Django filter the queryset of ModelChoiceField - what did i do wrong? -

i know many questions exist same topic, confused on 1 point. intent show 2 modelchoicefields on form, not directly tie them game model.

i have following:

forms.py

class addgame(forms.modelform):     won_lag = forms.choicefield(choices=[('1','home') , ('2', 'away') ])     home_team = forms.modelchoicefield(queryset=player.objects.all())     away_team = forms.modelchoicefield(queryset=player.objects.all())      class meta:         model = game         fields = ('match', 'match_sequence') 

views.py

def game_add(request, match_id):     game = game()     try:         match = match.objects.get(id=match_id)     except match.doesnotexist:         # have no object!          pass      game.match = match      # form     form = addgame(request.post or none, instance=game)     form.fields['home_team'].queryset = player.objects.filter(team=match.home_team )      # handle post-back (new or existing; on success nav game list)     if request.method == 'post':         if form.is_valid():             form.save()             # redirect list of games specified match             return httpresponseredirect(reverse('nine.views.list_games'))      ... 

where confused when setting queryset filter. first tried:

form.home_team.queryset = player.objects.filter(team=match.home_team ) 

but got error

attributeerror @ /nine/games/new/1  'addgame' object has no attribute 'home_team' ... 

so changed following: (after reading other posts)

form.fields['home_team'].queryset = player.objects.filter(team=match.home_team ) 

and works fine.

so question is, difference between 2 lines? why did second 1 work , not first? sure newbie (i one) question, baffled.

any appreciated.

django forms metaclasses:

>>> type(addgame) <class 'django.forms.forms.declarativefieldsmetaclass'> 

they create form instance according information given in definition. means, won't see when define addgame form. when instantiate it, metaclass return proper instance fields provided:

>>> type(addgame()) <class 'your_app.forms.addgame'> 

so, instance, can access fields doing form.field. in fact, bit more complicated that. there 2 types of fields can access. form['field'] you'll accessing boundfield. used output , raw_input.

by doing form.fields['fields'] you'll accessing field python can understand. because if got input, there's validation , data conversion take places (in fact, fields used this, the general process of validation bit more complicated).

i hope might clear little issue may see, whole form's api big , complicated. simple end-users has lot of programming behind curtains :)

reading links provides clear doubts , improve knowledge useful topic , django in general.

good luck!

update: way, if want learn more python's metaclasses, this hell of answer topic.