Add optional session parameter to Document.save #1839

[george-pearson]

• Added an optional session parameter to Document.save method.
• Added a test to ensure the session parameter allows documents to be saved.

Session was added in MongoDB v3.6.0.

This pull request goes some of the way towards supporting MongoDB 4.0 transactions, issue #1839.

[george-pearson]

Aha hmm maybe this pull request is not that useful as it breaks for PyMongo <= 3.6.0 and mongoengine still supports PyMongo 3.5. I'll strip out the first commit and reopen that as a pull request on its own seeing as that could still be useful.

[mzamanzadeh]

hi!

why you don't add an if statement for backward compatibility? I mean some thing like this

if pyMongo.__version__ <= "3.6.0":
     raise Exception
<your contribution>

please add session and transaction support. I really need this :(