On Wed, Nov 1, 2017 at 9:45 PM, Philip Martin <philip.martin2...@gmail.com> wrote: > Wow. Must have completely missing this in the docs. Thank you for the > sample, it definitely has helped. > > I was looking through the source code and noticed internally many of the DDL > elements inherit from _CreateDropBase versus DDLElement. It looks like in > these cases, the element object is something like a Table object, etc. being > passed in versus something like a table name. Would you say its best > practice to always subclass DDLElement?
as opposed to _CreateDropBase, yes, because _CreateDropBase is marked for internal use right now meaning it might change someday. > > I didn't know about configure_mappers() but that is good to know. Is that > strictly something to be aware of if I am fully using the ORM? it is a thing that happens automatically as soon as you use any of your mappings, such as, you say session.query(MyClass), obj = MyClass(), etc. However if you don't do any of that, configure_mappers() will force the "setup" phase to occur. This is the phase where all the linkages between mappers are resolved, e.g. relationships, and then there's a bunch of event hooks that trigger as well including the __declare_first__(), __declare_last__() hooks. If you app is just running and is going to do metadata.create_all(), then it's possible that this configure step hasn't happened yet as it wasn't in my local testing case. It's easy to forget. > I ran the > example using the declarative style just to build the table query (executing > with an engine, not session) and it seemed to function as exactly as I had > intended, but I'm not very familiar the Session object/ORM. > > > > On Wednesday, November 1, 2017 at 8:03:51 AM UTC-7, Mike Bayer wrote: >> >> you can use a hook like __declare_first__ to make this happen: >> >> class AuditMixin(object): >> """created_at, updated_at, table audit mixin.""" >> >> @classmethod >> def __declare_first__(cls): >> table = getattr(cls, '__table__', None) >> >> if table is not None: >> event.listen( >> table, 'after_create', >> CreateUpdateAtTrigger(table.name)) >> >> event.listen( >> table, 'before_drop', >> DropUpdateAtTrigger(table.name)) >> >> created_at = Column( >> TIMESTAMP(timezone=True), server_default=utcnow(), nullable=False >> ) >> updated_at = Column( >> TIMESTAMP(timezone=True), server_default=utcnow(), >> server_onupdate=FetchedValue(for_update=True), nullable=False >> ) >> >> >> >> however, don't go insane like I just did, and remember to call >> configure_mappers() before you try to create tables, which will >> trigger hooks like __declare_first__(). >> >> There are a lot of other hooks to set these triggers up but since you >> are linking to a mixin, __declare_first__ is the simplest, but needs >> the configure_mappers() step to happen for it to be called. >> >> also your function recipe needs a @compiles, I'm assuming you got that >> from the documentation example. >> >> >> >> >> On Tue, Oct 31, 2017 at 10:49 PM, Philip Martin >> <philip.m...@gmail.com> wrote: >> > I was trying to embed the reference code, but here is the link to the >> > gist I >> > have so far. >> > >> > On Tuesday, October 31, 2017 at 7:46:30 PM UTC-7, Philip Martin wrote: >> >> >> >> >> >> I am attempting to create an audit mixin object that would use a server >> >> side column trigger to set the updated_at timestamp. Ideally, whenever >> >> a >> >> class inherits from a declarative base and this mixin class, the >> >> trigger >> >> statement would be created after the table is created and dropped prior >> >> to >> >> the table being dropped. >> >> >> >> So far, I have my column mixin class, AuditMixin, and I also have added >> >> classes CreateUpdateAtTrigger and DropUpdateAtTrigger to compile the >> >> trigger >> >> DDL create and drop statements. From here, I am a bit unsure how to >> >> proceed >> >> to mount an event to any table's that use this mixin. Any help for >> >> specific >> >> reference examples would be appreciated. Thanks. >> >> >> >> >> >> <script >> >> >> >> src="https://gist.github.com/pmart123/b6681e9d9c6ddc92582143e13c1c6941.js";></script> >> > >> > -- >> > SQLAlchemy - >> > The Python SQL Toolkit and Object Relational Mapper >> > >> > http://www.sqlalchemy.org/ >> > >> > To post example code, please provide an MCVE: Minimal, Complete, and >> > Verifiable Example. 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