====== Use Case: Write to disk depending on partnervariables ======

In this HowTo, you will learn which conditions are necessary for implementing your own plug-in. Below you can follow the implementation on the basis of a use case, be written in the attachments of a message to the hard disk, if the partner has filed a corresponding variable (with a path).

==== Create the Jobstep class ====

To do this, first create a new project in Visual Studio with the settings:
  * **Target framework**: minimum **.NET Framework 4.5** or higher
  * **Project reference**: the **eBiss.Api** .dll, which can be found in your ebiss directory. 
  * 
You can find the complete project in your eBiss standard templates subdirectory, at:
\StandardTemplates\PluginSample\eBiss.Plugin.Sample

Let's first create our Jobstep with the name AttachmentWriter. For this, our created class inherits from an abstract class ** ClientJobStepBase ** and implements the Run () method. We also need private methods that read a partnervariable and write the attachment to the hard disk using a stream.


<code csharp>
public class AttachmentWriter : ClientJobStepBase
{
    #region Internal and private Member

    private void WriteToFile(IAttachment attachment, string folder)
    {
        using (Stream readStream = attachment.OpenReadStream())
        {
            string outFn = attachment.Filename;
            if (String.IsNullOrEmpty(outFn))
            {
                outFn = attachment.Oid + ".dat";
            }

            if (folder[folder.Length - 1] != '/' && folder[folder.Length - 1] != '\\')
            {
                folder += "\\";
            }

            string fn = folder + outFn;
            LogContext.Debug("Write attachment to file: " + fn);

            using (Stream writeStream = File.Create(fn))
            {
                byte[] fileBuff = new byte[1024];

                int bytesRead = 0;
                while ((bytesRead = readStream.Read(fileBuff, 0, fileBuff.Length)) > 0)
                {
                    writeStream.Write(fileBuff, 0, bytesRead);
                }

                writeStream.Flush();
                writeStream.Close();
            }
        }
    }

    private bool CheckVariableForWriteAttachment(IPartner partner)
    {
        ILocation loc = partner.MainLocation;
        IVariableInstance writeAttachment = loc.VariableInstances.Where(v => v.VariableDefinition.Name == "WriteAttachment").FirstOrDefault();

        if (writeAttachment != null)
            return writeAttachment.Value_Bool;

        return false;
    }

    private string GetPath(IPartner partner)
    {
        ILocation loc = partner.MainLocation;
        IVariableInstance writeAttachmentPath = loc.VariableInstances.Where(v => v.VariableDefinition.Name == "AttachmentPath").FirstOrDefault();

        if (writeAttachmentPath != null && string.IsNullOrWhiteSpace(writeAttachmentPath.Value_Text) == false)
        {
            string outPath = writeAttachmentPath.Value_Text;
            if (!Directory.Exists(outPath))
            {
                throw new ApplicationException($"Path '{outPath}' from variable AttachmentPath for partner '{partner.Name}' is not a valid or existing directory.");
            }
            return outPath;
        }

        return null;
    }
[...]
</code>

The Run method is then implemented and, in our case, logged sufficiently using our LogContext. Effectively iterating through a list of messages and checks whether the current partner has a variable called "Write Attachment". Then the variable "AttachmentPath" validates the corresponding path and writes the attachment to the disk using a stream. In case of error, we throw an exception and assign a task.

<code csharp>
public override JobStepResult Run()
{
    JobStepResult rc = JobStepResult.Ok;

    LogContext.Debug("Enter");
    foreach (IMessage msg in Job.InputMessages)
    {
        try
        {
            if (CheckVariableForWriteAttachment(msg.Partner) == false)
            {
                LogContext.Debug($"Variable 'WriteAttachment' not set or false for Partner '{msg.Partner.Name}'.");
            }
            else
            {
                string folder = GetPath(msg.Partner);

                if (folder != null)
                {
                    foreach (IAttachment attachment in msg.Attachments)
                    {
                        WriteToFile(attachment, folder);
                    }
                }
                else
                {
                    throw new ApplicationException($"Variable 'AttachmentPath' for Partner '{msg.Partner.Name}' is not set.");
                }
            }
        }
        catch (Exception ex)
        {
            LogContext.Exception(ex);

            this.Job.AddTask(msg, ex.Message);

            rc = JobStepResult.Error;
        }
    }
    LogContext.Debug("Exit with: " + rc.ToString());
    return rc;
}
</code>


Create your project and copy the .dll to the eBiss Plugin subdirectory. Once you have restarted the service, you will find your jobsteps in the Workflow Editor.

{{:howtos:plugins:jobsteps:jobexampletwo.png?nolink&500|}}

//Fig. 1: Jobstep in the Workflow-Editor//