Fix and test handling of missing terms in collections.

CHANGES.txt

@@ -5,7 +5,8 @@ CHANGES
 3.3.1 (unreleased)
 ------------------
 
-- Nothing changed yet.
+- Fix handling of missing terms in collections. (See version 2.9 describing
+  this feature.)
 
 
 3.3.0 (2016-03-09)

src/z3c/form/term.py

@@ -266,7 +266,35 @@ def __init__(self, context, request, form, field, vocabulary, widget):
         self.terms = vocabulary
 
 
-class MissingCollectionTermsVocabulary(MissingTermsMixin,
+class MissingCollectionTermsMixin(MissingTermsMixin):
+    """`MissingTermsMixin` adapted to collections."""
+
+    def getTerm(self, value):
+        try:
+            return super(MissingCollectionTermsMixin, self).getTerm(value)
+        except LookupError:
+            if self._canQueryCurrentValue():
+                if value in self._queryCurrentValue():
+                    return self._makeMissingTerm(value)
+            raise
+
+    def getTermByToken(self, token):
+        try:
+            return super(
+                MissingCollectionTermsMixin, self).getTermByToken(token)
+        except LookupError:
+            if self._canQueryCurrentValue():
+                for value in self._queryCurrentValue():
+                    term = self._makeMissingTerm(value)
+                    if term.token == token:
+                        # check if the given token matches the value, if not
+                        # fall back on LookupError, otherwise we might accept
+                        # any crap coming from the request
+                        return term
+            raise LookupError(token)
+
+
+class MissingCollectionTermsVocabulary(MissingCollectionTermsMixin,
                                        CollectionTermsVocabulary):
     """ITerms adapter for zope.schema.ICollection based implementations using
     vocabulary with missing terms support."""
@@ -286,6 +314,7 @@ class CollectionTermsSource(SourceTerms):
         interfaces.IWidget)
 
 
-class MissingCollectionTermsSource(MissingTermsMixin, CollectionTermsSource):
+class MissingCollectionTermsSource(MissingCollectionTermsMixin,
+                                   CollectionTermsSource):
     """ITerms adapter for zope.schema.ICollection based implementations using
     source with missing terms support."""

src/z3c/form/term.txt

@@ -529,3 +529,92 @@ Finally, there are terms adapters for all collections:
   ...     rating_context, request, None, contextualSourceRatingsField, widget)
   >>> [entry.title for entry in terms]
   [u'ugly', u'nice', u'great']
+
+
+Missing terms in collections
+############################
+
+Sometimes it happens that a value goes away from the source, but our
+stored collection still has this value.
+
+  >>> zope.component.provideAdapter(term.MissingCollectionTermsSource)
+
+  >>> terms = term.CollectionTerms(
+  ...     RatingContext(), request, None, contextualSourceRatingsField, widget)
+  >>> terms
+  <z3c.form.term.MissingCollectionTermsSource object at 0x...>
+  >>> terms.getTermByToken('42')
+  Traceback (most recent call last):
+  ...
+  LookupError: 42
+
+The same goes with looking up a term by value:
+
+  >>> terms.getTerm(42)
+  Traceback (most recent call last):
+  ...
+  LookupError: 42
+
+Ooops, well this works only if the context has the right value for us.
+This is because we don't want to accept any crap that's coming from HTML.
+
+  >>> class IRatings(zope.interface.Interface):
+  ...     ratings = zope.schema.List(
+  ...         title=u'Contextual Sourced Ratings',
+  ...         value_type=contextualSourceRatingField)
+  >>> @zope.interface.implementer(IRatings)
+  ... class Ratings(object):
+  ...     ratings = None
+  ...     base_value = 10
+
+  >>> ctx = Ratings()
+  >>> ctx.ratings = [42, 10]
+
+  >>> ratingsWidget = z3c.form.widget.Widget(request)
+  >>> ratingsWidget.context = ctx
+  >>> from z3c.form import interfaces
+  >>> zope.interface.alsoProvides(ratingsWidget, interfaces.IContextAware)
+  >>> from z3c.form.datamanager import AttributeField
+  >>> zope.component.provideAdapter(AttributeField)
+
+  >>> terms = term.CollectionTerms(
+  ...     ctx, request, None, IRatings['ratings'], ratingsWidget)
+
+Here we go:
+
+  >>> term = terms.getTerm(42)
+  >>> missingTerm = terms.getTermByToken('42')
+
+We get the term, we passed the token, the value is coming from the context.
+
+  >>> missingTerm.token
+  '42'
+  >>> missingTerm.value
+  42
+
+We cannot figure the title, so we construct one.
+Override ``makeMissingTerm`` if you want your own.
+
+  >>> missingTerm.title
+  u'Missing: ${value}'
+
+Still we raise LookupError if the token does not fit the context's value:
+
+  >>> missingTerm = terms.getTermByToken('99')
+  Traceback (most recent call last):
+  ...
+  LookupError: 99
+
+The same goes with looking up a term by value.
+We get the term if the context's value fits:
+
+  >>> missingTerm = terms.getTerm(42)
+  >>> missingTerm.token
+  '42'
+
+And an exception if it does not:
+
+  >>> missingTerm = terms.getTerm(99)
+  Traceback (most recent call last):
+  ...
+  LookupError: 99