Phase 1 of the design at
docs/plans/2026-05-12-derive-on-compose-design.md.
Additive schema only — no behavior changes. Existing data and code
paths continue to work; subsequent phases will start writing the
new fields.
Template gains:
IsDerived true when this row was auto-created to back
a composition slot
OwnerCompositionId back-ref to the owning TemplateComposition
(plain int, not an EF nav property — managed
by TemplateService for cascade-delete)
TemplateAttribute / TemplateScript each gain:
IsInherited row copied from base and not yet overridden;
changes to the base flow downward
LockedInDerived on a base, blocks derived from overriding;
enforced at the service layer in later phases
EF Core migration AddDerivedTemplateFields adds four columns:
Templates.IsDerived bit NOT NULL DEFAULT 0
Templates.OwnerCompositionId int NULL
TemplateAttributes.IsInherited bit NOT NULL DEFAULT 0
TemplateAttributes.LockedInDerived bit NOT NULL DEFAULT 0
TemplateScripts.IsInherited bit NOT NULL DEFAULT 0
TemplateScripts.LockedInDerived bit NOT NULL DEFAULT 0
Existing rows get the defaults. Tests across SiteRuntime / TemplateEngine
/ CentralUI suites stay green (129 / 199 / 159).
Next: phase 2 — wire AddCompositionAsync to derive on compose for
new compositions. Old data still flows the direct-reference path
until phase 3's migration script.
5615f3d0c7