[Ketan vijayvargiya (ketanvijayvargiya)]

Changes proposed in this pull request

• DriveItemRequestBuilderExtensions finds the request builder's backing fields (request adapter, path parameters, URL template) with GetType().BaseType.GetFields(NonPublic | Instance).FirstOrDefault(...). That scan ran on every call of GetRequestAdapter, GetPathParameters, GetUrlTemplate and UpdateUrlTemplate, so every ItemWithPath(...) and every property read on CustomDriveItemItemRequestBuilder repeated it.
• The FieldInfo is now looked up once per (builder base type, field type) and kept in a static ConcurrentDictionary. The four helpers call one shared GetBackingField method; the rest of their logic is unchanged (same field is picked, same null handling).
• Only src/Microsoft.Graph/Extensions/DriveItemRequestBuilderExtensions.cs is touched. No generated code and no public API change.

Benchmark

To be upfront: the end-to-end gain is small. Building the request builder chain is dominated by other work (ToGetRequestInformation, UriBuilder, string handling), so caching the field lookup removes only a slice of it.

BenchmarkDotNet 0.15.2, [MemoryDiagnoser], .NET 10.0.14, x64, Windows 11, Release build of Microsoft.Graph (net10.0) before and after this commit.

_client = new GraphServiceClient(new AnonymousAuthenticationProvider());

[Benchmark]
public object ItemWithPathContent() => _client.Drives["d"].Root.ItemWithPath("a/b/c").Content;

Version	Run	Mean	StdDev	Allocated
Before (main)	1	2.009 us	0.103 us	6.36 KB
After (this PR)	1	1.920 us	0.031 us	6.17 KB
Before (main)	2	2.024 us	0.032 us	6.36 KB
After (this PR)	2	1.911 us	0.025 us	6.17 KB

Roughly 5% less time and 3% less allocation (about 190 bytes) per call. The time difference is close to the noise of a single run; the allocation difference is the same in every run.

Testing

• dotnet build Microsoft.Graph.sln -c Release: succeeded, 0 errors, all target frameworks (netstandard2.0, netstandard2.1, net8.0, net10.0).
• dotnet test tests/Microsoft.Graph.DotnetCore.Test -c Release --filter "FullyQualifiedName!~Functional": 96 passed, 0 failed, 0 skipped on net8.0 and on net10.0. This includes the existing DriveItemRequestBuilderExtensionsTests. The Functional tests were not run because they need a live tenant.
• No tests were added or changed.

Microsoft Reviewers: Open in CodeFlow

[Copilot]

🟢 Approval recommended

No active review issues block approval of the backing-field lookup caching change.

No open issues 🎉

What changed in this PR

This PR reduces repeated reflection work in drive-item request builders by caching backing-field lookups. It changes no generated code or public API signatures.

Changes:

• Adds a thread-safe cache keyed by builder base type and field type.
• Routes all four backing-field helpers through the shared lookup method while retaining their existing field access logic.

File	Description
src/​Microsoft.Graph/​Extensions/​DriveItemRequestBuilderExtensions.cs	Caches reflection metadata to reduce repeated field scans and allocations.

_{Review effort: Balanced}

[Ketan vijayvargiya (ketanvijayvargiya)]

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