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PODjango custom unique together constraint
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  1. PODjango custom unique together constraint
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    copied!<p>I have a users share model something like below:</p> <pre><code>class Share( models.Model ): sharer = models.ForeignKey(User, verbose_name=_("Sharer"), related_name='sharer') receiver = models.ForeignKey(User, verbose_name=_("Receiver"), related_name='receiver') class Meta: unique_together = ( ("sharer", "receiver"), ("receiver", "sharer") ) </code></pre> <p>I want to save a single object for sharer(S) and receiver(R) (order doesn't matters R-S or S-R). but above unique_together will not fulfil this; Suppose R-S is in database and then if I save S-R I will not get validation for this. For this I have written custom unique validation for Share model.</p> <pre><code> def validate_unique( self, *args, **kwargs): super(Share, self).validate_unique(*args, **kwargs) if self.__class__.objects.filter( Q(sharer=self.receiver, receiver=self.sharer) ).exists(): raise ValidationError( { NON_FIELD_ERRORS: ('Share with same sharer and receiver already exists.',) } ) def save(self, *args, **kwargs): # custom unique validate self.validate_unique() super(Share, self).save(*args, **kwargs) </code></pre> <p>This method works fine in normal use.</p> <p><strong>Problem:</strong> I have an matching algorithm which gets a share's and a receiver's requests and saves Share object(either S-R or R-S) then send them response(share object) <strong><em>at almost same time</em></strong>. As I am checking duplication with query(no database level) it takes time, so at the end I have 2 Objects S-R and R-S.</p> <p>I want some solution for this that for a sharer S and a receiver R I can only save single share object, either S-R or R-S else get some validation error(like IntegrityError of databse).</p> <p>Django=1.4, Database=Postgresql</p>
 

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