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python博客。