Python SQLAlchemy给出了;元数据未绑定到引擎或连接“;
我有以下代码来创建数据库:Python SQLAlchemy给出了;元数据未绑定到引擎或连接“;,python,sqlalchemy,Python,Sqlalchemy,我有以下代码来创建数据库: 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__(sel
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GUI的QMainWindow类的一部分时,它运行良好,没有错误。但当我将它从GUI分离成一个单独的模块时,它开始给我这个错误。以下是回溯:
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?多谢各位
[已解决]
多谢各位。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。如果对话框选择一个文件,则使用该数据库。否则,请使用找到的DB文件
现在可以这样做了:
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()
在调用
db\u utils.db\u create\u voltdrop()
之前,您没有调用db\u utils.db\u open()
因此,当调用metadata.create_all(self.db)
时,db_utils.db
的值为None
。确保在调用db\u utils.db\u open()
之前调用db\u utils.db\u create\u voltdrop()
可以解决问题
metadata.create_all(None)
引发sqlalchemy.exc.UnboundExecutionError
,而不是ValueError
的原因是它们允许您执行以下操作:
metadata.bind = self.db
metadata.create_all()
请你写下产生问题的代码好吗?我复制过去的代码,但它为我工作。这是我想要的。