feature discussion: before_exec() Instance event - sqlalchemy-devel

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Message from discussion feature discussion: before_exec() Instance event
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Date: Tue, 13 Mar 2012 18:10:03 -0400
From: Randy Syring <rsyr...@gmail.com>
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Subject: feature discussion: before_exec() Instance event
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I'm wondering what the chances are of getting some kind of instance 
event that would send INSERT/UPDATE values back to it right before 
sess.exec() is called for an INSERT or UPDATE operation.  I'd imagine 
something like:

@event.listen_for(Car, 'before_exec'):
def validate_entity(car, values, type):
     assert type in ('insert', 'update')
     if 'active_flag' in values:
         values['active_flag'] = 1 if values['active_flag'] else 0
     if values['make'] not in ('Ford', 'Chevy'):
         raise ValueError('make not recognized')
     if 'mileage' not in values:
         values['mileage'] = 'unknown'
     return values

I currently have a validation library 
(https://bitbucket.org/rsyring/sqlalchemy-validation/) that uses the 
before_flush session event to try and do validation, but I run into 
problems with validating values that come from column defaults and other 
more "low level" places.

I realize there are different ways to do validation and there are 
arguments to be made against ever needing to validate a default value.  
However, I'd like to be able to do validation of an entity in as 
low-level of a place as possible so as to guarauntee catching as many 
exceptions as I can without relying on form libraries to do input 
validation on my model.  I want the model to be self-validating so that 
I can use it in a web application, GUI, or console app and not have to 
write validation code in three places.

If this is possible, I'm willing to work on providing a patch.  I just 
want to make sure its possible and would be considered for acceptance 
before I go down that route.

Thanks.

---------------------------------------------
Randy Syring
Development&  Executive Director
Level 12 Technologies  <https://www.lev12.com/>  (formerly Intelicom)
Direct: 502-276-0459
Office: 502-212-9913

Intelicom is now Level 12 Technologies,learn more about our name change  <https://www.lev12.com/our-history>.
Please update your address book with my new email address.

Principled People, Technology that Works


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    I'm wondering what the chances are of getting some kind of instance
    event that would send INSERT/UPDATE values back to it right before
    sess.exec() is called for an INSERT or UPDATE operation.Â  I'd
    imagine something like:<br>
    <br>
    <tt>@event.listen_for(Car, 'before_exec'):<br>
      def validate_entity(car, values, type):<br>
      Â Â Â  assert type in ('insert', 'update')<br>
      Â Â Â  if 'active_flag' in values:<br>
      Â Â Â Â Â Â Â  values['active_flag'] = 1 if values['active_flag'] else 0<br>
      Â Â Â  if values['make'] not in ('Ford', 'Chevy'):<br>
      Â Â Â Â Â Â Â  raise ValueError('make not recognized')<br>
      Â Â Â  if 'mileage' not in values:<br>
      Â Â Â Â Â Â Â  values['mileage'] = 'unknown'<br>
      Â Â Â  return values</tt><br>
    <br>
    I currently have a validation library
    (<a class="moz-txt-link-freetext" href="https://bitbucket.org/rsyring/sqlalchemy-validation/">https://bitbucket.org/rsyring/sqlalchemy-validation/</a>) that uses the
    before_flush session event to try and do validation, but I run into
    problems with validating values that come from column defaults and
    other more "low level" places.Â  <br>
    <br>
    I realize there are different ways to do validation and there are
    arguments to be made against ever needing to validate a default
    value.Â  However, I'd like to be able to do validation of an entity
    in as low-level of a place as possible so as to guarauntee catching
    as many exceptions as I can without relying on form libraries to do
    input validation on my model.Â  I want the model to be
    self-validating so that I can use it in a web application, GUI, or
    console app and not have to write validation code in three places.<br>
    <br>
    If this is possible, I'm willing to work on providing a patch.Â  I
    just want to make sure its possible and would be considered for
    acceptance before I go down that route.<br>
    <br>
    Thanks.<br>
    <div class="moz-signature">
      <pre>---------------------------------------------
Randy Syring
Development &amp; Executive Director
<a href="https://www.lev12.com/">Level 12 Technologies</a> (formerly Intelicom)
Direct: 502-276-0459
Office: 502-212-9913

Intelicom is now Level 12 Technologies, <a href="https://www.lev12.com/our-history">learn more about our name change</a>.
Please update your address book with my new email address.

Principled People, Technology that Works
</pre>
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