Persistent variables

Often, during the development of an integration or a special customization, people get stuck because of the lack of context. Questions appear: which user clicked the button for the next status? Did the manager approve this item? What was the result of the calculation in the previous step? The traditional way of dealing with such questions was to create additional custom fields to keep that data, usually hidden from users (so excluded from the screens schemes), effectively adding bloat to Jira and ultimately worsening indexing - and general - performance. To help you answer these kinds of questions, Simple Issue Language™ (or SIL™) acquired, starting with version 4.1.7 of the SIL Engine™, a new feature, called persistent variables.

So, what's a persistent variable? In short, in an issue context, a persistent variable is a value inherently linked to the issue. Think of it as an extension of the issue fields, or - making another analogy - an additional custom field, but internal to SIL™. Outside the issue context, the persistent variable becomes a global variable, accessible from all scripts. It is better to see some usage, so you can get a better grasp on what it means and how it can simplify your SIL™ usage throughout your Jira integration.

Usage in an issue context

Persistent variables are introduced via the persistent keyword. In order to save space, we do not allow persistent and constant modifiers to be used on the same variable, so you can't have both. A persistent variable is always modifiable.

Let's install the following post function on an easy executable action (like "Start Progress" on the default simplified workflow of Jira), and execute the transition a number of times (a normal Start-Stop progress cycle, in this example, on the same issue).

persistent number counter = 1; 
persistent boolean flag = false; 
 
description += "\n" + counter + "(" + flag + ")"; 
 
flag = !flag; 
 
counter ++;

The above example adds some text to the description of an issue, but unlike the version without the persistent keyword, the appended text will be something like:

1(false)
2(true)
3(false)
4(true)

So what's happening here? The truth is that the initialization of the variable happens only once. Subsequent executions will find the persistent variable initialized, will load that particular value, and start from there. The flag will be flipped, and the counter will be incremented with each executed transition on that issue.

If you move to another issue and execute the same post function multiple times, you will get a similar output. The first line of the output will still be 1(false) followed by 2(true) and so on, which means that the persistent variable is linked to that issue.

Let's suppose that we have a SIL™ listener and we'd like to use that counter variable. You can simply access it in your listener like in the following example:

persistent number counter;
persistent boolean flag = true; //initialization is ignored if the previous script was already executed!
//.............
/// use it in the listener like a normal variable:
counter--;

Note that we didn't put any initializer. If the variable is already initialized, the initializer is simply not executed at all, no matter the construct. While such behavior belongs to the logic of the persistent variable, you might find this rather strange and sometimes prone to errors. We recommend that you use the same initializer every time (maybe a constant?) so that you won't start with different values.

In conclusion:

1. Persistent variable is linked to the current issue from the context.
2. Its initializer is executed just the first time (no matter the right expression, the right expression is utterly ignored).
3. A persistent variable is a variable whose value survives the script, making it available in many other scripts under the same name.

Usage outside the issue context

The usage outside the issue context is very similar. However, due to the nature of the persistent keyword, the variable in this case becomes a global variable. Take for instance the following script, run from the SIL™ Runner gadget:

persistent number counter = 1; 
persistent boolean flag = false; 
 
TEST-1.description += "\n" + counter + "(" + flag + ")"; 
 
flag = !flag; 
 
counter ++;

The counter variable will be incremented as before (starting from 1) and the text above will be re-appended to the issue 'TEST-1'. However, if we change just the issue, say to 'TEST-2', the counter will retain its previous value, incrementing from the value it stopped when you run the above for the TEST-1 issue. Just try it!

Helper routines

We made two helper routines available to ease your work with persistent variables:

Values are treated as strings. For the above example:

string globalCounterVar = getPersistentVar("counter");
number test_one_counter = getPersistentVar("TEST-1", "counter"); //notice the implicit cast! values are treated like strings, though!

Notes

• Although useful, persistent variables come with a small performance penalty. Don't overuse them!
• There's no way to delete a persistent var (other than direct SQL) at the moment. Think hard if you really need them.