我有这个代码来创建数据库:
from sqlalchemy import create_engine
from sqlalchemy import Table, Column, Integer, String, Float, MetaData, ForeignKey
from sqlalchemy.sql import select, and_
from PyQt4 import QtGui, QtCore
class DbUtils(object):
def __init__(self, db_file = None, parent = None):
self.db = None
self.db_connection = None
self.db_file = str(db_file)
def db_open(self):
self.db = create_engine('sqlite:///' + self.db_file)
self.db_connection = self.db.connect()
def db_close(self):
self.db_connection.close()
def db_create_voltdrop(self):
metadata = MetaData()
tb_cable_brands = Table('cable_brands', metadata,
Column('id', Integer, primary_key=True),
Column('brand', String)
)
tb_cable_types = Table('cable_types', metadata,
Column('id', Integer, primary_key=True),
Column('brand_id', None, ForeignKey('cable_brands.id')),
Column('type', String),
Column('alpha', String)
)
tb_cable_data = Table('cable_data', metadata,
Column('id', Integer, primary_key=True),
Column('type_id', None, ForeignKey('cable_types.id')),
Column('size', String),
Column('resistance', Float)
)
metadata.create_all(self.db) # db_utils.py", line 67
当它是我的GUI的QMainWindow类的一部分时,它工作正常,没有错误。但是当我将它从GUI分离到一个单独的模块时,它开始给我这个错误。这是一个追溯:
Traceback (most recent call last):
File "C:\Temp\xxx\applications\voltdrop\mainwindow.py", line 52, in __init__
self.main_ui()
File "C:\Temp\xxx\applications\voltdrop\mainwindow.py", line 212, in main_ui
self.db_utils.db_create_voltdrop()
File "C:\Temp\xxx\scripts\db_utils.py", line 67, in db_create_voltdrop
metadata.create_all(self.db)
File "C:\Temp\PortablePython\App\lib\site-packages\sqlalchemy\schema.py", line 2511, in create_all
bind = _bind_or_error(self)
File "C:\Temp\PortablePython\App\lib\site-packages\sqlalchemy\schema.py", line 3124, in _bind_or_error
raise exc.UnboundExecutionError(msg)
sqlalchemy.exc.UnboundExecutionError:
The MetaData is not bound to an Engine or Connection.
Execution can not proceed without a database to execute against.
Either execute with an explicit connection or assign the MetaData's .bind to enable implicit execution.
self.db_utils = DbUtils(self.cabledata_db, self)
self.main_ui() # mainwindow.py", line 52
def main_ui(self):
...
if not self.find_data_file(self.cabledata_db):
file = self.select_data_file("cable")
if file:
self.cabledata_db = file
self.db_utils.db_open()
else:
self.db_utils.db_create_voltdrop() # mainwindow.py", line 212
我做错了什么?谢谢。
[解决]
谢谢。它的工作原理如下:如果没有DB文件,打开对话框并选择一个,如果对话框被取消,则创建一个空DB。如果对话框选择文件,请使用该DB。否则,请使用找到的DB文件。
现在可以使用:
if not self.find_data_file(self.cabledata_db):
file = self.select_data_file("cable")
if file:
self.cabledata_db = file
self.db_utils.db_open()
else:
self.db_utils.db_open()
self.db_utils.db_create_voltdrop()
else:
self.db_utils.db_open()
答案 0 :(得分:6)
如果没有提交,请在致电db_utils.db_open()
之前致电db_utils.db_create_voltdrop()
。
因此,调用db_utils.db
时None
的值为metadata.create_all(self.db)
。确保在致电db_utils.db_open()
之前致电db_utils.db_create_voltdrop()
应该可以解决您的问题。
metadata.create_all(None)
引发sqlalchemy.exc.UnboundExecutionError
而不是ValueError
的原因是他们允许您这样做:
metadata.bind = self.db
metadata.create_all()