fix(configdb): InstanceLocator single untracked projected join (review 2026-10-21 08/P7)

src/ZB.MOM.WW.ScadaBridge.ConfigurationDatabase/Services/InstanceLocator.cs

@@ -22,15 +22,13 @@ public class InstanceLocator : IInstanceLocator
         string instanceUniqueName,
         CancellationToken cancellationToken = default)
     {
-        var instance = await _context.Set<Commons.Entities.Instances.Instance>()
+        // One untracked projected join: this sits on the inbound-API Route.To hot path and
-            .FirstOrDefaultAsync(i => i.UniqueName == instanceUniqueName, cancellationToken);
+        // only needs a single string, so it must not materialise (and track) two entities.
-
+        return await (
-        if (instance == null)
+                from i in _context.Set<Commons.Entities.Instances.Instance>().AsNoTracking()
-            return null;
+                join s in _context.Set<Commons.Entities.Sites.Site>().AsNoTracking() on i.SiteId equals s.Id
-
+                where i.UniqueName == instanceUniqueName
-        var site = await _context.Set<Commons.Entities.Sites.Site>()
+                select s.SiteIdentifier)
-            .FindAsync(new object[] { instance.SiteId }, cancellationToken);
+            .FirstOrDefaultAsync(cancellationToken);
-
-        return site?.SiteIdentifier;
     }
 }

tests/ZB.MOM.WW.ScadaBridge.ConfigurationDatabase.Tests/RepositoryCoverageTests.cs

@@ -1486,6 +1486,24 @@ public class InstanceLocatorTests : IDisposable
         Assert.Equal("SITE-001", result);
     }
 
+    /// <summary>The lookup must not track entities (single untracked projection, review 08/P7).</summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
+    [Fact]
+    public async Task GetSiteIdForInstance_DoesNotTrackEntities()
+    {
+        var site = new Site("Site1", "SITE-001");
+        var template = new Template("T1");
+        _context.Sites.Add(site);
+        _context.Templates.Add(template);
+        await _context.SaveChangesAsync();
+        _context.Instances.Add(new Instance("Pump1") { SiteId = site.Id, TemplateId = template.Id });
+        await _context.SaveChangesAsync();
+        _context.ChangeTracker.Clear();
+
+        Assert.Equal("SITE-001", await _locator.GetSiteIdForInstanceAsync("Pump1"));
+        Assert.Empty(_context.ChangeTracker.Entries());
+    }
+
     /// <summary>Verifies that getting the site id for a missing instance returns null.</summary>
     /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]