diff options
Diffstat (limited to 'examples/dialtone.py')
| -rw-r--r-- | examples/dialtone.py | 68 |
1 files changed, 34 insertions, 34 deletions
diff --git a/examples/dialtone.py b/examples/dialtone.py index a89021c..8654ffd 100644 --- a/examples/dialtone.py +++ b/examples/dialtone.py @@ -6,14 +6,14 @@ 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 +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 @@ -24,7 +24,7 @@ except: seq.sort() return seq -# Here is the adapter for every object that we may ever need to +# 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 @@ -33,7 +33,7 @@ class ObjectMapper(object): 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)) @@ -42,19 +42,19 @@ class ObjectMapper(object): 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 @@ -66,14 +66,14 @@ class ObjectMapper(object): return qry, self.getValuesDict() # Here are the objects -class Album(object): - id = 0 +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): @@ -84,7 +84,7 @@ class Order(object): 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. @@ -92,7 +92,7 @@ register_adapter(Order, ObjectMapper) 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() @@ -103,42 +103,42 @@ print adapt(Order()).generateInsert() """ - Discussion -Psycopg 2 has a great new feature: adaptation. The big thing about -adaptation is that it enables the programmer to glue most of the +Psycopg 2 has a great new feature: adaptation. The big thing about +adaptation is that it enables the programmer to glue most of the code out there without many difficulties. -This recipe tries to focus 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 +This recipe tries to focus 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 lines 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 +In these lines 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), + +('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 +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 +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. """ |