class NewsItemAdmin(admin.ModelAdmin):

    def save_model(self, request, obj, form, change):
        user_company_list = request.user.companies.values_list('id', flat=True)
        #import ipdb; ipdb.set_trace()
        obj.companies = user_company_list
        obj.content = 'dummy text'
        change = True
        super(NewsItemAdmin, self).save_model(request, obj, form, change)