file-md5 | comput md5 of static file

I'm trying to develop a simple model form by Django to upload pdf files. The form is based on a model. Every time, user upload a file a database table entry would be created with the file path (including filename), uploaded user name and time Etc.

when I upload the same file again, Django is uploading the same file by altering its name (poster-proposal.pdf ->poster-proposal_IomFZQM.pdf). It is also creating another entry in the database table.

I want Django to give the user a warning when he is trying to upload an already existing file saying (a file with the same name is already existing) or something like that and not to upload the duplicate file.

I followed this post,post 1 but it says it does not prevent Django from uploading the file.

I followed this method post 2, but I'm new to Django and it seems complicated. I believe for newer Django versions there should be an easier way to address this issue.

I added unique = True to FileField.It did not work

models.py

Trying to compute incremental md5 digest for all files in deep directory trees, but I'm unable to "reuse" the already calculated digest.

Here is my test-code: