Workflows, Transitions, Conditions, Validators, and Post Functions
What to know
A workflow is a set of statuses connected by transitions. Each transition can have a condition (who may execute it), a validator (input must satisfy a rule before it proceeds), and post functions (actions after success, such as setting a field or firing an event). The workflow scheme binds workflows to issue types in a project. Global transitions apply from any status. Properties and the workflow designer help manage complex flows. Understand that conditions block visibility/execution, validators block completion, and post functions run only on success.
Traps
Questions often ask the order of execution: condition, then validator, then post function. A condition failure hides or blocks the transition; a validator failure shows an error and stops it. Post functions can update fields, but a field updated by a post function may not appear until the screen refreshes. Also, a transition without a condition is open to anyone with the transition permission. Watch for "who can transition" versus "who can edit."
Rule of thumb
Use conditions to restrict actors, validators to enforce data quality, and post functions to automate side effects. Keep post functions idempotent and test ordering when multiple post functions touch the same field.
Worked example
A transition to "Done" must require a resolution and notify the reporter. Add a validator requiring the Resolution field, then a post function that sets Resolution if empty, then a post function firing the issue-updated event. Order matters: set the field before the event fires.