Is this defensive code or are there possibilities that it could encouter problems?

问题

I've got the following code which makes a connection to a db > runs a stored proc > and then moves on.

I believe it is easy to get db programming wrong so it is important to be defensive: is the following defensive? (or can it be improved?)

public int RunStoredProc()
{
SqlConnection conn = null;
SqlCommand dataCommand = null;
SqlParameter param = null;
int myOutputValue;

try
{
    conn = new SqlConnection(ConfigurationManager.ConnectionStrings["IMS"].ConnectionString);                  
    conn.Open();
    dataCommand = conn.CreateCommand();
    dataCommand.CommandType = CommandType.StoredProcedure;
    dataCommand.CommandText = "pr_blahblah";
    dataCommand.CommandTimeout = 200; //seconds
    param = new SqlParameter();
    param = dataCommand.Parameters.Add("@NumRowsReturned", SqlDbType.Int);
    param.Direction = ParameterDirection.Output;
    dataCommand.ExecuteNonQuery();
    myOutputValue = (int)param.Value;

    return myOutputValue;
}
catch (SqlException ex)
{
    MessageBox.Show("Error:" + ex.Number.ToString(), "Error StoredProcedure");
    return 0;
}
finally
{
    if (conn != null)
    {
        conn.Close();
        conn.Dispose();
    }
}
}

CODE NOW LOOKS LIKE THE FOLLOWING

I've tried to use all the help offered by everyone and the above code has now been amended to the following which I hope is now sufficiently defensive:

public SqlConnection CreateConnection()
{
    SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["IMS"].ConnectionString);
    return conn;
}
public int RunStoredProc()
{
    using (var conn = CreateConnection())
    using (var dataCommand = conn.CreateCommand()) 
    {
            conn.Open();
            dataCommand.CommandType = CommandType.StoredProcedure;
            dataCommand.CommandText = "pr_BankingChargebacks";
            dataCommand.CommandTimeout = 200; //5 minutes
            SqlParameter param = new SqlParameter();
            param = dataCommand.Parameters.Add("@NumRowsReturned", SqlDbType.Int);
            param.Direction = ParameterDirection.Output;
            dataCommand.ExecuteNonQuery();
            int myOutputValue = (int)param.Value;

            return myOutputValue;

    } 
}

回答1:

Try using, well, the using construct for such things.

using(var conn = new SqlConnection(ConfigurationManager.ConnectionStrings["IMS"].ConnectionString)
{
}

Once you do that, I think you will be at the right level of "defense". Similarly try to do the same for anything that has to be disposed ( like the command)

回答2:

There is no need to call both .Close() and .Dispose()
Prefer the using block instead of try-finally
Dispose of the command object
I would remove the catch clause. It doesn't belong here (though YMMV).

If you are going to write this code all over the place, stop. At least create a small helper class to do this, or use a light-weight 'ORM' like Massive, Dapper or PetaPoco. For an example of an ADO.Net helper class, see https://github.com/jhgbrt/yadal/blob/master/Net.Code.ADONet.SingleFile/Db.cs.

回答3:

The main thing I would notice is a MessageBox in database-access code. I can't think of a single scenario that is useful. Just let the exception rise. Don't catch that.

As a general template:

using(var conn = CreateConnection())
using(var cmd = conn.CreateCommand())
{
    // setup cmd and the parameters
    conn.Open();
    cmd.ExecuteNonQuery();
    // post-process cmd parameters (out/return/etc)
}

Note: no Close(), no catch; all the finally are handled by the using. Much simpler; much harder to get wrong.

Another thing to emphasise is the use of a factory method for creating the connection; don't put:

new SqlConnection(ConfigurationManager.ConnectionStrings["IMS"].ConnectionString)

into every method; after all... that could change, and it is unnecessary repetition.

回答4:

If MessageBox.Show("Error:" + ex.Number.ToString(), "Error StoredProcedure"); is how you're going to handle an exception then you're not logging or even retrieving the actual exception details.

回答5:

In addition to manojlds's advice I recommend that you make yourself some reusable helper methods to call the database. For example, make yourself a method that reads the connection string, creates the connection and opens it. Don't repeat infrastructure stuff everywhere.

You can do the same for invoking an sproc or a command text.

来源：https://stackoverflow.com/questions/11687146/is-this-defensive-code-or-are-there-possibilities-that-it-could-encouter-problem

标签

sql-server-2008-r2