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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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16 changes: 16 additions & 0 deletions aspnetcore/fundamentals/minimal-apis/includes/parameter-binding8-10.md
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Expand Up @@ -217,6 +217,22 @@ For more information on XSRF attacks, see [Antiforgery with Minimal APIs](xref:s

For more information, see [Form binding in Minimal APIs](https://andrewlock.net/exploring-the-dotnet-8-preview-form-binding-in-minimal-apis/);

#### IFormFile collection binding behavior

The following table summarizes how different `IFormFile` collection parameter types are bound in Minimal APIs:
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| Parameter type | Bound value | Honors parameter name? |
| --- | --- | --- |
| `IFormFileCollection` | All files in `HttpContext.Request.Form.Files` | No |
| `IFormFile` | The single file whose form field name matches the parameter name | Yes |
| `IReadOnlyList<IFormFile>` | All files whose form field name matches the parameter name | Yes |
| Other `IFormFile` collection types (`IEnumerable<IFormFile>`, `List<IFormFile>`, `IFormFile[]`, etc.) | Not supported — parameter is not populated | n/a |
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Use `IFormFileCollection` when you need all uploaded files regardless of form field name. Use `IReadOnlyList<IFormFile>` when you need only the files whose form field name matches the parameter name.

> [!NOTE]
> This same binding behavior applies to properties on `[AsParameters]` types and form-mapped complex types, since the form-mapping layer is shared with Blazor.

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## Bind to collections and complex types from forms
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