今天小編從專案的實際出發，由於專案某一個表的資料達到好幾十萬條，此時資料的增刪查改會很慢；為了增加提高訪問的速度，我們引入動態建立表。

程式碼如下：

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='專案編號')
  ......
 
 
  @staticmethod
  def create_table(project_number)
    table_name = ProjectModel.tablename + projectnumber
    structs = [
      {'fieldname': 'id','type': 'varchar2(50)','primary': True,'default': ''},{'fieldname': 'PROJECTNUMBER','default': 0,'isnull':         
        True},.......
    ]
    app.db.create_table(table_name,structs)

那麼，內層函式是如何建立的呢？其實就是拼接sql語句create table ....

程式碼如下：

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)
 
  # 釋放碎片空間
  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()
 
  # 非返回資料的記錄語句
  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,''
 
  # 動態拼接sql語句， 建立表
  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
 
  # 動態判斷表是否存在 
  def existtable(self,tablename):
    ret,err = self.GetRecordCount("user_all_table","TABLE_NAME='" + tablename +"'")
    return ret>0,err
  
  def GetRecordCount(self,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
  
  # 查詢資料記錄
  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)  
 

那麼，類似的：

1-如果動態的對已經建立的表格進行增刪查改，那麼可以用類似的思想，進行對sql語句進行拼接,insert select delete update

2-判斷是否存在此欄位，進去拼接查詢這個欄位查出的資料是否為空（count）

3-在原來表的基礎上增加欄位，或者修改欄位，用alter

以上這篇Python-Flask:動態建立表的示例詳解就是小編分享給大家的全部內容了，希望能給大家一個參考，也希望大家多多支援我們。