How to Close a DataReader on Exception

Question

I have the following code in some methods of my Data Layer:

StringBuilder sb = new StringBuilder();
SqlCommand s = new SqlCommand(sb.ToString(), conn);
try 
{ 
    SqlDataReader dr = s.ExecuteReader(); 
    while(dr.Read())
      DoSomething(dr);
}
catch (Exception ex)
{ 
    sb.Append(Util.ExceptionRecursive(ex)); 
}

The thing is, dr never closes in case of exception. And when other method tries to access another data reader, it throws another exception that says something like "Another Datareader is connected to the Database"

I want to close my DataReader in any case. But this:

sb = new StringBuilder();
SqlCommand s = new SqlCommand(sb.ToString(), conn);
SqlDataReader dr;
try 
{
    dr = s.ExecuteReader(); 
    while(dr.Read())
      DoSomething(dr);
}
catch (Exception ex)
{ 
    sb.Append(Util.ExceptionRecursive(ex)); 
}
finally
{
    dr.Close();
}

Won't work because in case of exception dr may have no data, and won't compile.

How should I do it then?

Answer 1

You should use the using statement :
It generates a finally block to ensure that your resource is always disposed.

StringBuilder sb = new StringBuilder();
using (SqlCommand s = new SqlCommand(sb.ToString(), conn)) {
    try 
    { 

        using (SqlDataReader dr = s.ExecuteReader()) {
            while(dr.Read())
              DoSomething(dr);
        }

    }
    catch (Exception ex)
    { 
        sb.Append(Util.ExceptionRecursive(ex)); 
    }    
}

Answer 2

The best way is probably this:

sb = new StringBuilder();
...
using (SqlCommand s = new SqlCommand(sb.ToString(), conn))
using (SqlDataReader dr = s.ExecuteReader())
{
    try
    {
        while(dr.Read())
          DoSomething(dr);
    }
    catch (Exception ex)
    { 
        sb.Append(Util.ExceptionRecursive(ex)); 
    }
}

However, if you're expecting (or not) exceptions during SQL execution, you must place the exception handling code outside:

sb = new StringBuilder();
...
try
{
    using (SqlCommand s = new SqlCommand(sb.ToString(), conn))
    using (SqlDataReader dr = s.ExecuteReader())
    {
        while(dr.Read())
          DoSomething(dr);
    }
}
catch (Exception ex)
{ 
    sb.Append(Util.ExceptionRecursive(ex)); 
}

Answer 3

you can write it as:

if(dr!=null) dr.Close();