Tech Talk for Ming and PyMongo

tech_talk_june_17.md

June 17 Tech Talk

Author: Rick Copeland

Ming

What is Ming? MongoDB driver

MongoDB

MongoDB Terminology

Relational	MongoDB
Database	Databse
Table	Collection
Index	Index
Row	Document
Column	Field

BSON: binary format for JSON

Example:

1. Document Primary Key: ID in Relational DB
2. UnixDateTime: ISODateTime('2012-09-17')

db.update({spec}, {update})

MongoDB indexing

1. At most one index is used for any given query/update
2. Most indexes are B-tree based
3. GeoSpatial indexes and queryies
4. Full-text search

Scaling Mongdb

Mongodb uses shards

3 configurations

Drivers

PyMongo

1. Auto-generated _id on client-sides
2. Cursor == Python Generator
3. CRUD
4. .explain() will expalin the query cursors
5. Aggregation

Why Ming?

1. Data has a schema
2. Migration
3. Unit of work -- queue up the updates

Datastore and Session

1. Define Schema
2. Ming Models

Ming Bounus: MIM

1. in memory partial pymongo implmentation
2. Useful for unit tests, Does NOT actually touch the disk db
3. Does NOT Scale

Ming ODM

1. Session -> ODMSession
2. collection.m ... -> MappedClass.query
3. Session actually does stuff
   • Track object identity
   • Track object modifications
   • Unit of work to save everything at once

Integration with python web frameworks

1. ThreadLocalODMSession
2. ming.odm.middleware.MingMiddleware
   • flush
   • clear

Decorators

@something
@something_else
def foo():
  pass
  
def foo():
  pass
something_else(foo)
something(foo)

Another example:

@view(..)
def my_view():
    ...

def view(a, b):
    def decorator(function):
        function.a = a
        function.b = b
        return function
    return decorator

def log(logger, message):
    def decorator(function):
        def wrapper(*args, **kwargs):
            logger.info('ENTER:' + message)
            try:
                result = function(*args, **kwargs)
                logger.info('EXIT (%r): ' + message, result)
                return result
            except Exception as err:
                logger.info('EXCEPTION (%r): ' + message, err)
                raise
        return wrapper
    return decorator

@log(logging.getLogger(__name__), 'Mylog')
def something(a,b):
    pass

def something
_tmp0 = log(...)
something = _tmp0(something)


something == wrapper<...>