programmer to clean up resources which either aren't directly managed by the garbage collector, or the need to be cleared out after the program is done using them to free up space. Technically, one could set up the program so the GC would handle it's disposal, but that's an assumption I wouldn't make, especially since the programmer writing the class exposed the dispose method for you. Putting the Command in a using statement is probably the easiest route, because you know it will get disposed when the code leaves the declaration space.
using (var connection = new Connection ())
{
using (var cmd = new Command())
{
}
}

Personally if something has a dispose method then it is worth using it anyway as they will prevent protential memory leaks.

To make a long story short; if it implements IDisposable, you should call Dispose.
Even if you use Reflector to figure out that Dispose in one object invokes Dispose on another object, I would still recommend to call Dispose on both, since this is internal implementation details that may change in some future release, so you should not rely on that always being true.
So, Dispose anything that is IDisposable.

you should open Connection firstly by Connection.Open();
then use the methods such as SqlDataReader to read
after all,close SqlDataReader firstly and then close connection
you can use keyword "using" to dispose it, but it is not a good idea
in fact the keyword "using" is to dispose the object automatically.
in other word,the object should achieve dispose method