Pass Parameter Upload.aspx Sharepoint Online

For reference and anyone else struggling as I did with this I managed to eventually find a solution.

Firstly on the online Sharepoint it does not look like you can amend Upload.apsx but you can amend the EditForm.aspx. After you upload the file you will be directed to this form to make it work.

So you want to pass the parameter to Upload.aspx, upon posting it will get passed to EditForm.aspx (but a custom one) and you can use the parameter in the form.

Here's how to do it:

• Open up you site in Sharepoint designer
• Go to Lists and Libraries and click on the Documents library
• You should get a sort of summary page with several sections one of which is Forms
• Under the Forms section click New
• Give it a File Name (customedit)
• Select "Edit item form (used to edit existing list items)"
• Select "Set as default form for the selected type" as this will override the EditForm.aspx from being used once the user clicks to upload the file
• Click OK
• Your new form will appear in the Forms section
• Click on it to edit the file
• First we need to define the parameter in the form
• Click in the code either in the WebPartPages:DataFormWebPart tag (line 24 on mine) or below to get the location specific options at the top
• In the top ribbon you should now see Data View Tools
• Click on Options and in the Filter, Sort & Group section click Parameters
• Click on New Parameter and type in the Query String Variable (the field id you are passing in the address) and the Default Value
• It will call it Param1 which you can optionally change but i haven't for the below
• Scroll down until you see (was line 122 on mine)
• Below it should be a table containing your documents fields
• Delete those you don't want to see to tidy up your edit form
• Under the item you want to auto-populate you should see a SharePoint:FormField tab that looks like this <SharePoint:FormField runat="server" id="ff1{$Pos}" ControlMode="Edit" FieldName="SalesforceID" __designer:bind="{ddwrt:DataBind('u',concat('ff1',$Pos),'Value','ValueChanged','ID',ddwrt:EscapeDelims(string(@ID)),'@SalesforceID')}"/>
• Make a note of the ff number (ff1 in the above)
• You want to replace this with <asp:TextBox runat="server" id="ff1{$Pos}" value="{$Param1}" text="" __designer:bind="{ddwrt:DataBind('u',concat('ff1',$Pos),'Text','TextChanged','ID',ddwrt:EscapeDelims(string(@ID)),'@SalesforceID')}"/>
• Replace the ff1 with the number you made a note of in the previous point
• Replace SalesforceID with the field name of your Sharepoint column
• Save and test

Now I figured this out a while ago but wanted to post this for reference so if it doesn't work I may have missed a point but hopefully you get the gist of it.

All that's left for me is figuring out how to auto-populate a unique filename or stop overwriting files. Both I'm failing at miserably