fix(external-system-gateway): resolve ExternalSystemGateway-011 — name-keyed repository lookups replace fetch-all-then-filter on the call hot path
This commit is contained in:
Joseph Doherty
@@ -8,7 +8,7 @@
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| Last reviewed | 2026-05-16 |
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| Reviewer | claude-agent |
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| Commit reviewed | `9c60592` |
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| Open findings | 1 |
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| Open findings | 0 |
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## Summary
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@@ -533,7 +533,7 @@ exception propagates; it was verified to fail before the `try/catch` was added.
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|--|--|
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| Severity | Low |
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| Category | Performance & resource management |
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| Status | Open |
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| Status | Resolved |
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| Location | `src/ScadaLink.ExternalSystemGateway/ExternalSystemClient.cs:360-374`, `src/ScadaLink.ExternalSystemGateway/DatabaseGateway.cs:169-176` |
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**Description**
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@@ -554,26 +554,67 @@ rather than fetch-all-then-filter.
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**Resolution**
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2026-05-16 — **Root cause confirmed, but left Open: no correct fix is possible within
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this module's edit scope.** `ResolveSystemAndMethodAsync`
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(`ExternalSystemClient.cs:360`) does call `GetAllExternalSystemsAsync()` followed by
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`GetMethodsByExternalSystemIdAsync()` and filters in memory, and
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`ResolveConnectionAsync` (`DatabaseGateway.cs:169`) does `GetAllDatabaseConnectionsAsync()`
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then filters — fetch-all-then-filter on every hot-path call, as described.
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Resolved 2026-05-16 (commit `<pending>`). A cross-module change was explicitly
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authorized, so the **name-keyed repository lookup** recommendation was applied — the
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cleaner of the two options, and one that avoids the staleness hazard a
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deployment-invalidated cache would introduce.
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Both recommended fixes require changes outside `src/ScadaLink.ExternalSystemGateway`:
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(a) a **name-keyed repository lookup** (e.g. `GetExternalSystemByNameAsync`) means adding
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methods to `IExternalSystemRepository` in `ScadaLink.Commons` and implementing them in
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`ScadaLink.ConfigurationDatabase` / `ScadaLink.SiteRuntime`; (b) an **in-memory cache
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invalidated on artifact deployment** requires subscribing to a deployment-applied event
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owned by `ScadaLink.SiteRuntime` / `ScadaLink.DeploymentManager`. A purely module-local
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cache with a time-based TTL was rejected as a fix: definitions only change on deployment
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and must reflect a deployment promptly, so a TTL would either be too short to help the
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hot path or long enough to serve stale definitions after a redeploy — trading a
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correctness hazard for a performance gain on a Low-severity issue. **Tracked follow-up:**
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add a name-keyed lookup to `IExternalSystemRepository` (Commons) and have the gateway use
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it, or add a deployment-invalidated definition cache wired from SiteRuntime. No source
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change was made in this module.
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Three name-keyed methods were added to `IExternalSystemRepository`
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(`ScadaLink.Commons`): `GetExternalSystemByNameAsync(name)`,
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`GetMethodByNameAsync(externalSystemId, methodName)` and
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`GetDatabaseConnectionByNameAsync(name)`. The connection lookup belongs on the same
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interface because database connection definitions are already part of
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`IExternalSystemRepository` (alongside `GetAllDatabaseConnectionsAsync` /
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`GetDatabaseConnectionByIdAsync`), so the existing repository organization was
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followed rather than introducing a new interface.
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Both implementers of the interface were updated:
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- `ScadaLink.ConfigurationDatabase.ExternalSystemRepository` — all three are genuine
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server-side keyed queries (`FirstOrDefaultAsync(x => x.Name == name)`, the
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method lookup additionally scoped by `ExternalSystemDefinitionId`), matching the
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existing `GetMethodByNameAsync` / `GetListByNameAsync` / `GetSharedScriptByNameAsync`
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convention in the other Central repositories.
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- `ScadaLink.SiteRuntime.SiteExternalSystemRepository` — `GetExternalSystemByNameAsync`
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and `GetDatabaseConnectionByNameAsync` are genuine single-row indexed SQLite queries
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(`WHERE name = @name`; both tables have `name` as the PRIMARY KEY).
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`GetMethodByNameAsync` resolves the named method from the parent system's
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`method_definitions` JSON column; this still requires resolving the parent system
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(one id→name scan), but the gateway's new call sequence performs **one** scan instead
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of the previous **two** (`GetAllExternalSystemsAsync` + `GetMethodsByExternalSystemIdAsync`,
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which itself scanned), so the site path is strictly better than before — noted as
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the one place a residual scan remains, bounded by the deployed system count.
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`ExternalSystemClient.ResolveSystemAndMethodAsync` and
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`DatabaseGateway.ResolveConnectionAsync` were rewritten to call the keyed lookups; the
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`GetAllExternalSystemsAsync` / `GetMethodsByExternalSystemIdAsync` /
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`GetAllDatabaseConnectionsAsync` + in-memory `FirstOrDefault` filtering is gone from
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both hot paths.
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Regression tests (TDD — written first, verified failing/not-compiling before the
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implementation, then confirmed green; one was additionally verified to fail when the
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keyed query is deliberately broken):
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- ConfigurationDatabase (`RepositoryCoverageTests`):
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`GetExternalSystemByName_ReturnsMatchingRow`,
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`GetExternalSystemByName_MissingName_ReturnsNull`,
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`GetMethodByName_ReturnsMethodScopedToParentSystem`,
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`GetMethodByName_MissingMethod_ReturnsNull`,
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`GetDatabaseConnectionByName_ReturnsMatchingRow`,
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`GetDatabaseConnectionByName_MissingName_ReturnsNull`.
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- SiteRuntime (`SiteRepositoryTests`):
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`ExternalSystemRepository_GetByName_ReturnsMatchingDefinition`,
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`ExternalSystemRepository_GetByName_MissingName_ReturnsNull`,
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`ExternalSystemRepository_GetMethodByName_ResolvesScopedToSystem`,
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`DatabaseConnectionRepository_GetByName_ReturnsMatchingDefinition`.
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- ExternalSystemGateway: the existing `ExternalSystemClientTests` /
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`DatabaseGatewayTests` resolution stubs were migrated to the keyed methods (via
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`StubResolution` / `StubConnection` helpers), so the full gateway suite now exercises
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and protects the keyed-lookup resolution path.
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`dotnet build ScadaLink.slnx` is clean; `ScadaLink.ExternalSystemGateway.Tests` (54),
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`ScadaLink.ConfigurationDatabase.Tests` (106), `ScadaLink.SiteRuntime.Tests` (196) and
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`ScadaLink.Commons.Tests` (226) all pass.
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### ExternalSystemGateway-012 — Permanent-failure logging requirement is not met; `_logger` is injected but unused
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