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Python-Flask:動(dòng)態(tài)創(chuàng)建表的示例詳解

更新時(shí)間：2019年11月22日 16:32:23 作者：Odyssues_lee

今天小編就為大家分享一篇Python-Flask:動(dòng)態(tài)創(chuàng)建表的示例詳解，具有很好的參考價(jià)值，希望對(duì)大家有所幫助。一起跟隨小編過來看看吧

今天小編從項(xiàng)目的實(shí)際出發(fā)，由于項(xiàng)目某一個(gè)表的數(shù)據(jù)達(dá)到好幾十萬條，此時(shí)數(shù)據(jù)的增刪查改會(huì)很慢；為了增加提高訪問的速度，我們引入動(dòng)態(tài)創(chuàng)建表。

代碼如下：

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='項(xiàng)目編號(hào)')
  ......
 
 
  @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，內(nèi)層函數(shù)是如何創(chuàng)建的呢？其實(shí)就是拼接sql語句create table ....

代碼如下：

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?cái)?shù)據(jù)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(dòng)態(tài)拼接sql語句， 創(chuàng)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
 
  # 動(dòng)態(tài)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, 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
  
  # 查詢數(shù)據(jù)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)

那么，類似的：

1-如果動(dòng)態(tài)的對(duì)已經(jīng)創(chuàng)建的表格進(jìn)行增刪查改，那么可以用類似的思想，進(jìn)行對(duì)sql語句進(jìn)行拼接,insert select delete update

2-判斷是否存在此字段，進(jìn)去拼接查詢這個(gè)字段查出的數(shù)據(jù)是否為空（count）

3-在原來表的基礎(chǔ)上增加字段，或者修改字段，用alter

以上這篇Python-Flask:動(dòng)態(tài)創(chuàng)建表的示例詳解就是小編分享給大家的全部?jī)?nèi)容了，希望能給大家一個(gè)參考，也希望大家多多支持腳本之家。

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