flask/django 动态查询表结构相同表名不同数据的Model实现方法
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2023-08-13 22:52:03
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_201...
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]
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