+++ /dev/null
-"""
-This example/recipe has been contributed by Valentino Volonghi (dialtone)
-
-Mapping arbitrary objects to a PostgreSQL database with psycopg2
-
-- Problem
-
-You need to store arbitrary objects in a PostgreSQL database without being
-intrusive for your classes (don't want inheritance from an 'Item' or
-'Persistent' object).
-
-- Solution
-"""
-
-from datetime import datetime
-
-import psycopg2
-from psycopg2.extensions import adapt, register_adapter
-
-try:
- sorted()
-except:
- def sorted(seq):
- seq.sort()
- return seq
-
-# Here is the adapter for every object that we may ever need to
-# insert in the database. It receives the original object and does
-# its job on that instance
-
-class ObjectMapper(object):
- def __init__(self, orig, curs=None):
- self.orig = orig
- self.tmp = {}
- self.items, self.fields = self._gatherState()
-
- def _gatherState(self):
- adaptee_name = self.orig.__class__.__name__
- fields = sorted([(field, getattr(self.orig, field))
- for field in persistent_fields[adaptee_name]])
- items = []
- for item, value in fields:
- items.append(item)
- return items, fields
-
- def getTableName(self):
- return self.orig.__class__.__name__
-
- def getMappedValues(self):
- tmp = []
- for i in self.items:
- tmp.append("%%(%s)s"%i)
- return ", ".join(tmp)
-
- def getValuesDict(self):
- return dict(self.fields)
-
- def getFields(self):
- return self.items
-
- def generateInsert(self):
- qry = "INSERT INTO"
- qry += " " + self.getTableName() + " ("
- qry += ", ".join(self.getFields()) + ") VALUES ("
- qry += self.getMappedValues() + ")"
- return qry, self.getValuesDict()
-
-# Here are the objects
-class Album(object):
- id = 0
- def __init__(self):
- self.creation_time = datetime.now()
- self.album_id = self.id
- Album.id = Album.id + 1
- self.binary_data = buffer('12312312312121')
-
-class Order(object):
- id = 0
- def __init__(self):
- self.items = ['rice','chocolate']
- self.price = 34
- self.order_id = self.id
- Order.id = Order.id + 1
-
-register_adapter(Album, ObjectMapper)
-register_adapter(Order, ObjectMapper)
-
-# Describe what is needed to save on each object
-# This is actually just configuration, you can use xml with a parser if you
-# like to have plenty of wasted CPU cycles ;P.
-
-persistent_fields = {'Album': ['album_id', 'creation_time', 'binary_data'],
- 'Order': ['order_id', 'items', 'price']
- }
-
-print adapt(Album()).generateInsert()
-print adapt(Album()).generateInsert()
-print adapt(Album()).generateInsert()
-print adapt(Order()).generateInsert()
-print adapt(Order()).generateInsert()
-print adapt(Order()).generateInsert()
-
-"""
-- Discussion
-
-Psycopg 2 has a great new feature: adaptation. The big thing about
-adaptation is that it enable the programmer to glue most of the
-code out there without many difficulties.
-
-This recipe tries to focus the attention on a way to generate SQL queries to
-insert completely new objects inside a database. As you can see objects do
-not know anything about the code that is handling them. We specify all the
-fields that we need for each object through the persistent_fields dict.
-
-The most important lines of this recipe are:
- register_adapter(Album, ObjectMapper)
- register_adapter(Order, ObjectMapper)
-
-In these line we notify the system that when we call adapt with an Album instance
-as an argument we want it to istantiate ObjectMapper passing the Album instance
-as argument (self.orig in the ObjectMapper class).
-
-The output is something like this (for each call to generateInsert):
-
-('INSERT INTO Album (album_id, binary_data, creation_time) VALUES
- (%(album_id)s, %(binary_data)s, %(creation_time)s)',
-
- {'binary_data': <read-only buffer for 0x402de070, ...>,
- 'creation_time': datetime.datetime(2004, 9, 10, 20, 48, 29, 633728),
- 'album_id': 1}
-)
-
-This is a tuple of {SQL_QUERY, FILLING_DICT}, and all the quoting/converting
-stuff (from python's datetime to postgres s and from python's buffer to
-postgres' blob) is handled with the same adaptation process hunder the hood
-by psycopg2.
-
-At last, just notice that ObjectMapper is working for both Album and Order
-instances without any glitches at all, and both classes could have easily been
-coming from closed source libraries or C coded ones (which are not easily
-modified), whereas a common pattern in todays ORMs or OODBs is to provide
-a basic 'Persistent' object that already knows how to store itself in the
-database.
-"""
git://git.onelab.eu / plcapi.git / blobdiff