Required column, document libraries and file explorer
Question: If you have a required column in a document library how can does a value for this column get set when a document is copied into the library through the file explorer?
Answer: From a document library you can select the Actions + Open with File Explorer menu command, and then drag and drop files into the document library through the File Explorer. However, File Explorer does not have an interface for collecting column values, and so cannot honour required fields.
When you copy a file into a document library through File Explorer the file will be checked out, and a checked out document does not have to have a value for a required field. When the document is checked in through SharePoint the following message is displayed:
You need to edit the properties for the document to set a value for the required field, and then check it in.
For document libraries that have required fields but do not require a check-out to modify documents – new documents added through the file explorer will be checked out and so values for the required fields must be provided when the document is checked in.