How do I translate a List<string> into a SqlParameter for a Sql In statement?

Question

I seem to be confused on how to perform an In statement with a SqlParameter. So far I have the following code:

cmd.CommandText = "Select dscr from system_settings where setting in @settings";
cmd.Connection = conn;
cmd.Parameters.Add(new SqlParameter("@settings", settingList));

reader = cmd.ExecuteReader();

settingsList is a List<string>. When cmd.ExecuteReader() is called, I get an ArgumentException due to not being able to map a List<string> to "a known provider type".

How do I (safely) perform an In query with SqlCommands?

Solution 1

You could try something like this:

string sql = "SELECT dscr FROM system_settings WHERE setting IN ({0})";
string[] paramArray = settingList.Select((x, i) => "@settings" + i).ToArray();
cmd.CommandText = string.Format(sql, string.Join(",", paramArray));

for (int i = 0; i < settingList.Count; ++i)
{
    cmd.Parameters.Add(new SqlParameter("@settings" + i, settingList[i]));
}

Solution 2

You appear to be trying to pass a multi valued parameter, that SQL syntax isn't going to do what you expect. You may want to pass a table value parameter.

Read this: http://www.sommarskog.se/arrays-in-sql.html#iter-list-of-strings

specifically: http://www.sommarskog.se/arrays-in-sql-2008.html#ListSqlDataRecord

private static void datatable_example() {

   string [] custids = {"ALFKI", "BONAP", "CACTU", "FRANK"};

   DataTable custid_list = new DataTable();
   custid_list.Columns.Add("custid", typeof(String));

   foreach (string custid in custids) {
      DataRow dr = custid_list.NewRow();
      dr["custid"] = custid;
      custid_list.Rows.Add(dr);
   }

   using(SqlConnection cn = setup_connection()) {
      using(SqlCommand cmd = cn.CreateCommand()) {

         cmd.CommandText =
           @"SELECT C.CustomerID, C.CompanyName
             FROM   Northwind.dbo.Customers C
             WHERE  C.CustomerID IN (SELECT id.custid FROM @custids id)";
         cmd.CommandType = CommandType.Text;

         cmd.Parameters.Add("@custids", SqlDbType.Structured);
         cmd.Parameters["@custids"].Direction = ParameterDirection.Input;
         cmd.Parameters["@custids"].TypeName = "custid_list_tbltype";
         cmd.Parameters["@custids"].Value = custid_list;

         using (SqlDataAdapter da = new SqlDataAdapter(cmd))
         using (DataSet        ds = new DataSet()) {
            da.Fill(ds);
            PrintDataSet(ds);
         }
      }
   }
}