Make a Custom File Reader

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!

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

You can useFrom URL to import the component.

Copy paste the URL from here:

git@bitbucket.org:interfaceware/file_tutorial.git

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

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.

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.

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:

A Functions
FIL Library used to get the file name
Using trace() function

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:

Writing a Functions
Using trace() function
Using APP as a prefix, to maintain a common naming convention
Custom Fields

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

IdList = IdList:split(",")

You should see something like:

Concepts used:

String:split()

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:

A Functions
# Operator on Strings to get the length of the prefix
https://interfaceware.atlassian.net/wiki/spaces/IXB/pages/2685337684
https://interfaceware.atlassian.net/wiki/spaces/IXB/pages/2685665315

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:

https://interfaceware.atlassian.net/wiki/spaces/IXB/pages/2684355428 and go to the component card for https://interfaceware.atlassian.net/wiki/spaces/IXB/pages/2650931201.

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

This means refining the APPidList function.

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

Concepts:

Add intuitive https://interfaceware.atlassian.net/wiki/spaces/IXB/pages/2684322170 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 https://interfaceware.atlassian.net/wiki/spaces/IXB/pages/2689335358 for a quick explanation on the double-dot notation.

Add https://interfaceware.atlassian.net/wiki/spaces/IXB/pages/2684485918 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.