señales o desencadenantes en SQLAlchemy

Question

¿SQLAlchemy tiene algo similar al concepto de señal de Django? Básicamente, me gustaría activar algunas funciones cuando guardo previamente o guardo algunos objetos de entidad. Gracias.

Editar: SOLO quiero equivalente de django-señales en SQLAlchemy.

Answer 1

No dejó en claro si está integrando SQLAlchemy y Django, o SÓLO quiere el equivalente de señales de django en SQLAlchemy.

Si desea equivalente de Django señales como post_save, pre_save, pre_delete etc, les remito a la página,

sqlalchemy.orm.interfaces.MapperExtension

Answer 2

es posible que desee considerar la sqlalchemy.orm.SessionExtension así

He aquí algunos código que armé para establecer una ID de propietario en una instancia y establecer una fecha_actualización que hace el trabajo en una aplicación de pilones. la clase OrmExt es donde sucede toda la magia. Y init_model es donde lo conectas.

import logging 
import sqlalchemy as sa 
from sqlalchemy import orm 

from pylons import session 

import datetime 

log = logging.getLogger(__name__) 

class ORMSecurityException(Exception): 
    ''' 
    thrown for security violations in orm layer 
    ''' 
    pass 

def _get_current_user(): 
    log.debug('getting current user from session...') 
    log.debug(session) 
    return session['user'] 

def _is_admin(user): 
    return False 


def set_update_date(instance): 

    if hasattr(instance,'update_date'): 
    instance.update_date = datetime.datetime.now() 

def set_owner(instance): 
    ''' 
    if owner_id, run it through the rules 
    ''' 
    log.info('set_owner') 
    if hasattr(instance, 'owner_id'): 
    log.info('instance.owner_id=%s' % instance.owner_id) 
    u = _get_current_user() 
    log.debug('user: %s' % u.email) 
    if not u: 
     #anonymous users can't save owned objects 
     raise ORMSecurityException() 
    if instance.owner_id==None: 
     #must be new object thus, owned by current user 
     log.info('setting owner on object %s for user: %s' % (instance.__class__.__name__,u.email)) 
     instance.owner_id = u.id 
    elif instance.owner_id!=u.id and not _is_admin(u): 
     #if owner_id does not match user_id and user is not admin VIOLATION 
     raise ORMSecurityException() 
    else: 
     log.info('object is already owned by this user') 
     return #good to go 
else: 
    log.info('%s is not an owned object' % instance.__class__.__name__) 
    return 

def instance_policy(instance): 
    log.info('setting owner for %s' % instance.__class__.__name__) 
    set_owner(instance) 
    log.info('setting update_date for %s' % instance.__class__.__name__) 
    set_update_date(instance) 


class ORMExt(orm.SessionExtension): 
    ''' 
    attempt at managing ownership logic on objects 
    ''' 
    def __init__(self,policy): 
     self._policy = policy 

    def before_flush(self,sqlsess,flush_context,instances): 
     ''' 
     check all instances for owner_id==user.id 
     ''' 
     try: 
      for instance in sqlsess.deleted: 
       try: 
        log.info('running policy for deleted %s' % instance.__class__.__name__) 
        self._policy(instance) 
       except Exception,ex: 
        log.error(ex) 
        raise ex 

      for instance in sqlsess.new: 
       try: 
        log.info('running policy for new %s' % instance.__class__.__name__) 
        self._policy(instance) 
       except Exception,ex: 
        log.error(ex) 
        raise ex 

      for instance in sqlsess.dirty: 
       try: 
        if sqlsess.is_modified(instance,include_collections=False,passive=True): 
         log.info('running policy for updated %s' % instance.__class__.__name__) 
         self._policy(instance) 
       except Exception, ex: 
        log.error(ex) 
        raise ex 

     except Exception,ex: 
      sqlsess.expunge_all() 
      raise ex 

def init_model(engine): 
    """Call me before using any of the tables or classes in the model""" 
    sm = orm.sessionmaker(autoflush=True, autocommit=True, bind=engine,extension=ORMExt(instance_policy)) 
    meta.engine = engine 
    meta.Session = orm.scoped_session(sm) 

Answer 3

Esta es mi opinión a este problema, se utiliza para enviar señales de Louie:

dispatch.py

""" 
Signals dispatching for SQLAlchemy mappers. 
""" 

import louie 
from sqlalchemy.orm.interfaces import MapperExtension 
import signals 


class LouieDispatcherExtension(MapperExtension): 
    """ 
    Dispatch signals using louie on insert, update and delete actions. 
    """ 

    def after_insert(self, mapper, connection, instance): 
     louie.send(signals.after_insert, instance.__class__, 
       instance=instance) 
     return super(LouieDispatcherExtension, self).after_insert(mapper, 
       connection, instance) 

    def after_delete(self, mapper, connection, instance): 
     louie.send(signals.after_delete, instance.__class__, 
       instance=instance) 
     return super(LouieDispatcherExtension, self).after_delete(mapper, 
       connection, instance) 

    def after_update(self, mapper, connection, instance): 
     louie.send(signals.after_update, instance.__class__, 
       instance=instance) 
     return super(LouieDispatcherExtension, self).after_update(mapper, 
       connection, instance) 

    def before_delete(self, mapper, connection, instance): 
     louie.send(signals.before_delete, instance.__class__, 
       instance=instance) 
     return super(LouieDispatcherExtension, self).before_delete(mapper, 
       connection, instance) 

    def before_insert(self, mapper, connection, instance): 
     louie.send(signals.before_insert, instance.__class__, 
       instance=instance) 
     return super(LouieDispatcherExtension, self).before_insert(mapper, 
       connection, instance) 

    def before_update(self, mapper, connection, instance): 
     louie.send(signals.before_update, instance.__class__, 
       instance=instance) 
     return super(LouieDispatcherExtension, self).before_update(mapper, 
       connection, instance) 

signals.py

from louie import Signal 


class after_delete(Signal): pass 
class after_insert(Signal): pass 
class after_update(Signal): pass 
class before_delete(Signal): pass 
class before_insert(Signal): pass 
class before_update(Signal): pass 

Ejemplo de uso:

class MyModel(DeclarativeBase): 

    __mapper_args__ = {"extension": LouieDispatcherExtension()} 

    ID = Column(Integer, primary_key=True) 
    name = Column(String(255)) 

def on_insert(instance): 
    print "inserted %s" % instance 

louie.connect(on_insert, signals.after_insert, MyModel) 

Answer 4

creo que busca `ORM Eventos. Puede encontrar documentación aquí:

http://docs.sqlalchemy.org/en/latest/orm/events.html

Answer 5

Puede utilizar la clase interna MapperExtension:

class YourModel(db.Model): 

    class BaseExtension(MapperExtension): 

     def before_insert(self, mapper, connection, instance): 
      # do something here 

     def before_update(self, mapper, connection, instance): 
      # do something here 

    __mapper_args__ = { 'extension': BaseExtension() } 

    # ....