Re: [sqlalchemy] mapper_configured event, class fully configured?

[Ladislav Lenart]

On 27.8.2015 22:13, Douglas Russell wrote:
> Ok, thanks, that makes sense.
> 
> Generally everything I see about SQLAlchemy referencing is using backref and 
> it
> is convenient, but knowing that you actually think back_populates would be 
> your
> preferred way to implement things is quite nice. I quite prefer that as I 
> think
> it makes my code much more readable to have the relationship properties 
> declared
> where they will exist.

+100

I came to the same conclusion a long time ago and have never looked back :-)

Just my 2c,

Ladislav Lenart


> Cheers,
> 
> Douglas
> 
> On Monday, 24 August 2015 21:54:17 UTC-4, Michael Bayer wrote:
> 
> 
> 
> On 8/24/15 9:21 PM, Mike Bayer wrote:
>>
>>
>> On 8/24/15 7:41 PM, Douglas Russell wrote:
>>>
>>> |
>>> def print_stuff(mapper, class_):
>>> print getattr(class_, 'books')
>>>
>>> event.listen(mapper, 'mapper_configured', print_stuff)
>>>
>>> author = Author(name='Chuck Paluhniuk')
>>> |
>>>
>>> When I run this code, the result is that when Author is first used, the
>>> 'mapper_configured' event will fire and my print_stuff function callback
>>> will run.
>>>
>>> The results is this:
>>>
>>> |
>>> Traceback (most recent call last):
>>>   File "marshmallow_experiment.py", line 37, in 
>>> author = Author(name='Chuck Paluhniuk')
>>>   File "", line 2, in __init__
>>>   File
>>> 
>>> "/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/orm/instrumentation.py",
>>> line 347, in _new_state_if_none
>>> state = self._state_constructor(instance, self)
>>>   File
>>> 
>>> "/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/util/langhelpers.py",
>>> line 747, in __get__
>>> obj.__dict__[self.__name__] = result = self.fget(obj)
>>>   File
>>> 
>>> "/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/orm/instrumentation.py",
>>> line 177, in _state_constructor
>>> self.dispatch.first_init(self, self.class_)
>>>   File
>>> 
>>> "/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/event/attr.py",
>>> line 258, in __call__
>>> fn(*args, **kw)
>>>   File
>>> 
>>> "/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py",
>>> line 2792, in _event_on_first_init
>>> configure_mappers()
>>>   File
>>> 
>>> "/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py",
>>> line 2691, in configure_mappers
>>> mapper, mapper.class_)
>>>   File
>>> 
>>> "/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/event/attr.py",
>>> line 218, in __call__
>>> fn(*args, **kw)
>>>   File
>>> 
>>> "/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/orm/events.py",
>>> line 527, in wrap
>>> fn(*arg, **kw)
>>>   File "marshmallow_experiment.py", line 33, in print_stuff
>>> print getattr(class_, 'books')
>>> AttributeError: type object 'Author' has no attribute 'books'
>>> |
>>>
>>> Should not the backref be configured at that point? What I'm trying to 
>>> do
>>> is use the mapper_configured event in order to autocreate
>>> marshamallow-sqlalchemy schemas, which works fine except that because
>>> books doesn't exist at the point when the callback function runs, the
>>> resulting schema is also missing the books part.
>>>
>>> If I do this instead:
>>>
>>> |
>>> author = Author(name='Chuck Paluhniuk')
>>> print_stuff(None, Author)
>>> |
>>>
>>> Then the result is:
>>>
>>> |
>>> Author.books
>>> |
>> so you can see what's happening here.   Author.books is being set up, but
>> not within the event.  In this case Author is being configured before
>> Book, and as far as it knows, that's it, it's done.  The event is 
>> called. 
>> Book hasn't been touched so therefore neither has "books".   Only outside
>> of the whole thing, where Book also got set up, does your inspection 
>> work.
>>
>> The solution is to either use back_populates instead of backref, which is
>> probably the only way the ORM would have done it today if starting again,
>> or use the "after_configured()" event
>> 
>> http://docs.sqlalchemy.org/en/rel_1_0/orm/events.html#sqlalchemy.orm.events.MapperEvents.after_configured
>> 
>> 

Re: [sqlalchemy] mapper_configured event, class fully configured?

[Douglas Russell]

Ok, thanks, that makes sense.

Generally everything I see about SQLAlchemy referencing is using backref 
and it is convenient, but knowing that you actually think back_populates 
would be your preferred way to implement things is quite nice. I quite 
prefer that as I think it makes my code much more readable to have the 
relationship properties declared where they will exist.

Cheers,

Douglas

On Monday, 24 August 2015 21:54:17 UTC-4, Michael Bayer wrote:
>
>
>
> On 8/24/15 9:21 PM, Mike Bayer wrote:
>
>
>
> On 8/24/15 7:41 PM, Douglas Russell wrote:
>
>
> def print_stuff(mapper, class_):
> print getattr(class_, 'books')
>
> event.listen(mapper, 'mapper_configured', print_stuff)
>
> author = Author(name='Chuck Paluhniuk')
>
> When I run this code, the result is that when Author is first used, the 
> 'mapper_configured' event will fire and my print_stuff function callback 
> will run.
>
> The results is this:
>
> Traceback (most recent call last):
>   File "marshmallow_experiment.py", line 37, in 
> author = Author(name='Chuck Paluhniuk')
>   File "", line 2, in __init__
>   File 
> "/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/orm/instrumentation.py",
>  
> line 347, in _new_state_if_none
> state = self._state_constructor(instance, self)
>   File 
> "/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/util/langhelpers.py",
>  
> line 747, in __get__
> obj.__dict__[self.__name__] = result = self.fget(obj)
>   File 
> "/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/orm/instrumentation.py",
>  
> line 177, in _state_constructor
> self.dispatch.first_init(self, self.class_)
>   File 
> "/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/event/attr.py",
>  
> line 258, in __call__
> fn(*args, **kw)
>   File 
> "/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py",
>  
> line 2792, in _event_on_first_init
> configure_mappers()
>   File 
> "/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py",
>  
> line 2691, in configure_mappers
> mapper, mapper.class_)
>   File 
> "/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/event/attr.py",
>  
> line 218, in __call__
> fn(*args, **kw)
>   File 
> "/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/orm/events.py",
>  
> line 527, in wrap
> fn(*arg, **kw)
>   File "marshmallow_experiment.py", line 33, in print_stuff
> print getattr(class_, 'books')
> AttributeError: type object 'Author' has no attribute 'books'
>
> Should not the backref be configured at that point? What I'm trying to do 
> is use the mapper_configured event in order to autocreate 
> marshamallow-sqlalchemy schemas, which works fine except that because books 
> doesn't exist at the point when the callback function runs, the resulting 
> schema is also missing the books part.
>
> If I do this instead:
>
> author = Author(name='Chuck Paluhniuk')
> print_stuff(None, Author)
>
> Then the result is:
>
> Author.books
>
> so you can see what's happening here.   Author.books is being set up, but 
> not within the event.  In this case Author is being configured before Book, 
> and as far as it knows, that's it, it's done.  The event is called.  Book 
> hasn't been touched so therefore neither has "books".   Only outside of the 
> whole thing, where Book also got set up, does your inspection work.
>
> The solution is to either use back_populates instead of backref, which is 
> probably the only way the ORM would have done it today if starting again, 
> or use the "after_configured()" event 
> 
> http://docs.sqlalchemy.org/en/rel_1_0/orm/events.html#sqlalchemy.orm.events.MapperEvents.after_configured
>  
> which is intentionally here so that you can do things that require all 
> known mappers to be fully set up, which is the case here.
>
> As is so often the case I'm horrified the API docs don't have cross 
> linking here.   doing that..
>
> I've pushed up new descriptions and full cross-linking between 
> configure_mappers(), mapper_configured(), before_configured() and 
> after_configured(), for 0.9, 1.0, 1.1, master.  Should be up on the site in 
> a little while.
>

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Re: [sqlalchemy] mapper_configured event, class fully configured?

[Mike Bayer]

On 8/24/15 9:21 PM, Mike Bayer wrote:



On 8/24/15 7:41 PM, Douglas Russell wrote:


|
def print_stuff(mapper, class_):
print getattr(class_, 'books')

event.listen(mapper, 'mapper_configured', print_stuff)

author = Author(name='Chuck Paluhniuk')
|

When I run this code, the result is that when Author is first used, 
the 'mapper_configured' event will fire and my print_stuff function 
callback will run.


The results is this:

|
Traceback (most recent call last):
  File "marshmallow_experiment.py", line 37, in 
author = Author(name='Chuck Paluhniuk')
  File "", line 2, in __init__
  File 
"/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/orm/instrumentation.py", 
line 347, in _new_state_if_none

state = self._state_constructor(instance, self)
  File 
"/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/util/langhelpers.py", 
line 747, in __get__

obj.__dict__[self.__name__] = result = self.fget(obj)
  File 
"/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/orm/instrumentation.py", 
line 177, in _state_constructor

self.dispatch.first_init(self, self.class_)
  File 
"/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/event/attr.py", 
line 258, in __call__

fn(*args, **kw)
  File 
"/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py", 
line 2792, in _event_on_first_init

configure_mappers()
  File 
"/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py", 
line 2691, in configure_mappers

mapper, mapper.class_)
  File 
"/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/event/attr.py", 
line 218, in __call__

fn(*args, **kw)
  File 
"/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/orm/events.py", 
line 527, in wrap

fn(*arg, **kw)
  File "marshmallow_experiment.py", line 33, in print_stuff
print getattr(class_, 'books')
AttributeError: type object 'Author' has no attribute 'books'
|

Should not the backref be configured at that point? What I'm trying 
to do is use the mapper_configured event in order to autocreate 
marshamallow-sqlalchemy schemas, which works fine except that because 
books doesn't exist at the point when the callback function runs, the 
resulting schema is also missing the books part.


If I do this instead:

|
author = Author(name='Chuck Paluhniuk')
print_stuff(None, Author)
|

Then the result is:

|
Author.books
|
so you can see what's happening here.   Author.books is being set up, 
but not within the event.  In this case Author is being configured 
before Book, and as far as it knows, that's it, it's done.  The event 
is called.  Book hasn't been touched so therefore neither has 
"books".   Only outside of the whole thing, where Book also got set 
up, does your inspection work.


The solution is to either use back_populates instead of backref, which 
is probably the only way the ORM would have done it today if starting 
again, or use the "after_configured()" event 
http://docs.sqlalchemy.org/en/rel_1_0/orm/events.html#sqlalchemy.orm.events.MapperEvents.after_configured 
which is intentionally here so that you can do things that require all 
known mappers to be fully set up, which is the case here.


As is so often the case I'm horrified the API docs don't have cross 
linking here.   doing that..
I've pushed up new descriptions and full cross-linking between 
configure_mappers(), mapper_configured(), before_configured() and 
after_configured(), for 0.9, 1.0, 1.1, master.  Should be up on the site 
in a little while.


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Re: [sqlalchemy] mapper_configured event, class fully configured?

[Mike Bayer]

On 8/24/15 7:41 PM, Douglas Russell wrote:


|
def print_stuff(mapper, class_):
print getattr(class_, 'books')

event.listen(mapper, 'mapper_configured', print_stuff)

author = Author(name='Chuck Paluhniuk')
|

When I run this code, the result is that when Author is first used, 
the 'mapper_configured' event will fire and my print_stuff function 
callback will run.


The results is this:

|
Traceback (most recent call last):
  File "marshmallow_experiment.py", line 37, in 
author = Author(name='Chuck Paluhniuk')
  File "", line 2, in __init__
  File 
"/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/orm/instrumentation.py", 
line 347, in _new_state_if_none

state = self._state_constructor(instance, self)
  File 
"/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/util/langhelpers.py", 
line 747, in __get__

obj.__dict__[self.__name__] = result = self.fget(obj)
  File 
"/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/orm/instrumentation.py", 
line 177, in _state_constructor

self.dispatch.first_init(self, self.class_)
  File 
"/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/event/attr.py", 
line 258, in __call__

fn(*args, **kw)
  File 
"/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py", 
line 2792, in _event_on_first_init

configure_mappers()
  File 
"/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py", 
line 2691, in configure_mappers

mapper, mapper.class_)
  File 
"/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/event/attr.py", 
line 218, in __call__

fn(*args, **kw)
  File 
"/usr/local/Cellar/python/2.7.10/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sqlalchemy/orm/events.py", 
line 527, in wrap

fn(*arg, **kw)
  File "marshmallow_experiment.py", line 33, in print_stuff
print getattr(class_, 'books')
AttributeError: type object 'Author' has no attribute 'books'
|

Should not the backref be configured at that point? What I'm trying to 
do is use the mapper_configured event in order to autocreate 
marshamallow-sqlalchemy schemas, which works fine except that because 
books doesn't exist at the point when the callback function runs, the 
resulting schema is also missing the books part.


If I do this instead:

|
author = Author(name='Chuck Paluhniuk')
print_stuff(None, Author)
|

Then the result is:

|
Author.books
|
so you can see what's happening here.   Author.books is being set up, 
but not within the event.  In this case Author is being configured 
before Book, and as far as it knows, that's it, it's done.  The event is 
called.  Book hasn't been touched so therefore neither has "books".   
Only outside of the whole thing, where Book also got set up, does your 
inspection work.


The solution is to either use back_populates instead of backref, which 
is probably the only way the ORM would have done it today if starting 
again, or use the "after_configured()" event 
http://docs.sqlalchemy.org/en/rel_1_0/orm/events.html#sqlalchemy.orm.events.MapperEvents.after_configured 
which is intentionally here so that you can do things that require all 
known mappers to be fully set up, which is the case here.


As is so often the case I'm horrified the API docs don't have cross 
linking here.   doing that..




I.e. It is now there.

Thanks again for your continued excellent support.

Douglas
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