SQL Server connection in .net - asp.net

Question

Here is my code.
public Dataset ReturnDataset()
{
SqlConnection con = new SqlConnection(Proper connectionstring);
SqlCommand cmd = new SqlCommand(spname,con);
Dataset ds = new Dataset();
try
{
con.Open();
cmd.CommandType = CommandType.StoreProcedure;
SqlDataAdapter da = new SqlDataAdapter(cmd);
da.Fill(ds,table);
return ds;
}
catch (TimeoutException Ex)
{
con.Close();
if (Ex.Message.Contains("Timeout expired"))
{
ds = null;
return ds;
}
else
{
throw;
}
}
catch (Exception)
{
throw;
}
Does I need to write finally clause to close connection if error occur or not?In first try block I closed connection and then throw exception.Does I need to do same in second block?What will happen If already closed connection and trying to close once again?

Answer 1

It is always good idea to close your connection on finally part of try catch as below, or use using statment and let .net to take care of it :
try{
}
catch{
}
finally{
conn.close();
}
or use using :
using (SqlConnection connection = new SqlConnection(connectionString))
{
}
You can close on error too. If you are worried about the state of connection before closing you can check if it is open and close it in finally:
if (conn != null && conn.State == ConnectionState.Open)
{
conn.close();
}

Answer 2

If not strictly necessary I avoid to create a structured catch cascade.
If necessary, I always try to define a catch cascade from the more specific exception to the more generic exception.
I always put any cleanup logic in the finally block:
SqlConnection con = new SqlConnection(Proper connectionstring);
SqlCommand cmd = new SqlCommand(spname,con);
Dataset ds = new Dataset();
try
{
con.Open();
cmd.CommandType = CommandType.StoreProcedure;
SqlDataAdapter da = new SqlDataAdapter(cmd);
da.Fill(ds,table);
return ds;
}
catch(TimeoutException toEx)
{
//manage or log specific exception
}
catch(Exception ex)
{
//manage or log generic exception
}
finally
{
//cleanup
con.Close();
ds = null;
}

Answer 3

I would rewrite your code to be something like this:
public DataSet ReturnDataset()
{
// initialize return value
DataSet result = null;
// put SqlConnection and SqlCommand into using () { ....} blocks to ensure proper disposal
using (SqlConnection con = new SqlConnection(Proper connectionstring))
using (SqlCommand cmd = new SqlCommand(spname, con))
{
result = new DataSet();
try
{
con.Open();
// you had a typo: it's a StoredProcedure - not a StoreProcedure
cmd.CommandType = CommandType.StoredProcedure;
SqlDataAdapter da = new SqlDataAdapter(cmd);
da.Fill(result, table);
con.Close();
}
catch (TimeoutException Ex)
{
if (Ex.Message.Contains("Timeout expired"))
{
result = null;
}
else
{
throw;
}
}
}
// return the result - null if an error happened, a valid DataSet otherwise
return result;
}
Points I improved:
declare the possible return value at the beginning, return only once at the very end
removed unnecessary "catch" on an exception you don't do anything with -> just let it happen
put SqlConnection and SqlCommand into using(...) { ... } blocks to ensure proper and speedy disposal

Answer 4

Why don't you use the Using Statement that ensures a proper closing and disposing of the disposable objects? I think you don't need to catch the exceptions at this level, just let them bubble up and, if needed take care of them at the upper level
Here you can simply
public Dataset ReturnDataset()
{
Dataset ds = new Dataset();
using(SqlConnection con = new SqlConnection(Proper connectionstring))
using(SqlCommand cmd = new SqlCommand(spname,con))
{
con.Open();
cmd.CommandType = CommandType.StoreProcedure;
using(SqlDataAdapter da = new SqlDataAdapter(cmd))
{
da.Fill(ds,table);
}
}
return ds;
}
If this code raises an exception the dataset will be never returned and being a local variable will be quickly become eligible for garbage collection

Answer 5

A better option is to use the using keyword, that does the closing / disposing for you
public Dataset ReturnDataset()
{
using (SqlConnection con = new SqlConnection(connectionstring))
using (SqlCommand cmd = new SqlCommand(spname,con))
{
Dataset ds = new Dataset();
try
{
con.Open();
cmd.CommandType = CommandType.StoreProcedure;
SqlDataAdapter da = new SqlDataAdapter(cmd);
da.Fill(ds,table);
}
catch (TimeoutException Ex)
{
ds = null;
}
return ds;
}
}