class MyModelForm(SAModelForm):
    class Meta:
        model = MyModel
        mapping = {
            'field1': 'instance.child.attribute',
            'field2': 'attribute3',
        }
    field1 = forms.IntegerField()
    field2 = forms.CharField()

class MyForm(Form, FieldAccessMixin):
    class Meta:
        access = {
            ('field1', 'field2'): access_admin,
            'field3': MyForm.access_admin1,
            None: lambda user, instance: FieldAccess.enabled,
        }
    field1 = forms.IntegerField()

    @classmethod
    def access_admin1(cls):
        return FieldAccess.readonly

def access_bank_details(user, instance):
    if not has_perm(user, instance, 'edit_bank_account'):
        if has_perm(user, instance, 'edit_contract_id'):
            return FieldAccess.readonly
        return FieldAccess.excluded
    return FieldAccess.enabled

def access_contract_id(user, instance):
    if not (has_perm(user, instance, 'edit_contract_id') and has_perm(user, instance, 'do_stuff')):
            return FieldAccess.readonly

class BankForm(Form, FieldAccessMixin):
    class Meta:
        access = {
            ('bank_account', 'bank_name', 'bank_balance'): access_bank_details,
            'contract_id': access_contract_id,
            None: BankForm.access_check,
        }

    bank_account = forms.CharField()
    bank_name = forms.CharField()
    bank_balance = forms.FloatField()

    contract_id = forms.IntegerField()

    some_other_field = forms.CharField()

    @classmethod
    def access_check(cls):
        return FieldAccess.readonly

@access_filter
def can_view_event(user, instance):
    if user.has_perm('event', 'view'):
        return FieldAccess.enabled

@access_filter
def can_view_merchant(user, instance):
    if user.has_perm('merchant', 'view'):
        return FieldAccess.enabled

@access_filter
def exclude_for_not_finance(user, instance):
    if not user.has_perm('merchant', 'some_financial_permission'):
        return FieldAccess.excluded

...

    access = {
        # Filters are applied left to right, the result is the first filter to return a FieldAccess value

        # This will be enabled if you can view the event, else readonly
        'field_a': can_view_event | default(FieldAccess.readonly),

        # This will be enabled if you can view the event OR the merchant, else excluded
        'field_b': can_view_event | can_view_merchant | default(FieldAccess.excluded),

        # This will be enabled if you can view the event AND the merchant, else excluded
        'field_b2': can_view_event & can_view_merchant | default(FieldAccess.excluded),

        # This will be excluded if you don't have some finance permission, else enabled (this is the default)
        'field_c': exclude_for_not_finance
    }