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Document IFormFileCollection vs IReadOnlyList<IFormFile> binding behavior in Minimal APIs#37180

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Document IFormFileCollection vs IReadOnlyList<IFormFile> binding behavior in Minimal APIs#37180
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Copilot AI commented May 21, 2026 •
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Fixes #37173

Minimal API form-file binding has undocumented behavioral differences depending on parameter type — IFormFileCollection ignores the parameter name and binds all files, IReadOnlyList<IFormFile> binds only name-matched files, and other collection types silently don't bind at all. Requested by framework team in dotnet/aspnetcore#66757.

Changes:

  • Added #### IFormFile collection binding behavior subsection to parameter-binding8-10.md after the existing form-file binding content
  • Added comparison table covering IFormFileCollection, IFormFile, IReadOnlyList<IFormFile>, and unsupported collection types
  • Added note that the same behavior applies to [AsParameters] and form-mapped complex types (shared form-mapping layer with Blazor)
Parameter type Bound value Honors parameter name?
IFormFileCollection All files in HttpContext.Request.Form.Files No
IFormFile Single file matching parameter name Yes
IReadOnlyList<IFormFile> All files matching parameter name Yes
Other collection types Not supported n/a

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aspnetcore/fundamentals/minimal-apis/parameter-binding.md aspnetcore/fundamentals/minimal-apis/parameter-binding

Copilot AI linked an issue May 21, 2026 that may be closed by this pull request
Document IFormFileCollection vs IReadOnlyList<IFormFile> binding behavior in Minimal APIs #37173
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Copilot AI changed the title [WIP] Document IFormFileCollection vs IReadOnlyList<IFormFile> binding behavior Document IFormFileCollection vs IReadOnlyList<IFormFile> binding behavior in Minimal APIs May 21, 2026
Copilot AI requested a review from wadepickett May 21, 2026 20:45
@wadepickett wadepickett requested a review from Copilot May 21, 2026 20:51
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Pull request overview

Documents the (previously undocumented) differences in Minimal API form-file binding behavior across IFormFile-related parameter types, helping readers choose the correct type for “all files” vs “name-matched files” scenarios.

Changes:

  • Added an “IFormFile collection binding behavior” subsection under the existing form binding section.
  • Added a comparison table describing binding results for IFormFileCollection, IFormFile, IReadOnlyList<IFormFile>, and unsupported collection shapes.
  • Added a note that the same behavior applies for [AsParameters] and form-mapped complex types.

Comment thread aspnetcore/fundamentals/minimal-apis/includes/parameter-binding8-10.md Outdated
Comment thread aspnetcore/fundamentals/minimal-apis/includes/parameter-binding8-10.md Outdated
wadepickett and others added 2 commits May 21, 2026 13:57
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Potential fix for pull request finding
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Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
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Potential fix for pull request finding
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Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
@wadepickett wadepickett marked this pull request as ready for review May 21, 2026 20:58
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wadepickett reviewed May 22, 2026
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Comment thread aspnetcore/fundamentals/minimal-apis/includes/parameter-binding8-10.md Outdated
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wadepickett approved these changes May 22, 2026
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Approved after a few fixes have now been addressed.

@wadepickett wadepickett requested a review from tdykstra May 22, 2026 19:54
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wadepickett commented May 22, 2026 •
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@danroth27, Internal review link directly to the new section for your review on this binding behaviour update.

@wadepickett wadepickett requested a review from danroth27 May 22, 2026 20:04
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wadepickett commented May 22, 2026

@copilot, also update the file that uses this include to have the latest ms.date value in the metadata:
dotnet/AspNetCore.Docs/refs/heads/main/aspnetcore/fundamentals/minimal-apis/parameter-binding.md

update this:
ms.date: 10/22/2025

to this:
ms.date: 05/22/2026

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Copilot AI commented May 22, 2026

@copilot, also update the file that uses this include to have the latest ms.date value in the metadata:
dotnet/AspNetCore.Docs/refs/heads/main/aspnetcore/fundamentals/minimal-apis/parameter-binding.m...

Updated ms.date to 05/22/2026 in aspnetcore/fundamentals/minimal-apis/parameter-binding.md.

Copilot AI requested a review from wadepickett May 22, 2026 20:16
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wadepickett approved these changes May 22, 2026
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Approved, after a few updates were applied.

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Document IFormFileCollection vs IReadOnlyList<IFormFile> binding behavior in Minimal APIs

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