I'm used to using aggregate types in postgres as a convenience. I
whipped up the beginings something analogous to that for django. It
allows definition of "aggregate fields" using a marker base class; it
defines a mixin for Model-derived classes that unpacks "aggregates" and
adds them as individual fields with name prefix at class creation time.
This causes the DB to generate correctly. Still to do: write
descriptors for the original thing to get the values back.
I'm interested in comments: is this a useful feature for anyone else?
Is this the best way to do this? (I'm posting now, before I've
finished, in case someone wants to dissuade me from this approach.)
I should note I found the code in django.db.models to be... relatively
straightforward... but with no obvious hooks for
customization/extension (let alone documentation for this). How do I
implement a custom field type for my favorite db (except as I've just
done: by "cheating", and translating it into already supported things)?
Of course, I should add that django is wonderfully useful, and I
realize that no ones getting paid and the version number is low, so
please don't think I'm complaining.
#
----------------------------------------------------------------------
# Aggregates:
#
----------------------------------------------------------------------
from django.db.models.base import ModelBase
class AggregateField:
"""a marker to signal that a given attribute is actually an
aggregate of fields."""
class WithAggregatesBase( ModelBase ):
def __init__( cls, name, bases, attrs ):
# check if we are really a 'Model'
for base in bases:
if issubclass( base, Model ): break
else:
return super( WithAggregatesBase, cls ).__init__(
cls, name, bases, attrs )
# add parts of aggregates
for atname, at in attrs.items():
if isinstance( at, AggregateField ):
prefix = atname.lower() + '_'
for agname, ag in at.__class__.__dict__.iteritems():
fullAgname = prefix + agname
if fullAgname not in attrs:
attrs[ prefix + agname ] = copy( ag )
cls.add_to_class( fullAgname, ag )
super( WithAggregatesBase, cls ).__init__(
cls, name, bases, attrs )
class WithAggregates( object ):
"""inherit from this AND Model if you want aggregates to be
expanded."""
__metaclass__ = WithAggregatesBase
#
----------------------------------------------------------------------
# Usage Example
#
----------------------------------------------------------------------
class Name( AggregateField ):
first : CharField( maxlength = 60 )
last : CharField( maxlength = 60 )
class Person( Model, WithAggregates ):
name = Name()
-------------------------------------------------
In database, will have name_last, and name_first fields generated.
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From: "shaunc" <[EMAIL PROTECTED]>
To: "Django developers" <[email protected]>
Subject: aggregate field types
Date: Sat, 20 May 2006 22:40:03 -0700
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I'm used to using aggregate types in postgres as a convenience. I
whipped up the beginings something analogous to that for django. It
allows definition of "aggregate fields" using a marker base class; it
defines a mixin for Model-derived classes that unpacks "aggregates" and
adds them as individual fields with name prefix at class creation time.
This causes the DB to generate correctly. Still to do: write
descriptors for the original thing to get the values back.
I'm interested in comments: is this a useful feature for anyone else?
Is this the best way to do this? (I'm posting now, before I've
finished, in case someone wants to dissuade me from this approach.)
I should note I found the code in django.db.models to be... relatively
straightforward... but with no obvious hooks for
customization/extension (let alone documentation for this). How do I
implement a custom field type for my favorite db (except as I've just
done: by "cheating", and translating it into already supported things)?
Of course, I should add that django is wonderfully useful, and I
realize that no ones getting paid and the version number is low, so
please don't think I'm complaining.
#
----------------------------------------------------------------------
# Aggregates:
#
----------------------------------------------------------------------
from django.db.models.base import ModelBase
class AggregateField:
"""a marker to signal that a given attribute is actually an
aggregate of fields."""
class WithAggregatesBase( ModelBase ):
def __init__( cls, name, bases, attrs ):
# check if we are really a 'Model'
for base in bases:
if issubclass( base, Model ): break
else:
return super( WithAggregatesBase, cls ).__init__(
cls, name, bases, attrs )
# add parts of aggregates
for atname, at in attrs.items():
if isinstance( at, AggregateField ):
prefix = atname.lower() + '_'
for agname, ag in at.__class__.__dict__.iteritems():
fullAgname = prefix + agname
if fullAgname not in attrs:
attrs[ prefix + agname ] = copy( ag )
cls.add_to_class( fullAgname, ag )
super( WithAggregatesBase, cls ).__init__(
cls, name, bases, attrs )
class WithAggregates( object ):
"""inherit from this AND Model if you want aggregates to be
expanded."""
__metaclass__ = WithAggregatesBase
#
----------------------------------------------------------------------
# Usage Example
#
----------------------------------------------------------------------
class Name( AggregateField ):
first : CharField( maxlength = 60 )
last : CharField( maxlength = 60 )
class Person( Model, WithAggregates ):
name = Name()
-------------------------------------------------
In database, will have name_last, and name_first fields generated.
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