SQLAlchemy "event.listen" for all models

Question

I have fields created_by and updated_by in each models. These fields are automatically filled with sqlalchemy.event.listen (formerly MapperExtension). For each model, I write:

event.listen(Equipment, 'before_insert', get_created_by_id)
event.listen(Equipment, 'before_update', get_updated_by_id)

When the model was a lot of code gets ugly. Is it possible to apply event.listen immediately to all models or several?

UPD: I'm trying to do so:

import pylons
from sqlalchemy import event, sql
from sqlalchemy import Table, ForeignKey, Column
from sqlalchemy.databases import postgresql
from sqlalchemy.schema import UniqueConstraint, CheckConstraint
from sqlalchemy.types import String, Unicode, UnicodeText, Integer, DateTime,\
                             Boolean, Float
from sqlalchemy.orm import relation, backref, synonym, relationship
from sqlalchemy import func
from sqlalchemy import desc
from sqlalchemy.orm.exc import NoResultFound

from myapp.model.meta import Session as s
from myapp.model.meta import metadata, DeclarativeBase

from pylons import request

def created_by(mapper, connection, target):
    identity = request.environ.get('repoze.who.identity')
    if identity:
        id = identity['user'].user_id
        target.created_by = id

def updated_by(mapper, connection, target):
    identity = request.environ.get('repoze.who.identity')
    if identity:
        id = identity['user'].user_id
        target.updated_by = id

from sqlalchemy.ext.declarative import declared_attr
from sqlalchemy.ext.declarative import has_inherited_table

class TestMixin(DeclarativeBase):
    __tablename__ = 'TestMixin'

    id =  Column(Integer, autoincrement=True, primary_key=True)

event.listen(TestMixin, 'before_insert', created_by)
event.listen(TestMixin, 'before_update', updated_by)

class MyClass(TestMixin):
    __tablename__ = 'MyClass'
    __mapper_args__ = {'concrete':True}

    id =  Column(Integer, autoincrement=True, primary_key=True)

    created_by = Column(Integer, ForeignKey('user.user_id',
                        onupdate="cascade", ondelete="restrict"))

    updated_by = Column(Integer, ForeignKey('user.user_id',
                        onupdate="cascade", ondelete="restrict"))

When I add a new MyClass object I have created_by = None. If I create event.listen for MyClass all is fine. What's wrong?

I found the answer here http://stackoverflow.com/questions/12753450/sqlalchemy-mixins-and-event-listener — uralbash, Apr 16 '14 at 14:09

score 18 · Answer 1 · edited May 17 '18 at 15:04

18

Inherit all your models from the base class and subscribe to that base class:

event.listen(MyBaseMixin, 'before_insert', get_created_by_id, propagate=True)
event.listen(MyBaseMixin, 'before_update', get_updated_by_id, propagate=True)

See more on Mixin and Custom Base Classes

edited May 17 '18 at 15:04

Community

1
1

answered Jan 18 '12 at 13:51

van

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This is my code http://pastebin.com/vzsR5hde I'm trying to use Mixin but get an error: sqlalchemy.exc.InvalidRequestError: Table 'ttt' is already defined for this MetaData instance. Specify 'extend_existing=True' to redefine options and columns on an existing Table object. – uralbash Jan 23 '12 at 07:29
@uralbash Your `LogMixin` is not actually a mix-in class, but a mapped "model" class, since it inherits from `DeclarativeBase`. Now you map other `Net` class that uses the same declared table, but more columns. – Denis Otkidach Jan 27 '12 at 16:01
2

This doesn't seem to work (anymore?) in 0.9.6. SQLAlchemy will let me bind a listener to my base mixin class, but the listener never gets called. If I add the same listener to a specific model class, it gets called. (And yes, it's an actual mix-in class :)) – mmitchell Feb 13 '15 at 19:22
8

You need to add `propagate=True`, if I understood http://docs.sqlalchemy.org/en/rel_0_8/orm/events.html correctly – moritz Feb 26 '15 at 11:08

score 2 · Accepted Answer · answered Nov 27 '20 at 23:14

In newer versions of sqlalchemy (1.2+), the following event targets are available:

mapped classes (that is, subscribe to every model)
unmapped superclasses (that is, Base, and mixins, using the propagate=True flag)
Mapper objects
Mapper class itself

So, in order to listen to all instance events, you can listen on Mapper itself:

from typing import Set, Optional

import sqlalchemy as sa
import sqlalchemy.orm.query
import sqlalchemy.event

@sa.event.listens_for(sa.orm.Mapper, 'refresh', named=True)
def on_instance_refresh(target: type, 
                        context: sa.orm.query.QueryContext, 
                        attrs: Optional[Set[str]]):
    ssn: sqlalchemy.orm.Session = context.session
    print(target, attrs)

this way you will get an app-wide event listener. If you want to only listen to your own models, use the Base class

SQLAlchemy "event.listen" for all models

2 Answers2