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Saturday, 18 April 2020

Documenting from the metadata source with a Salesforce CLI Plug-In - Part 3


Introduction

In Part 1 of this series, I explained how to generate a plugin and clone the example command. In Part 2 I covered finding and loading the package.json manifest and my custom configuration file

In this instalment, I'll show how to load and process source format metadata files - a key requirement when documenting from the metadata source, I'm sure you'll agree.

Walking Directories

In order to process the metadata files, I have to be able to find and iterate them. As I'm processing object files, I also need to process the fields subdirectory that contains the metadata for the custom fields that I'm including in my document. I'll use a number of standard functions provided by Node in order to achieve this.

I know the top level folder name for the source format data, as it is the parameter of the -s (--source-dir) switch passed to my plugin command. To simplify the sample code, I'm pretending I know that the custom objects are in the objects subfolder, which isn't a bad guess, but in the actual code this information is pulled from the configuration file. To generate the combined full pathname, I use the standard path.join function, as this figures out which operating system I'm running on and uses the correct separator:

import { join } from 'path';
...
let objSourceDir=join(sourceDir, 'objects');
I then check that this path exists and is indeed a directory - this time while I use the standard fs.lstatSync to check the path is a directory, I use a homegrown function to check that the path exists: 

import { lstatSync} from 'fs';
import { fileExists } from '../../shared/files';
 ...
if ( (fileExists(objSourceDir)) && 
     (lstatSync(objSourceDir).isDirectory()) ) {

Once I know the path is there and is a directory, I can read the contents, again using a standard function - fs.readdirSync - and iterate them :

let entries=readdirSync(objSourceDir);
import { appendFileSync, mkdirSync, readdirSync } from 'fs';
  ...
for (let idx=0, len=entries.length; idx<len; idx++) {
    let entry=entries[idx];
    let entryPath=join(objSourceDir, entries[idx]);
}

Reading Metadata

The Salesforce metadata is stored as XML format files, which presents a slight challenge when working in JavaScript. I can use the DOM parser, but I find the code that I end up writing looks quite ugly, with lots of chained functions. My preferred solution is to parse the XML into a JavaScript object using a third party tool - there are a few of these around, but my current favourite is fast-xml-parser because

  • it's fast (clue is in the name)
  • it's synchronous - this isn't a huge deal when writing a CLI plugin, as the commands are async and can thus await asynchronous functions, but when I'm working with the command line I tend towards synchronous
  • it's popular - 140k downloads this week
  • it's MIT licensed
It's also incredibly easy to use. After installing by running npm install --save, I just need to import the parse function, load the XML format file into a string and parse it!

import { parse} from 'fast-xml-parser';

let objFileBody=readFileSync(
join(entryPath, entry + '.object-meta.xml'), 
                  'utf-8');
let customObject=parse(objFileBody);

My customObject variable now contains a JavaScript object representation of the XML file, so I can access the XML elements as properties:

let label=customObject.CustomObject.label;
let description==customObject.CustomObject.description;

Which allows me to extract the various properties that I am interested in for my document.

In the next exciting episode I'll show how to enrich the objects by pulling in additional information from other files.

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