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This is good example of how we can usePrefix Namespaces for Separating Concerns by building a custom file reader component which has a simple interface for a unique purpose rather than using a general purpose no code solution - see The problem with no-code solutions.

Here’s a scenario:

A large lab needs to have a file reading component which can feed files from different customers based on the prefix of the file, i.e. some files start with JJ99, others XYZ etc. depending on the source.

Let’s do it!

 Use +FROM URL to import a custom version of the file reader component for this tutorial

This component generates some test files to make it easier to learn how to make a custom file reader.

You can useCreate component +FROM URL to import the component.

Copy paste the URL from here:

git@bitbucket.org:interfaceware/file_tutorial.git
 Click Edit on the component card, then MAKE A COPY AND EDIT to open the Translator editor

Refer to Edit a Component to see how it's done if you have not done this before.

 Examine the Custom Field configurations in the component in config.json

To simplify the tutorial we have set these up a ClientList with the filename prefix Ids. Click on the config.json and you should see:

See Custom Fields to understand how this was created.

 Click on MatchRules.lua in the Project Tree to see where we need to alter the code

Navigate to MatchRules.lua in the Project Tree. This is the function we need to alter:

function MatchFile(FileName)
   return true
end

The file reader component is deliberately simple and uses separation of concerns to make it more obvious how to modify the code to meet new needs. We need this function to return true when the matching criteria are met.

 Let's extract the filename using FILfilename() from the FIL Library, so we can look at it:

Change the matching to add in two lines so we can see the filenames we need to filter on.

function MatchFile(FileName)
   local JustFileName = FILfilename(FileName)
   trace(JustFileName)
   return true
end

These are the concepts we have used:

 Edit MatchRules.lua to extract the prefixes from the custom fields

Create a second function, APPidList, to extract the ClientList prefixes from the custom fields and update MatchFile to call APPidList.

You can replace the contents of the MatchRules.lua file with this new code:

function APPidList()
   local IdList = component.fields()["ClientList"]
   return IdList
end

function MatchFile(FileName)
   local IdList = APPidList()
   trace(IdList)
   local JustFileName = FILfilename(FileName)
   trace(JustFileName)
   return true
end

Concepts used:

 Break the comma delimited string into a list to get each prefix Id

We can quickly do this by adding one line to AppidList after line 2:

IdList = IdList:split(",")

You should see something like:

Concepts used:

 Make a matching function which takes the prefix and sees if the filename starts with it

Create a third function, APPmatchPrefix, to determine if the filename matches the prefix. You can copy the code below: 

function APPmatchPrefix(Prefix, FileName)
   local Part = FileName:sub(1, #Prefix)
   trace(Part, Prefix)
   return (Part == Prefix)
end

See the screenshot below and add a line to MatchFile to call and invoke AppmatchPrefix.

Concepts used:

 Now change the matching code in MatchFile() so we iterate through the prefix list

Let’s modify the code to go through the entire list of prefixes:

for i = 1, #IdList do
   if APPmatchPrefix(IdList[i], JustFileName) then 
      return true
   end
end
return false -- we didn't match anything

And this is what you should see:

Concepts used:

 Commit your changes, alter the component to run on the new commit, and run it!

Commit and Push Changes to Git and go to the component card for Choosing the code to run for your component.

You’re done! The next steps are how you could further refine the code

 Make the configuration more robust by trimming the white space from the list of prefixes

This means refining the APPidList function.

That would involve looping through the list and removing white space from each ID:

Concepts:

 Customize the logging using iguana.log*

Add intuitive Custom Logging for your component to increase visibility into processing and adding meaningful messages to help with troubleshooting.

You can see an example of this in main.lua on line 25:

iguana.log("Polling every "..Polltime.." seconds");

Try it for yourself!

See Concatenating strings for a quick explanation on the double-dot notation.

 Customize the status using component.setStatus{data="Text"}

Add Custom Status for your component to have it display real time updates at the bottom of the component card as its running.

This component already creates custom status on lines 31-36 of main.lua.

Try it for yourself!

There is no limit to how you can streamline the usage of a custom component - if that helps address a bottleneck, then it is well worth it.  

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