spec: a roll-up recomputes on the child's update too - #40
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1.5 states a roll-up's event set only for the counting case, and states it as create / delete. Create and delete are not the only ways a parent's set of children changes: a child changes parents by an ordinary edit of its own parent relation, and on that reading nothing recomputes - the parent that received the child does not count it and the parent that lost it goes on counting it. The proposal makes the event set a property of the construct rather than of the aggregation: create, update and delete for every op, with the affected parent on an update being the one the child names after the edit. The keyed sibling `aggregates` has been normative on exactly this since 1.1. No new syntax.
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Proposal
0021-rollups-recompute-on-child-update.md(proposal-first —versions/untouched).1.5 states a roll-up's event set only for the counting case, and states it as create / delete:
Create and delete are not the only ways the set of children of a parent changes. A child changes parents by an ordinary edit of its own parent relation — a task dragged to another sprint, a loan reassigned to another member. No child is created and none destroyed, so on that reading nothing recomputes: the parent that received the child does not count it, the parent that lost it goes on counting it, and both stay wrong until some unrelated child of the same parent happens to be created or deleted.
The proposal makes the event set a property of the construct rather than of the aggregation — create, update and delete for every
op— with the affected parent on an update being the one the child names after the edit, and the vacated parent left to a moved-key event where a generator publishes one.aggregates, the keyed sibling, has been normative on exactly this since 1.1.No new syntax. The
Specification textsection carries the replacement opening sentence and the new normative paragraph, at therollupsanchor.Implementation: eclipse-dirigible/dirigible#6820.
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