python - Checking uniqueness contraint during form validation in App Engine -

i using flask , wtforms in app engine, trying implement uniqueness contraint on 1 of field. question big, please patient , have been stuck here many hours, need people. started learning app engine, flask , wtforms month ago. in advance.

application has model 'team' shown below:

class team(db.model):     name = db.stringproperty(required=true)     -- other fields here -- 

requirement: name of team has unique.

i have followed links

• http://www.codigomanso.com/en/2010/09/solved-anadir-claves-unicas-en-google-app-engine-en-3-lineas/
• http://squeeville.com/2009/01/30/add-a-unique-constraint-to-google-app-engine/
• http://csimms.botonomy.com/2012/07/there-are-only-two-ways-to-enforce-unique-constraints-in-google-app-engine.html

have come following code:

models.py: created separate table 'unique' given in link:

class unique(db.model):  """ handles uniqueness constriant on field """  @classmethod def unique_check(cls, form_name, field_data):     def tx(form_name, field_data):         key_name = "%s%s" % (form_name, field_data)         uk = unique.get_by_key_name(key_name)         app.logger.debug("uk:" + str(uk))         if uk:             return false         uk = unique(key_name=key_name)         uk.put()         return true     ret_val = db.run_in_transaction(tx, form_name, field_data)     app.logger.debug("ret_val:" + str(ret_val))     return ret_val 

forms.py: have overridden __init__() , validate_on_submit() function in uniqueness checked , if not unique, error attached field , validation error raised in same way wtforms's validators.

class teamform(wtf.form):  def __init__(self, *args, **kwargs):     super(teamform, self).__init__(*args, **kwargs)     if kwargs.get('edit', none):         self.old_name = self.name.data.lower()  def validate_on_submit(self, edit=false):     if not super(teamform, self).validate_on_submit():         return false     if edit:         if self.old_name , self.old_name != self.name.data.lower():             unique.delete_entity(self.__class__.__name__, self.old_name)             if not unique.unique_check(self.__class__.__name__, self.name.data.lower()):                 self.name.errors.append("value '%s' not unique" % self.name.data)         return false     else:         if not unique.unique_check(self.__class__.__name__, self.name.data.lower()):             self.name.errors.append("value '%s' not unique" % self.name.data)             return false      return true      **----  form fields declaration ----** 

the above code works when new team inserted.i mean checks uniqueness properly. problem occurs, when user edits team information. following 2 scenarios problematic:

• when user tries submit form, application throw "not unique" error, obvious because "unique" table has "key_name" team.
• if user changes "team name", application has delete previous team name "unique" table , has check uniqueness "changed team name". not able handle these 2 scenarios.

my edit_team function looks this:

@app.route('/team/edit/<key>', methods=['get','post']) @login_required def edit_team(key):      k = db.key(key)     team = db.get(k)     form = teamform(obj = team, edit=true) # save old name, doesn't work.     if form.validate_on_submit(edit=true): # edit=true given in edit function         team.name = form.name.data         -- others fields updated in similar way --         team.put()         return redirect(url_for('teams_list'))     return render_template('edit_team.html', form=form) 

problem can solved if able find out 'old name' of team, can delete "unique" table. can see saving old name of team in teamform __init__() function, __init__() called during get(old name saved) , in post(modified name saved!!). so, cannot find out old name @ , remains in "unique" table, nobody can use "old team name" anymore.

i tried explain as possible, please let me know if want more info.

edit: didn't answer question first time.

separate instances of form object instantiated , post requests, can't save old_name self.

you'll need pass old_name browser in form, , have browser submit old_name in post request.

the easyish way create hidden form field user doesn't see, submitted post request. i'm not familiar wtforms assume can initialize old_name field value in request handler.