Python Cookbook中文版电子书下载
1.问题
为了控制数据的增长，经常需要分表，数据库中存在多张结构相同，表名相关的表，如：
table_201706
table_201707
table_201708
怎么通过SQLAlchemy 或者django查询相关的数据表，而不用每次都创建Model呢
2.解决方法
分别在flask和django下实现，代码如下
2.1 flask+sqlalchemy
# -*-coding:utf-8
class NewDynamicModel(object):
"""
动态产生模型和表的对应关系模型
:param base_cls: 基类模型，虚类，如TemplateModel
:param tb_name: 数据库中对应的表名， 如tb_test_2017
:return: Model class
eg:
'''
class TemplateModel(db.Model):
__abstract__ = True
id = db.Column(db.Integer(), autoincrement=True, primary_key=True)
name = db.Column(db.VARCHAR(32), nullable=False)
Test_2017 = NewDynamicModel(TemplateModel, 'tb_test_2017')
print Test_2017.query.all()
'''
"""
_instance = dict()
def __new__(cls, base_cls, tb_name):
new_cls_name = "%s_To_%s" % (
base_cls.__name__, '_'.join(map(lambda x:x.capitalize(),tb_name.split('_'))))
if new_cls_name not in cls._instance:
model_cls = type(new_cls_name, (base_cls,),
{'__tablename__': tb_name})
cls._instance[new_cls_name] = model_cls
return cls._instance[new_cls_name]
Bug：由于新的数据模型是通过type动态创建的，实际module 下的py文件并不存在该类的代码，因而在通过pickle等方式序列化的时候，会报找不到类的错误。
Fixbug: 通过inspect库，拷贝基类的代码作为副本，并替换tablename 属性，写入临时类定义文件，并引入module。
新的方式实现如下：
class NewDynamicModel(object):
"""
动态产生模型和表的对应关系模型
:param base_cls: 基类模型，虚类，如TemplateModel
:param tb_name: 数据库中对应的表名， 如tb_test_2017
:return: Model class
eg:
'''
class TemplateModel(db.Model):
__abstract__ = True
id = db.Column(db.Integer(), autoincrement=True, primary_key=True)
name = db.Column(db.VARCHAR(32), nullable=False)
Test_2017 = NewDynamicModel(TemplateModel, 'tb_test_2017')
print Test_2017.query.all()
'''
"""
@staticmethod
def get_import_codes(Model):
"""
获取基类的import依赖
:param Model:
:return:
"""
module = inspect.getmodule(Model)
all_codelines = inspect.getsourcelines(module)
import_codes = []
import_codes.append('# -*-coding:utf-8\n')
for i in all_codelines[0]:
match = re.search(r'[from]*[\w|\s]*import [\w|\s]*', i)
if match:
import_codes.append(i)
import_codes.extend(['\n', '\n'])
return import_codes
@staticmethod
def get_codes(Model, new_model_name, tb_name):
"""
获取基类的实现代码
:param Model:
:param new_model_name:
:param tb_name:
:return:
"""
codes = inspect.getsourcelines(Model)[0]
result = []
has_alias_tb_name = False
result.append(codes[0].replace(Model.__name__, new_model_name))
for line in codes[1:]:
match = re.search(r'\s+__tablename__\s+=\s+\'(?P<name>\w+)\'', line)
abstract = re.search(r'(?P<indent>\s+)__abstract__\s+=\s+', line)
if abstract:
del line
continue
if match:
name = match.groupdict()['name']
line = line.replace(name, tb_name)
has_alias_tb_name = True
result.append(line)
if not has_alias_tb_name:
result.append("%s__tablename__ = '%s'\n" % (' ', tb_name))
return result
@staticmethod
def create_new_module(module_name, codes):
"""
创建新表映射类的module文件
:param module_name:
:param codes:
:return:
"""
f_path = os.path.join(CURRENT_PATH, '_tmp/%s.py' % module_name)
fp = open(f_path, 'w')
for i in codes:
fp.write(i)
fp.close()
return import_module('sync_session.models._tmp.%s' % module_name)
_instance = dict()
def __new__(cls, base_cls, tb_name):
new_cls_name = "%s_To_%s" % (
base_cls.__name__, ''.join(map(lambda x: x.capitalize(), tb_name.split('_'))))
if tb_name not in engine.table_names():
raise TableNotExist
if new_cls_name not in cls._instance:
import_codes = cls.get_import_codes(base_cls)
class_codes = cls.get_codes(base_cls, new_cls_name, tb_name)
import_codes.extend(class_codes)
new_module_name = new_cls_name.lower()
new_module = cls.create_new_module(new_module_name, import_codes)
model_cls = getattr(new_module, new_cls_name)
cls._instance[new_cls_name] = model_cls
return cls._instance[new_cls_name]
2.2 django
# -*-coding:utf-8
from django.db import models
class NewDynamicModel(object):
"""
动态产生模型和表的对应关系模型
:param base_cls: 基类模型，虚类，如TemplateModel
:param tb_name: 数据库中对应的表名， 如tb_test_2017
:return: Model class
eg:
'''
class TemplateModel(models.Model):
id = models.AutoField(primary_key=True)
name = models.CharField(max_length=50)
class Meta:
abstract = True
Test_2017 = NewDynamicModel(TemplateModel, 'tb_test_2017')
print Test_2017.objects.all()
'''
"""
_instance = dict()
def __new__(cls, base_cls, tb_name):
new_cls_name = "%s_To_%s" % (
base_cls.__name__, '_'.join(map(lambda x:x.capitalize(),tb_name.split('_'))))
if new_cls_name not in cls._instance:
new_meta_cls = base_cls.Meta
new_meta_cls.db_table = tb_name
model_cls = type(new_cls_name, (base_cls,),
{'__tablename__': tb_name, 'Meta': new_meta_cls, '__module__': cls.__module__})
cls._instance[new_cls_name] = model_cls
return cls._instance[new_cls_name]
以上这篇flask/django 动态查询表结构相同表名不同数据的Model实现方法就是小编分享给大家的全部内容了，希望能给大家一个参考，也希望大家多多支持谷谷点程序。