flask/django 动态查询表结构相同表名不同数据的Model实现方法

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我们。