作者热门文章
- c - 在位数组中找到第一个零
- linux - Unix 显示有关匹配两种模式之一的文件的信息
- 正则表达式替换多个文件
- linux - 隐藏来自 xtrace 的命令
我想向现有的映射类添加一个字段,我将如何自动更新 sql 表。如果将字段添加到类中,sqlalchemy 是否提供一种使用新列更新数据库的方法。
最佳答案
有时迁移工作量太大 - 您只想在运行更改后的代码时自动添加列。所以这里有一个函数可以做到这一点。
注意事项:它在 SQLAlchemy 的内部结构中四处游荡,并且每次 SQLAlchemy 进行重大修订时往往需要进行小的更改。 (可能有更好的方法来做到这一点——我不是 SQLAlchemy 专家)。它也不处理约束。
import logging
import re
import sqlalchemy
from sqlalchemy import MetaData, Table, exceptions
import sqlalchemy.engine.ddl
_new_sa_ddl = sqlalchemy.__version__.startswith('0.7')
def create_and_upgrade(engine, metadata):
"""For each table in metadata, if it is not in the database then create it.
If it is in the database then add any missing columns and warn about any columns
whose spec has changed"""
db_metadata = MetaData()
db_metadata.bind = engine
for model_table in metadata.sorted_tables:
try:
db_table = Table(model_table.name, db_metadata, autoload=True)
except exceptions.NoSuchTableError:
logging.info('Creating table %s' % model_table.name)
model_table.create(bind=engine)
else:
if _new_sa_ddl:
ddl_c = engine.dialect.ddl_compiler(engine.dialect, None)
else:
# 0.6
ddl_c = engine.dialect.ddl_compiler(engine.dialect, db_table)
# else:
# 0.5
# ddl_c = engine.dialect.schemagenerator(engine.dialect, engine.contextual_connect())
logging.debug('Table %s already exists. Checking for missing columns' % model_table.name)
model_columns = _column_names(model_table)
db_columns = _column_names(db_table)
to_create = model_columns - db_columns
to_remove = db_columns - model_columns
to_check = db_columns.intersection(model_columns)
for c in to_create:
model_column = getattr(model_table.c, c)
logging.info('Adding column %s.%s' % (model_table.name, model_column.name))
assert not model_column.constraints, \
'Arrrgh! I cannot automatically add columns with constraints to the database'\
'Please consider fixing me if you care!'
model_col_spec = ddl_c.get_column_specification(model_column)
sql = 'ALTER TABLE %s ADD %s' % (model_table.name, model_col_spec)
engine.execute(sql)
# It's difficult to reliably determine if the model has changed
# a column definition. E.g. the default precision of columns
# is None, which means the database decides. Therefore when I look at the model
# it may give the SQL for the column as INTEGER but when I look at the database
# I have a definite precision, therefore the returned type is INTEGER(11)
for c in to_check:
model_column = model_table.c[c]
db_column = db_table.c[c]
x = model_column == db_column
logging.debug('Checking column %s.%s' % (model_table.name, model_column.name))
model_col_spec = ddl_c.get_column_specification(model_column)
db_col_spec = ddl_c.get_column_specification(db_column)
model_col_spec = re.sub('[(][\d ,]+[)]', '', model_col_spec)
db_col_spec = re.sub('[(][\d ,]+[)]', '', db_col_spec)
db_col_spec = db_col_spec.replace('DECIMAL', 'NUMERIC')
db_col_spec = db_col_spec.replace('TINYINT', 'BOOL')
if model_col_spec != db_col_spec:
logging.warning('Column %s.%s has specification %r in the model but %r in the database' %
(model_table.name, model_column.name, model_col_spec, db_col_spec))
if model_column.constraints or db_column.constraints:
# TODO, check constraints
logging.debug('Column constraints not checked. I am too dumb')
for c in to_remove:
model_column = getattr(db_table.c, c)
logging.warning('Column %s.%s in the database is not in the model' % (model_table.name, model_column.name))
def _column_names(table):
# Autoloaded columns return unicode column names - make sure we treat all are equal
return set((unicode(i.name) for i in table.c))
关于python - SqlAlchemy 向类中添加新字段并在表中创建相应的列,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/2103274/
我在 Java 中遇到异常处理问题,这是我的代码。当我尝试运行此行时出现编译器错误:throw new MojException("Bledne dane");。错误是: exception MojE
我刚刚开始学习asp.net。在你们的支持下,我希望我能从这个论坛学到更多东西。 我的问题是, 我在 asp.net 页面中有一个 TabContainer1,因为每个选项卡面板中有多个类似 (60)
我是一名优秀的程序员,十分优秀!