SharePoint Attachments
Item-level attachments, built into every SP list, no column to add. Two-phase write.
Attachments are SharePoint's built-in per-item file attachment mechanism. Every SP list has them by default (unless explicitly disabled); they don't show up as a column. Binds to the Attachments field.
Write shape
Attachments are written via the per-item endpoint:
POST /web/lists/getByTitle('Orders')/items(itemId)/AttachmentFiles/add(FileName='invoice.pdf')
…with the raw file body as the request body. One call per file.
This is a post-save operation, the item must exist first to get an id.
Edge cases
- Deleting attachments, Removing an attachment from the form's value during edit triggers an explicit DELETE on the attachment URL.
- Filename collisions, SP doesn't auto-rename; uploading two files with the same name silently overwrites. The form prefixes with a UUID to avoid this.
- Disabling attachments on a list, If the list has attachments disabled (rare), the form shows a clear error rather than silently dropping the upload.
Related
Related articles
- SharePoint Image column
Modern Image column type. Two-phase write, item first, image upload in post-save.
- Attachments field
Upload files attached to the SharePoint list item, and print attached photos as pictures in the PDF report.
- Save flow, what happens when the user clicks Submit
The two-phase save pipeline, validation, primary write, then post-save writers for attachments, signatures, images, and child rows.