generate serial number in mongodb

gistfile1.py

>>> import pymongo
>>> 
>>> db = pymongo.Connection('localhost', 27017).somedb  # specify "somedb" db
>>> db.serialnum.insert({"student_id": "kamiya", "seq": 0})  # add seed entry for a student "kamiya" in "serialnum" table
>>> db.serialnum.find_and_modify({"student_id": "kamiya"}, update={"$inc": {"seq": 1}}, new=True)["seq"]  # generate a serial number for "kamiya"
>>> db.serialnum.find_and_modify({"student_id": "kamiya"}, update={"$inc": {"seq": 1}}, new=True)["seq"]  # generate another serial number for "kamiya"

make a function for the above operation...

>>> def init_serial_number(student_id, db):
>>>     db.serialnum.insert({"student_id": student_id, "seq": 0})
>>> 
>>> def gen_serial_number(student_id, db):
>>>     return db.serialnum.find_and_modify({"student_id": student_id}, update={"$inc": {"seq": 1}}, new=True)["seq"]

now you can write as follows:

>>> db = pymongo.Connection('localhost', 27017).somedb  # specify "somedb" db
>>> init_serial_number("kamiya", db)
>>> gen_serial_number("kamiya", db)
>>> gen_serial_number("kamiya", db)

>>> init_serial_number("umemoto", db)  # make an entry for another student
>>> gen_serial_number("umemoto", db)