Saturday, 31 March 2018

Building My Own Learning System - Part 6

Building My Own Learning System - Part 6

Versions

Introduction

In previous posts in this series I covered the initial idea and development through to sharing the code with installation, configuration etc instructions. Now that I have the basics working I’ve started to iterate and add a few features. Oddly the first feature I added was the one that I most recently thought of - the ability to display a custom message to the user when they complete a path, retrieved from the path itself. I’m thinking that this will allow me to carry use the system for more interesting challenges - complete a path to get a keyword, or a location, something like that anyway,. I did say I’d just thought of it, not that I’d thought it through!  It was only a few lines of code to implement this, just a change to the PassStep method so that it returned a tuple of a completed state and message to display, A few tweaks to the unit tests and I carried out an sfdx deployment to my sample endpoint and verified with my updated client code that all was working as expected and my sample Bob Buzzard character path was displaying the custom message:

Screen Shot 2018 03 31 at 16 14 48

Then it hit me - anyone that didn’t have my new client would get errors when accessing the sample endpoint, and they’d have to dig into the debug logs to figure out why. Suddenly it was important to add another feature. (Looking at my sample endpoint it appears that there’s only me using it at the moment anyway, so I guess if you are going to break things then the earlier the better!).

Versioning

Like most things in the tech world, there are loads of different ways to handle versioning. I considered the Salesforce route of having different endpoints for each version and discounted it. I’m not convinced that I want to be supporting older versions and I don’t particularly want to get into managing a number of classes representing historic versions. Salesforce can do this because they have more than one person maintaining things in their downtime, and if I ever become a multi-billion dollar company I’ll reconsider.

The route I ended up going was defining the version for each of the client and server in code, and having the client send its version with every request to an endpoint. The endpoint then compares this to its version and decides if it can handle the request. This gives me the option of supporting older versions if I want to, without committing me to any level of service! If the endpoint can't handle the request it throws an exception indicating what needs to happen - either upgrade the client or ask the admin of the endpoint to upgrade that. The updated client displays the error message to the user who can jump on any required action.

Installing the Latest ... Version

The current version of the system is now V1.0, and I’ve created github releases for both the endpoint and client, both of which have been tagged as V1.0. 

The unmanaged package the client V1.0 release is : <Salesforce instance>/packaging/installPackage.apexp?p0=04t0O000001IqIm

Related Information

As I plan to continue with these posts as I add new features or learn that I’ve made a terrible mistake should have done things differently, I’ve moved the list of posts into a dedicated page on this blog. 

 

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