SQLAlchemy mapping table with non-ascii columns to class
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27-10-2019 - |
题
item = Table('Item', metadata, autoload=True, autoload_with=engine, encoding = 'cp1257')
class Item(object):
pass
from sqlalchemy.orm import mapper
mapper(Item, item)
I get error:
line 43, in <module>
mapper(Item, item)
File "C:\Python27\lib\site-packages\sqlalchemy\orm\__init__.py", line 890, in mapper
return Mapper(class_, local_table, *args, **params)
File "C:\Python27\lib\site-packages\sqlalchemy\orm\mapper.py", line 211, in __init__
self._configure_properties()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\mapper.py", line 578, in _configure_properties
setparent=True)
File "C:\Python27\lib\site-packages\sqlalchemy\orm\mapper.py", line 618, in _configure_property
self._log("_configure_property(%s, %s)", key, prop.__class__.__name__)
File "C:\Python27\lib\site-packages\sqlalchemy\orm\mapper.py", line 877, in _log
(self.non_primary and "|non-primary" or "") + ") " +
File "C:\Python27\lib\site-packages\sqlalchemy\util.py", line 1510, in __get__
obj.__dict__[self.__name__] = result = self.fget(obj)
File "C:\Python27\lib\site-packages\sqlalchemy\sql\expression.py", line 3544, in description
return self.name.encode('ascii', 'backslashreplace')
UnicodeDecodeError: 'ascii' codec can't decode byte 0xeb in position 7: ordinal not in range(128)
I am connecting to MSSQL. table autoload seems to work. I only get this error while trying to map. Thank you all for help!
解决方案
Mapping the table to a class creates mapped properties on the class. The properties have the same name of the columns, by default. Since python 2.x only allows ascii identifiers, that fails if you have non-ascii column names.
The only solution I can think of is to give the identifiers a different name when mapping the table to a class.
The example below does that. Note that I'm creating the table on the code for simplicity, so anyone can run the code without having existing table. But you could do the same with a reflected table.
#-*- coding:utf-8 -*-
import sqlalchemy as sa
import sqlalchemy.orm
engine = sa.create_engine('sqlite://', echo=True) # new memory-only database
metadata = sa.MetaData(bind=engine)
# create a table. This could be reflected from the database instead:
tb = sa.Table('foo', metadata,
sa.Column(u'id', sa.Integer, primary_key=True),
sa.Column(u'nomé', sa.Unicode(100)),
sa.Column(u'ãéìöû', sa.Unicode(100))
)
tb.create()
class Foo(object):
pass
# maps the table to the class, defining different property names
# for some columns:
sa.orm.mapper(Foo, tb, properties={
'nome': tb.c[u'nomé'],
'aeiou': tb.c[u'ãéìöû']
})
After that you can use Foo.nome
to refer to the nomé
column and Foo.aeiou
to refer to the ãéìöû
column.
其他提示
I faced the same problem and finally managed to do it replacing table['column'].key after autoloading it, just make all your table classes inherit this one and then modify the column name replacement in mapTo method or override manually the desired names with a dictionary and columns_descriptor method. I don't know if this is not the right way to do it but after searching for hours is the best aproach I've got.
class SageProxy(object):
@classmethod
def ismapped(cls, table_name=None):
if mappings:
if table_name:
if mappings.has_key(table_name):
tmap=mappings[table_name]
if tmap.has_key('class'):
tclass=tmap['class']
if tclass is cls:
return True
else:
for m in mappings:
if cls is m['class']:
return True
return False
@classmethod
def mappingprops(cls):
#override this to pass properties to sqlalchemy mapper function
return None
@classmethod
def columns_descriptors(cls):
#override this to map columns to different class properties names
#return dictionary where key is the column name and value is the desired property name
return {}
@classmethod
def mapTo(cls, table_name, map_opts=None):
if not cls.ismapped(table_name):
tab_obj=Table(table_name,sage_md,autoload=True)
for c in tab_obj.c:
#clean field names
tab_obj.c[c.name].key=c.key.replace(u'%',u'Porcentaje').replace(u'ñ',u'ny').replace(u'Ñ',u'NY').replace(u'-',u'_')
for k,v in cls.columns_descriptors():
if tab_obj.c[k]:
tab_obj.c[k].key=v
mapper(cls, tab_obj, properties=cls.mappingprops())
mappings[table_name]={'table':tab_obj,'class':cls}
return cls
I expect it will be usefull
I found that I could do this with a simple addition to my reflected class:
metadata = MetaData(bind=engine, reflect=True)
sm = sessionmaker(bind=engine)
class tblOrders(Base):
__table__ = metadata.tables['tblOrders']
meter = __table__.c['Meter#']
meter
is now mapped to the underlying Meter#
column, which allows this code to work:
currOrder = tblOrders()
currOrder.meter = '5'
Without the mapping, python sees it as a broken statement becase Meter
followed by a comment does not exist in the object.