Month: March 2017

IBM Data Server Provider (DB2) .Net Tips – Series 1

I’ve been working with IBM Informix lately and from my previous post, I’ve mentioned a couple of ways to work with Informix. Now that I’ve settled with strictly using DB2 (see my previous post on this), my colleagues and I have been developing abstractions to work with Informix via Entity Framework and/or DB2 SDK (IBM’s version).

So, you’ve just been asked to tackle some data access tasks through Informix via .Net? My colleague, Jeff Crose (https://www.linkedin.com/in/jeff-crose-419797/) came out with some really cool tips worth blogging about. Jeff is a distinguished software developer in our team, working with backend data development through database platforms such as SQL Server and Informix. Shout out to Jeff for coming up with these tips!

TIP: Informix Overloaded Stored Procedures

Unlike other relational database management systems, Informix supports overloaded stores procedures. That may not seem like a big deal, but it can lead you astray if you’re not careful. Consider the following sample:

try
{
    using (DB2Connection conn = new DB2Connection(connectionString))
    {
        conn.Open();

        using (DB2Command cmd = conn.CreateCommand())
        {
            cmd.CommandType = CommandType.Text;
            cmd.CommandText = "EXECUTE PROCEDURE customer_insert_overload(?, ?, ?)";

            cmd.Parameters.Add(new DB2Parameter("customername", DB2Type.VarChar, 30)).Value = "George Washington";
            cmd.Parameters.Add(new DB2Parameter("customerstate", DB2Type.Char, 2)).Value = "WA";
            cmd.Parameters.Add(new DB2Parameter("customerinfo", DB2Type.Text)).Value = "The first President of the United States";

            var customerid = cmd.ExecuteScalar();
Console.WriteLine("customerid: {0}", customerid);
        }
    }
}
catch (DB2Exception exception)
{
    Console.WriteLine("Error Message: {0}", exception.Message);
}

You’ve created the connection, created the command, and created parameters of the correct types to match the signature of the stored procedure but you receive the following error message: ERROR[IX000][IBM][IDS / UNIX64] Routine(customer_insert_overload) cannot be resolved. As it turns out, the issue is not with the overload but with the fact that one of the parameters is a TEXT type. To get past the error, you need to explicitly cast the parameter to TEXT in the CommandText property.

try
{
    using (DB2Connection conn = new DB2Connection(connectionString))
    {
        conn.Open();

        using (DB2Command cmd = conn.CreateCommand())
        {
            cmd.CommandType = CommandType.Text;
            cmd.CommandText = "EXECUTE PROCEDURE customer_insert_overload(?, ?, ?::TEXT)";

            cmd.Parameters.Add(new DB2Parameter("customername", DB2Type.VarChar, 30)).Value = "George Washington";
            cmd.Parameters.Add(new DB2Parameter("customerstate", DB2Type.Char, 2)).Value = "WA";
            cmd.Parameters.Add(new DB2Parameter("customerinfo", DB2Type.Text)).Value = "The first President of the United States";

            var customerid = cmd.ExecuteScalar();
Console.WriteLine("customerid: {0}", customerid);
        }
    }
}
catch (DB2Exception exception)
{
    Console.WriteLine("Error Message: {0}", exception.Message);
}

TIP: ExecuteScalar VS ExecuteNonQuery

Now that the code works, you may be wondering why the ExecuteScalar method was chosen over ExecuteNonQuery for an insert. In this case, the stored procedure returns the identity for the newly inserted row. Even though the stored procedure returns an integer, it does not behave like its SQL Server counterpart. The following code inserts the data successfully but does not return a value.

try
{
    using (DB2Connection conn = new DB2Connection(connectionString))
    {
        conn.Open();

        using (DB2Command cmd = conn.CreateCommand())
        {
            cmd.CommandType = CommandType.Text;
            cmd.CommandText = "EXECUTE PROCEDURE customer_insert_overload(?, ?, ?::TEXT)";

            cmd.Parameters.Add(new DB2Parameter("customername", DB2Type.VarChar, 30)).Value = "Andrew Jackson";
            cmd.Parameters.Add(new DB2Parameter("customerstate", DB2Type.Char, 2)).Value = "MS";
            cmd.Parameters.Add(new DB2Parameter("customerinfo", DB2Type.Text)).Value = "The seventh President of the United States";
            cmd.Parameters.Add(new DB2Parameter("customerid", DB2Type.Integer));
            cmd.Parameters["customerid"].Direction = ParameterDirection.ReturnValue;

            cmd.ExecuteNonQuery();
            var customerid = cmd.Parameters["customerid"].Value;

Console.WriteLine("customerid: {0}", customerid);
        }
    }
}
catch (DB2Exception exception)
{
    Console.WriteLine("Error Message: {0}", exception.Message);
}

To get the “customerid” you need to use the ExcecuteScalar method.

TIP: ExecuteRow for multiple return values

What if the stored procedure returns multiple values? The ExecuteRow method can be used to get all the values.

try
{
    using (DB2Connection conn = new DB2Connection(connectionString))
    {
        conn.Open();

        using (DB2Command cmd = conn.CreateCommand())
        {
            cmd.CommandType = CommandType.Text;
            cmd.CommandText = "EXECUTE PROCEDURE customer_insert(?, ?, ?::TEXT)";

            cmd.Parameters.Add(new DB2Parameter("customername", DB2Type.VarChar, 30)).Value = "Abraham Lincoln";
            cmd.Parameters.Add(new DB2Parameter("customerstate", DB2Type.Char, 2)).Value = "NE";
            cmd.Parameters.Add(new DB2Parameter("customerinfo", DB2Type.Text)).Value = "The sixteenth President of the United States";

            var row = cmd.ExecuteRow();
Console.WriteLine("customerid: {0}, result: {1}", row[0], row[1]);
        }
    }
}
catch (DB2Exception exception)
{
    Console.WriteLine("Error Message: {0}", exception.Message);
}

Notice that the “customerinfo” parameter was once again explicitly cast to a TEXT type in the CommandText property. The following example will once again cause the “ERROR[IX000][IBM][IDS / UNIX64] Routine(customer_insert) can not be resolved.” exception.

try
{
    using (DB2Connection conn = new DB2Connection(connectionString))
    {
        conn.Open();

        using (DB2Command cmd = conn.CreateCommand())
        {
            cmd.CommandType = CommandType.Text;
            cmd.CommandText = "EXECUTE PROCEDURE customer_insert(?, ?, ?)"; 

            cmd.Parameters.Add(new DB2Parameter("customername", DB2Type.VarChar, 30)).Value = "Abraham Lincoln";
            cmd.Parameters.Add(new DB2Parameter("customerstate", DB2Type.Char, 2)).Value = "NE";
            cmd.Parameters.Add(new DB2Parameter("customerinfo", DB2Type.Text)).Value = "The sixteenth President of the United States";

            var row = cmd.ExecuteRow();
Console.WriteLine("customerid: {0}, result: {1}", row[0], row[1]);
        }
    }
}
catch (DB2Exception exception)
{
    Console.WriteLine("Error Message: {0}", exception.Message);
}

 

TIP: And Finally, the “ExecuteReader” …

With all the data inserted successfully, it’s time to find out how return all the rows. Luckily that part is straightforward. Just call the ExecuteReader method and iterate through the results.

try
{
    using (DB2Connection conn = new DB2Connection(connectionString))
    {
        conn.Open();

        using (DB2Command cmd = conn.CreateCommand())
        {
            cmd.CommandType = CommandType.Text;
            cmd.CommandText = "EXECUTE PROCEDURE customer_select()";

            var dr = cmd.ExecuteReader();
            while (dr.Read())
            {
                Console.WriteLine("customer_id: {0}, customer_name: {1}, customer_info: {2}", dr[0], dr[1], dr[2]);
            }
        }
    }
}
catch (DB2Exception exception)
{
    Console.WriteLine("Error Message: {0}", exception.Message);
}