Fixed #3232 -- newforms: Added save_instance(), which saves a given bound form's clean_data into a given model instance with the same field names

git-svn-id: http://code.djangoproject.com/svn/django/trunk@4300 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/newforms/models.py

@@ -5,7 +5,7 @@ and database field objects.
 
 from forms import BaseForm, DeclarativeFieldsMetaclass, SortedDictFromList
 
-__all__ = ('form_for_model', 'form_for_instance', 'form_for_fields')
+__all__ = ('save_instance', 'form_for_model', 'form_for_instance', 'form_for_fields')
 
 def model_save(self, commit=True):
     """
@@ -20,13 +20,19 @@ def model_save(self, commit=True):
         obj.save()
     return obj
 
-def make_instance_save(opts, instance):
-    "Returns the save() method for a form_for_instance Form."
+def save_instance(form, instance, commit=True):
+    """
+    Saves bound Form ``form``'s clean_data into model instance ``instance``.
+
+    Assumes ``form`` has a field for every non-AutoField database field in
+    ``instance``. If commit=True, then the changes to ``instance`` will be
+    saved to the database. Returns ``instance``.
+    """
     from django.db import models
-    def apply_changes(self, commit=True):
-        if self.errors:
+    opts = instance.__class__._meta
+    if form.errors:
         raise ValueError("The %s could not be changed because the data didn't validate." % opts.object_name)
-        clean_data = self.clean_data
+    clean_data = form.clean_data
     for f in opts.fields + opts.many_to_many:
         if isinstance(f, models.AutoField):
             continue
@@ -34,13 +40,18 @@ def make_instance_save(opts, instance):
     if commit:
         instance.save()
     return instance
-    return apply_changes
+
+def make_instance_save(instance):
+    "Returns the save() method for a form_for_instance Form."
+    def save(self, commit=True):
+        return save_instance(self, instance, commit)
+    return save
 
 def form_for_model(model, form=BaseForm):
     """
     Returns a Form class for the given Django model class.
 
-    Provide 'form' if you want to use a custom BaseForm subclass.
+    Provide ``form`` if you want to use a custom BaseForm subclass.
     """
     opts = model._meta
     field_list = []
@@ -55,7 +66,7 @@ def form_for_instance(instance, form=BaseForm):
     """
     Returns a Form class for the given Django model instance.
 
-    Provide 'form' if you want to use a custom BaseForm subclass.
+    Provide ``form`` if you want to use a custom BaseForm subclass.
     """
     model = instance.__class__
     opts = model._meta
@@ -67,7 +78,7 @@ def form_for_instance(instance, form=BaseForm):
             field_list.append((f.name, formfield))
     fields = SortedDictFromList(field_list)
     return type(opts.object_name + 'InstanceForm', (form,),
-        {'fields': fields, '_model': model, 'save': make_instance_save(opts, instance)})
+        {'fields': fields, '_model': model, 'save': make_instance_save(instance)})
 
 def form_for_fields(field_list):
     "Returns a Form class for the given list of Django database field instances."

tests/modeltests/model_forms/models.py

@@ -15,9 +15,11 @@ database.
 The function django.newforms.form_for_instance() takes a model instance and
 returns a Form that is tied to the instance. This form works just like any
 other Form, with one additional method: save(). The save()
-method updates the model instance. It saves the changes to the database if
-save(commit=True), which is default. If you pass commit=False, then you'll
-get the object without committing the changes to the database.
+method updates the model instance. It also takes a commit=True parameter.
+
+The function django.newforms.save_instance() takes a bound form instance and a
+model instance and saves the form's clean_data into the instance. It also takes
+a commit=True parameter.
 """
 
 from django.db import models
@@ -45,7 +47,7 @@ class Article(models.Model):
         return self.headline
 
 __test__ = {'API_TESTS': """
->>> from django.newforms import form_for_model, form_for_instance, BaseForm
+>>> from django.newforms import form_for_model, form_for_instance, save_instance, BaseForm, Form, CharField
 >>> import datetime
 
 >>> Category.objects.all()
@@ -218,4 +220,20 @@ Add some categories and test the many-to-many form output.
 <option value="3">Third test</option>
 </select></li>
 
+Here, we define a custom Form. Because it happens to have the same fields as
+the Category model, we can use save_instance() to apply its changes to an
+existing Category instance.
+>>> class ShortCategory(Form):
+...     name = CharField(max_length=5)
+...     url = CharField(max_length=3)
+>>> cat = Category.objects.get(name='Third test')
+>>> cat
+<Category: Third test>
+>>> cat.id
+3
+>>> sc = ShortCategory({'name': 'Third', 'url': '3rd'})
+>>> save_instance(sc, cat)
+<Category: Third>
+>>> Category.objects.get(id=3)
+<Category: Third>
 """}