Saya mengikuti panduan di sini:
http://www.sqlalchemy.org/docs/orm/examples.html?highlight=versioning#versioned-objects
dan menemukan masalah. Saya telah mendefinisikan hubungan saya seperti:
generic_ticker = relation('MyClass', backref=backref("stuffs"))dengan string sehingga tidak peduli tentang urutan impor modul model saya. Ini semua berfungsi dengan baik secara normal, tetapi ketika saya menggunakan meta pembuatan versi saya mendapatkan kesalahan berikut:
sqlalchemy.exc.InvalidRequestError: Saat menginisialisasi Mapper Mapper | MyClass | stuffs, ekspresi 'Trader' gagal menemukan nama ("nama 'MyClass' tidak ditentukan"). Jika ini adalah nama kelas, pertimbangkan untuk menambahkan relasi ini () ke kelas setelah kedua kelas dependen telah ditentukan.
Saya melacak kesalahan tersebut untuk:
File "/home/nick/workspace/gm3/gm3/lib/history_meta.py", line 90, in __init__
mapper = class_mapper(cls)
File "/home/nick/venv/tg2env/lib/python2.6/site-packages/sqlalchemy/orm/util.py", line 622, in class_mapper
mapper = mapper.compile()class VersionedMeta(DeclarativeMeta):
def __init__(cls, classname, bases, dict_):
DeclarativeMeta.__init__(cls, classname, bases, dict_)
try:
mapper = class_mapper(cls)
_history_mapper(mapper)
except UnmappedClassError:
passSaya memperbaiki masalah dengan mencoba: kecuali hal-hal di lambda dan menjalankan semuanya setelah semua impor terjadi. Ini berfungsi tetapi tampaknya sedikit sampah, ada ide tentang cara memperbaikinya adalah cara yang lebih baik?
Terima kasih!
Memperbarui
Masalahnya sebenarnya bukan tentang pesanan impor. Contoh pembuatan versi dirancang sedemikian rupa sehingga mapper memerlukan kompilasi di costructor dari setiap kelas berversi. Dan kompilasi gagal saat kelas terkait belum ditentukan. Dalam kasus hubungan melingkar, tidak ada cara untuk membuatnya bekerja dengan mengubah urutan definisi kelas yang dipetakan.
Perbarui 2
Karena pembaruan di atas menyatakan (saya tidak tahu Anda dapat mengedit posting orang lain di sini :)) ini mungkin karena referensi melingkar. Dalam hal ini mungkin seseorang akan menemukan hack saya berguna (saya menggunakannya dengan turbogears) (Ganti VersionedMeta dan tambahkan create_mappers global di history_meta)
create_mappers = []
class VersionedMeta(DeclarativeMeta):
def __init__(cls, classname, bases, dict_):
DeclarativeMeta.__init__(cls, classname, bases, dict_)
#I added this code in as it was crashing otherwise
def make_mapper():
try:
mapper = class_mapper(cls)
_history_mapper(mapper)
except UnmappedClassError:
pass
create_mappers.append(lambda: make_mapper())Kemudian Anda dapat melakukan sesuatu seperti berikut di model __init__.py Anda
# Import your model modules here.
from myproj.lib.history_meta import create_mappers
from myproj.model.misc import *
from myproj.model.actor import *
from myproj.model.stuff1 import *
from myproj.model.instrument import *
from myproj.model.stuff import *
#setup the history
[func() for func in create_mappers]Dengan cara itu, ia membuat pembuat peta hanya setelah semua kelas telah ditentukan.
Perbarui 3 Sedikit tidak terkait tetapi saya menemukan kesalahan kunci utama duplikat dalam beberapa keadaan (melakukan 2 perubahan ke objek yang sama sekaligus). Solusi saya adalah menambahkan kunci peningkatan otomatis baru. Tentu saja Anda tidak dapat memiliki lebih dari 1 dengan mysql jadi saya harus menghapus kunci utama dari barang-barang yang ada yang digunakan untuk membuat tabel riwayat. Lihat kode keseluruhan saya (termasuk hist_id dan menyingkirkan batasan kunci asing):
"""Stolen from the offical sqlalchemy recpies
"""
from sqlalchemy.ext.declarative import DeclarativeMeta
from sqlalchemy.orm import mapper, class_mapper, attributes, object_mapper
from sqlalchemy.orm.exc import UnmappedClassError, UnmappedColumnError
from sqlalchemy import Table, Column, ForeignKeyConstraint, Integer
from sqlalchemy.orm.interfaces import SessionExtension
from sqlalchemy.orm.properties import RelationshipProperty
from sqlalchemy.types import DateTime
import datetime
from sqlalchemy.orm.session import Session
def col_references_table(col, table):
for fk in col.foreign_keys:
if fk.references(table):
return True
return False
def _history_mapper(local_mapper):
cls = local_mapper.class_
# set the "active_history" flag
# on on column-mapped attributes so that the old version
# of the info is always loaded (currently sets it on all attributes)
for prop in local_mapper.iterate_properties:
getattr(local_mapper.class_, prop.key).impl.active_history = True
super_mapper = local_mapper.inherits
super_history_mapper = getattr(cls, '__history_mapper__', None)
polymorphic_on = None
super_fks = []
if not super_mapper or local_mapper.local_table is not super_mapper.local_table:
cols = []
for column in local_mapper.local_table.c:
if column.name == 'version':
continue
col = column.copy()
col.unique = False
#don't auto increment stuff from the normal db
if col.autoincrement:
col.autoincrement = False
#sqllite falls over with auto incrementing keys if we have a composite key
if col.primary_key:
col.primary_key = False
if super_mapper and col_references_table(column, super_mapper.local_table):
super_fks.append((col.key, list(super_history_mapper.base_mapper.local_table.primary_key)[0]))
cols.append(col)
if column is local_mapper.polymorphic_on:
polymorphic_on = col
#if super_mapper:
# super_fks.append(('version', super_history_mapper.base_mapper.local_table.c.version))
cols.append(Column('hist_id', Integer, primary_key=True, autoincrement=True))
cols.append(Column('version', Integer))
cols.append(Column('changed', DateTime, default=datetime.datetime.now))
if super_fks:
cols.append(ForeignKeyConstraint(*zip(*super_fks)))
table = Table(local_mapper.local_table.name + '_history', local_mapper.local_table.metadata,
*cols, mysql_engine='InnoDB')
else:
# single table inheritance. take any additional columns that may have
# been added and add them to the history table.
for column in local_mapper.local_table.c:
if column.key not in super_history_mapper.local_table.c:
col = column.copy()
super_history_mapper.local_table.append_column(col)
table = None
if super_history_mapper:
bases = (super_history_mapper.class_,)
else:
bases = local_mapper.base_mapper.class_.__bases__
versioned_cls = type.__new__(type, "%sHistory" % cls.__name__, bases, {})
m = mapper(
versioned_cls,
table,
inherits=super_history_mapper,
polymorphic_on=polymorphic_on,
polymorphic_identity=local_mapper.polymorphic_identity
)
cls.__history_mapper__ = m
if not super_history_mapper:
cls.version = Column('version', Integer, default=1, nullable=False)
create_mappers = []
class VersionedMeta(DeclarativeMeta):
def __init__(cls, classname, bases, dict_):
DeclarativeMeta.__init__(cls, classname, bases, dict_)
#I added this code in as it was crashing otherwise
def make_mapper():
try:
mapper = class_mapper(cls)
_history_mapper(mapper)
except UnmappedClassError:
pass
create_mappers.append(lambda: make_mapper())
def versioned_objects(iter):
for obj in iter:
if hasattr(obj, '__history_mapper__'):
yield obj
def create_version(obj, session, deleted = False):
obj_mapper = object_mapper(obj)
history_mapper = obj.__history_mapper__
history_cls = history_mapper.class_
obj_state = attributes.instance_state(obj)
attr = {}
obj_changed = False
for om, hm in zip(obj_mapper.iterate_to_root(), history_mapper.iterate_to_root()):
if hm.single:
continue
for hist_col in hm.local_table.c:
if hist_col.key == 'version' or hist_col.key == 'changed' or hist_col.key == 'hist_id':
continue
obj_col = om.local_table.c[hist_col.key]
# get the value of the
# attribute based on the MapperProperty related to the
# mapped column. this will allow usage of MapperProperties
# that have a different keyname than that of the mapped column.
try:
prop = obj_mapper.get_property_by_column(obj_col)
except UnmappedColumnError:
# in the case of single table inheritance, there may be
# columns on the mapped table intended for the subclass only.
# the "unmapped" status of the subclass column on the
# base class is a feature of the declarative module as of sqla 0.5.2.
continue
# expired object attributes and also deferred cols might not be in the
# dict. force it to load no matter what by using getattr().
if prop.key not in obj_state.dict:
getattr(obj, prop.key)
a, u, d = attributes.get_history(obj, prop.key)
if d:
attr[hist_col.key] = d[0]
obj_changed = True
elif u:
attr[hist_col.key] = u[0]
else:
# if the attribute had no value.
attr[hist_col.key] = a[0]
obj_changed = True
if not obj_changed:
# not changed, but we have relationships. OK
# check those too
for prop in obj_mapper.iterate_properties:
if isinstance(prop, RelationshipProperty) and \
attributes.get_history(obj, prop.key).has_changes():
obj_changed = True
break
if not obj_changed and not deleted:
return
attr['version'] = obj.version
hist = history_cls()
for key, value in attr.iteritems():
setattr(hist, key, value)
obj.version += 1
session.add(hist)
class VersionedListener(SessionExtension):
def before_flush(self, session, flush_context, instances):
for obj in versioned_objects(session.dirty):
create_version(obj, session)
for obj in versioned_objects(session.deleted):
create_version(obj, session, deleted = True)sumber
relation()seharusnyarelationship()Jawaban:
Bagus!
sumber