Getting 'TypeError: ObjectId('') is not JSON serializable' when using Flask 0.10.1

Question

I forked the Flask example, Minitwit, to work with MongoDB and it was working fine on Flask 0.9, but after upgrading to 0.10.1 I get the error in title when I login when I try t

Answer 1

toString converts it to the string and that can stored to session:

session['_id'] = user['_id'].toString()

alternative session['_id'] = str(user['_id'])

The above fixed the error for me.