I have been checking on the issue of ActiveMapper, regarding its use
when classes with multiple inter-relations are involved. It quickly
became evident that if you intend to use ActiveMapper for a case where
the complexity of the classes goes a little beyond the test case, the
code fails, except you take extreme care with the ordering of the
classes, and even so there are times where you can´t do this, because
there are constraints that come from the table declarations that collide
with the constraints for the ordering of the classes regarding their
relationships.
Anyway...I think I´ve managed to modify ActiveMapper to lessen this
problem, maybe even solve it completely (at least to the extent of my
testing it works just fine). This modification is barely more than a
dirty hack, but it "just works". What I did was decouple the table
creation phase from the relations processing, which now must be started
"by hand", calling the function "connect_classes". Upon calling this
function, the system will check everyclass asociated with
ActiveMapperMeta, and will order them in the correct order for
everything to work fine.
So, without further ado I will copy the code of the modified
ActiveMapper...if someone can test it (I´ve tried 6 interconnected
classes and there seemed to be no problems) it should prove a good
addittion to the SVN repository. The usage method is the exact same as
always, but you need to call activemapper.connect_classes prior using
the classes. You should be able to shuffle the ordering of the
declaration of the classes without repercusions...
Best Regards,
Gabriel.
activemapper.py
---
from sqlalchemy import objectstore, create_engine,
assign_mapper, relation, mapper
from sqlalchemy import and_, or_
from sqlalchemy import Table, Column, ForeignKey
from sqlalchemy.ext.proxy import ProxyEngine
import inspect
import sys
#
# the "proxy" to the database engine... this can be swapped out at runtime
#
engine = ProxyEngine()
#
# declarative column declaration - this is so that we can infer the colname
#
class column(object):
def __init__(self, coltype, colname=None, foreign_key=None,
primary_key=False, *args, **kwargs):
if isinstance( foreign_key, basestring ):
foreign_key= ForeignKey( foreign_key )
self.coltype = coltype
self.colname = colname
self.foreign_key = foreign_key
self.primary_key = primary_key
# self.unique = kwargs.pop( 'unique', None )
# self.index = kwargs.pop( 'indexed', None )
self.kwargs = kwargs
self.args = args
#
# declarative relationship declaration
#
class relationship(object):
def __init__(self, classname, colname=None, backref=None, private=False,
lazy=True, uselist=True, secondary=None):
self.classname = classname
self.colname = colname
self.backref = backref
self.private = private
self.lazy = lazy
self.uselist = uselist
self.secondary = secondary
class one_to_many(relationship):
def __init__(self, classname, colname=None, backref=None,
private=False, lazy=True):
relationship.__init__(self, classname, colname, backref,
private, lazy, uselist=True)
class one_to_one(relationship):
def __init__(self, classname, colname=None, backref=None,
private=False, lazy=True):
relationship.__init__(self, classname, colname, backref,
private, lazy, uselist=False)
class many_to_many(relationship):
def __init__(self, classname, secondary, backref=None, lazy=True):
relationship.__init__(self, classname, None, backref, False, lazy,
uselist=True, secondary=secondary)
#
# SQLAlchemy metaclass and superclass that can be used to do SQLAlchemy
# mapping in a declarative way, along with a function to process the
# relationships between dependent objects as they come in, without blowing
# up if the classes aren't specified in a proper order
#
__deferred_classes__ = []
def process_relationships(klass, was_deferred=False):
defer = False
for propname, reldesc in klass.relations.items():
if not reldesc.classname in ActiveMapperMeta.classes:
if not was_deferred: __deferred_classes__.append(klass)
defer = True
if not defer:
relations = {}
for propname, reldesc in klass.relations.items():
relclass = ActiveMapperMeta.classes[reldesc.classname]
relations[propname] = relation(relclass.mapper,
secondary=reldesc.secondary,
backref=reldesc.backref,
private=reldesc.private,
lazy=reldesc.lazy,
uselist=reldesc.uselist)
if len(relations)>0:
assign_mapper(klass, klass.table, properties=relations)
if was_deferred: __deferred_classes__.remove(klass)
if not was_deferred:
for deferred_class in __deferred_classes__:
process_relationships(deferred_class, was_deferred=True)
class ActiveMapperMeta(type):
classes = {}
def __init__(cls, clsname, bases, dict):
table_name = clsname.lower()
columns = []
relations = {}
_engine = getattr( sys.modules[cls.__module__], "__engine__",
engine )
if 'mapping' in dict:
members = inspect.getmembers(dict.get('mapping'))
for name, value in members:
if name == '__table__':
table_name = value
continue
if '__engine__' == name:
_engine= value
continue
if name.startswith('__'): continue
if isinstance(value, column):
if value.foreign_key:
col = Column(value.colname or name,
value.coltype,
value.foreign_key,
primary_key=value.primary_key,
*value.args, **value.kwargs)
else:
col = Column(value.colname or name,
value.coltype,
primary_key=value.primary_key,
*value.args, **value.kwargs)
columns.append(col)
# if value.indexed:
# # create a Index object for the column
# index= Index( "%s_idx" % (value.colname or name),
# col, unique= value.unique )
continue
if isinstance(value, relationship):
relations[name] = value
assert _engine is not None, "No engine specified"
cls.table = Table(table_name, _engine, *columns)
assign_mapper(cls, cls.table)
cls.relations = relations
ActiveMapperMeta.classes[clsname] = cls
#process_relationships(cls)
super(ActiveMapperMeta, cls).__init__(clsname, bases, dict)
class ActiveMapper(object):
__metaclass__ = ActiveMapperMeta
def set(self, **kwargs):
for key, value in kwargs.items():
setattr(self, key, value)
#
# a utility function to create all tables for all ActiveMapper classes
#
def create_tables():
for klass in ActiveMapperMeta.classes.values():
klass.table.create()
def connect_classes():
#Order classes according to their relationships for processing the
relationships in the appropriate order.
mylist = []
for cls in ActiveMapperMeta.classes:
relations = ActiveMapperMeta.classes[cls].relations
behind = 0
r = range(len(mylist))
#Test every relation of this class against the ones already in the
mylist
for relname in relations:
for x in r:
if mylist[x] == relations[relname].classname:
behind = x+1
#Test every relation of the classes in the mylist against this class
for x in r:
relations = ActiveMapperMeta.classes[mylist[x]].relations
for relname in relations:
if mylist[x] == relations[relname].classname:
if behind <= x:
behind = x+1
mylist.insert(behind, cls)
#Process relationships according to the given order
for cls in mylist:
process_relationships(ActiveMapperMeta.classes[cls])
-------------------------------------------------------
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