Often, during the development of an integration or a special customization, people get stuck because of the lack of context. Questions appear: which user pressed on the next status button? 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, 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 a rather bad 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 will figure out what it means and how it can simplify your SIL 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.
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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, and will load that particular value, and start from there. The flag will therefore flip be flipped and the counter will be incremented with each executed transition on that issue.
What's more is that if If you move to another issue and execute the same post function multiple time, 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.
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- linked to the current issue from the context,
- its initializer is just executed first time (no matter the right expression, the right expression is totally ignored)
- a variable whose value survives the script, making it available in some other scripts under the same name
Usage Outside the Issue Context
The usage outside the issue context is the same. However, due to the nature of the persistent keyword, the variable becomes a global variable. Take for instance the following script, run from the SIL Runner gadget:
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| Info |
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Persistent variables are effectively global if used outside of the issue context. |
Helper Routines
Two helper routines are available to deal with persistent vars:
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| Code Block |
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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.
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