Python-Flask:动态创建表的示例详解
今天小编从项目的实际出发，由于项目某一个表的数据达到好几十万条，此时数据的增删查改会很慢；为了增加提高访问的速度，我们引入动态创建表。
代码如下：
from app_factory import app
from sqlalchemy import Column, String, Integer
class ProjectModel(app.db.model, app.db.Mixin):
tablename = 'Project_'
ID = Column(String(50), name='ID', doc='id')
PROJECTNUMBER = Column(String(100), name='PROJECTNUMBER', doc='项目编号')
......
@staticmethod
def create_table(project_number)
table_name = ProjectModel.tablename + projectnumber
structs = [
{'fieldname': 'id', 'type': 'varchar2(50)', 'primary': True, 'default': ''},
{'fieldname': 'PROJECTNUMBER', 'type': 'varchar2(50)', 'default': 0, 'isnull':
True},
.......
]
app.db.create_table(table_name, structs)
那么，内层函数是如何创建的呢？其实就是拼接sql语句create table ....
代码如下：
class SQLAlchemyDB(SQLAlchemy):
def __init__(self, app)
super(SQLAlchemyDB, self).__init__(app)
self.__app = app
self.engine.echo = False
self.conn = self.engine.connect()
self.Model.to_dict() = lambda self：{c.name:getattr(self, c.name, None) for c in self.__table__.columns}
self.Session = sessionmaker(bind=self.engine)
self.ScopedSession = lambda: scoped_session(self.Session)
# 释放碎片空间
def free_idle_space(self):
return self.execute('purge recyclebin')
def connstatus(self):
return self.engine.pool.status()
def close(self):
self.conn.close()
self.engine.dispose()
# 非返回数据的记录语句
def execute(self, sqlexpr)
try:
ret = self.conn.execute(sqlalchemy.text(sqlexpr))
except Exception as err:
return False, str(err)
except sqlalchemy.exc.InvalidRequestError as err:
return False, str(err)
return True, ''
# 动态拼接sql语句， 创建表
def create_table(self, tablename, structs):
fieldinfos = []
for struct in structs:
defaultvalue = struct.get('default')
if defaultvalue :
defaultvalue = "'{0}'".format(defaultvalue) if type(defaultvalue) == 'str' else str(defaultvalue)
fieldinfos.append('{0} {1} {2} {3} {4}'.format(struct['fieldname'], struct['type'], 'primary key' if struct.get('primary') else '', ('default' + defaultvalue) if defaultvalue else '', '' if struct.get('isnull') else 'not null'))
sql = 'create table {0} ({1})'.format(tablename, ','.join(fieldinfos))
ret, err = self.execute(sql)
if ret:
self.__app.sync_record(tablename, 'sql_createtable', {}, sql)
return ret, err
# 动态判断表是否存在
def existtable(self, tablename):
ret, err = self.GetRecordCount("user_all_table", "TABLE_NAME='" + tablename +"'")
return ret>0, err
def GetRecordCount(self, tablename, where= None):
sql = 'select count(*) as num from {0} {1}'.format(tablename,('where' + where)) if where != None else '')
recs, err = self.query(sql)
if recs:
for rec in recs:
return rec['num'], ''
return -1 , err
# 查询数据记录
def query(self, sqlexpr):
try:
recs = self.conn.execute(sqlalchemy.text(sqlexpr)
return recs, ''
expect Exception as err:
return None, str(err)
expect sqlalchemy.exc.InvalidRequestError as err:
return None, str(err)
那么，类似的：
1-如果动态的对已经创建的表格进行增删查改，那么可以用类似的思想，进行对sql语句进行拼接,insert select delete update
2-判断是否存在此字段，进去拼接查询这个字段查出的数据是否为空（count）
3-在原来表的基础上增加字段，或者修改字段，用alter
以上这篇Python-Flask:动态创建表的示例详解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【听图阁-专注于Python设计】。
