Question

I am creating a small helper function to return a DataTable. I would like to work across all providers that ADO.Net supports, so I thought about making everything use IDbCommand or DbCommand where possible.

I have reached a stumbling block with the following code:

    private static DataTable QueryImpl(ref IDbConnection conn, String SqlToExecute, CommandType CommandType, Array Parameters)
    {
        SetupConnection(ref conn);
        // set the capacity to 20 so the first 20 allocations are quicker...
        DataTable dt = new DataTable();
        using (IDbCommand cmd = conn.CreateCommand())
        {
            cmd.CommandText = SqlToExecute;
            cmd.CommandType = CommandType;
            if (Parameters != null && Parameters.Length > 0)
            {
                for (Int32 i = 0; i < Parameters.Length; i++)
                {
                    cmd.Parameters.Add(Parameters.GetValue(i));
                }
            }
            dt.Load(cmd.ExecuteReader(), LoadOption.OverwriteChanges);
        }
        return dt;
    }

When this code is executed, I receive an InvalidCastException which states the following:

The SqlParameterCollection only accepts non-null SqlParameter type objects, not String objects.

The code falls over on the line:

cmd.Parameters.Add(Parameters.GetValue(i));

Any ideas?

Any improvements to the above code is appreciated.

---

Actual solution:

    private static readonly Regex regParameters = new Regex(@"@\w+", RegexOptions.Compiled);
    private static DataTable QueryImpl(ref DbConnection conn, String SqlToExecute, CommandType CommandType, Object[] Parameters)
    {
        SetupConnection(ref conn);
        DataTable dt = new DataTable();
        using (DbCommand cmd = conn.CreateCommand())
        {
            cmd.CommandText = SqlToExecute;
            cmd.CommandType = CommandType;
            if (Parameters != null && Parameters.Length > 0)
            {
                MatchCollection cmdParams = regParameters.Matches(cmd.CommandText);
                List<String> param = new List<String>();
                foreach (var el in cmdParams)
                {
                    if (!param.Contains(el.ToString()))
                    {
                        param.Add(el.ToString());
                    }
                }
                Int32 i = 0;
                IDbDataParameter dp;
                foreach (String el in param)
                {
                    dp = cmd.CreateParameter();
                    dp.ParameterName = el;
                    dp.Value = Parameters[i++];
                    cmd.Parameters.Add(dp);
                }
            }
            dt.Load(cmd.ExecuteReader(), LoadOption.OverwriteChanges);
        }
        return dt;
    } 

Thanks for ideas/links etc. 🙂

Answer 1

I believe IDbCommand has a CreateParameter() method:

var parameter = command.CreateParameter();
parameter.ParameterName = "@SomeName";
parameter.Value = 1;

command.Parameters.Add(parameter);