Form attachment to SharePoint column field using SharePoint HTTP Patch

[F_Quint]

Hi, 

I got a flow where I get response details from a Form. One of the options in the form is the ability to upload a file. 

This file is usually an image (Jpeg).  I'm parsing the response details for this option in the form. Then I'm adding these to the SharePoint HTTP Patch JSON step.

The column I want to upload these files to is called "screenshot", when running this I get the following error

An entry without a type name was found, but no expected type was specified. To allow entries without type information, the expected type must also be specified when the model is specified. 

[v-bacao-msft · Accepted solution]

Hi @F_Quint ,

If you want to upload the file uploaded in the Form submission as an item attachment, you can refer to this video below:

https://www.youtube.com/watch?v=Foy8i6jPZrg

Best Regards,

[HEATFreight]

THIS. IS. NOT. A. SOLUTION!

This post clearly requested a solution "using SharePoint HTTP Patch", whereas the solution you have linked to uses "Add Attachment" instead of "Send an HTTP Request to SharePoint".

But the "Add Attachment" action only supports one file and it is not capable of overwriting conflicts!

This is a bad solution. If you have multiple files, you must use an "Apply to each" loop to encapsulate the "Add Attachment" action, but not only that, you must also run an "Apply to each" loop beforehand to delete all attachments with conflicting file names! Not good...

See my reply to a similar thread, copied below:

I found a tutorial to batch delete attachments to a SharePoint list item here but have had trouble finding an example of how to "Send an HTTP Request to SharePoint" to batch upload files to a SharePoint list item. NOT TO A DOCUMENT LIBRARY OR FOLDER, BUT SPECIFICALLY TO A LIST ITEM...

It seems there should be a way to batch multiple attachments into one REST API request and have those all upload and overwrite any existing duplicates of the same file names, all in one request and without using a preliminary DELETE request (like the example linked above) to avoid conflicts.

I can't even find an example HTTP request to upload attachments, specifically, to a list item. I can use the "Add Attachment" action in Power Automate, and obviously that works fine, but it requires, first, an "Apply to each" loop to delete all existing file conflicts (any file with a name matching one you intend to upload) followed by another "Apply to each" to run the "Add Attachment" action for each file. And you can't have these request running in parallel because they would interfere with each other.

So the crux of the problem is we need to upload all the desired attachments in one batch request that overwrites all conflicting file names! This has to be possible, I just haven't found any examples...

Link to tutorial for SharePoint HTTP Batch Delete attachments from SharePoint list item

EDIT: Well crap... According to this documentation, it's actually not possible to upload multiple files to SharePoint API via a single batch. However, this other documentation explains how to structure SharePoint HTTP requests to upload/delete/modify files attached to a SharePoint list item, which may be preferable to the above mentioned DELETE-then-UPLOAD method. Even if only one file per "batch" is allowed, if the HTTP request can overwrite conflicting files without first deleting, then it obviates one whole SharePoint request per file and eliminates the entire "Apply to each" loop to delete the conflicts.

[HEATFreight]

Here is the solution:

/_api/web/getfolderbyserverrelativeurl('Lists/List1/Attachments/1/')/files/add(overwrite=true,url='filename.txt')

The answer is also found here, but they do not go into how lists are also folders and how to access list items as folders. The above syntax makes it easy to understand.

[HEATFreight]

Ok I was probably on the right path but I was unable to make that work as a SharePoint HTTP request due to "ill-formed JSON stream" errors.

However, I found another solution which completely solves my issue!

The solution to this problem is to use "Create File" instead of "Add Attachment".

This blog says you need to disable "Allow chunking" and you will be able to overwrite existing SharePoint files, but in my testing that is not necessary. You do not need to disable chunking.

All you need to do is use "Create file" and the file will be created or overwritten seamlessly without having to check if it exists and delete it first! "Add Attachment" gives an error if the file already exists, but "Create File" works whether it exists or not. "Add Attachment" is specific to attaching files to list items, but "Create File" works for any folder in SharePoint. "Lists" is a folder and each list is itself a folder and the attachments to a list is a folder and each list item is a folder.

Therefore, if you want the file to attach to a list item in a SharePoint list, the syntax for "Folder Path" in your "Create File" action is as follows:

/Lists/<List Name>/Attachments/<List Item Id>

In my testing, I am able to concurrently add attachments to the same list item using the "Create File" action, whereas previously the "Add Attachment" action would fail if another "Add Attachment" action was already modifying an attachment to the same list item. I suppose if any two concurrent "Create File" actions tried to create or modify a file with the exact same name, that would cause issues, but as long as all the file names are different, "Create File" seems to have no trouble at all with simultaneously adding several attachments to the same list item!

This has significantly reduced the run times in my flow! I no longer have to run a loop to delete old versions of the attachments and I no longer have to attach them synchronously. Asynchronous is fine with "Create File"! How is this not common knowledge? It seems super important, yet I had to figure this out myself because none of the other threads on this issue mentioned it at all (well until I came across the blog I linked to above).

For my purposes, there is no reason to ever use "Add Attachment" because it's such a weak and error-prone action. You either have to augment it with other actions to prevent the "file already exists" or "record is already being modified" types of errors, or you have to use it only in special circumstances where the file definitely does not exist and the list item is definitely not already being modified concurrently by another "Add Attachment" action.

Why would anyone ever use "Add Attachment" when "Create File" obviates the preemptive deletion of the existing files and also doesn't fail with concurrent/asynchronous actions? I think more folks would use "Create File" instead of "Add Attachment" if they understood this difference and if they understood the folder structure of attachments to list items.