issue2551120 - The sorted method of MultilinkHTMLProperty crashes ...

if the given property is unset for an element of the list.

Crash fixed. New feature NoneFirst added to method to make unset values
sort at start or end of sorted list.

Current testing framework for this code is insuffient for testing
change. Committing without automated test because it solves a crash.

Author: rouilj

CHANGES.txt

@@ -98,7 +98,11 @@ Fixed:
 - issue2551078 - Fix traceback caused when putting two id's into a
   Link html field. A ValueError is raised. Handle exception and return
   value. hyperdb.py now reports 'you may only enter ID values for
-  property ...' to the user.
+  property ...' to the user. (John Rouillard)
+- issue2551120 - The sorted method of MultilinkHTMLProperty crashes,
+  if the given property is unset for an element of the list. Crash
+  fixed. New feature NoneFirst added to method to make unset values
+  sort at start or end of sorted list. (John Rouillard)
 
 Features:
 - issue2550522 - Add 'filter' command to command-line

doc/customizing.txt

@@ -3292,7 +3292,17 @@ sorted      only on Multilink properties - produce a list of the linked
                python:context.files.sorted('creation', reverse=True)
 
             Will list the files by upload date in reverse order from
-            the prior example.
+            the prior example. If the property can be unset, you can
+            use the ``NoneFirst`` parameter to sort the None/Unset
+            values at the front or the end of the list. For example::
+            
+                python:context.files.sorted('creation', NoneFirst=True)
+            
+            will sort files by creation date with files missing a
+            creation date at the start of the list. The default for
+            ``NoneFirst`` is False so these files will sort at the end
+            by default. (Note creation date is never unset, but you
+            get the idea.) 
 reverse     only on Multilink properties - produce a list of the linked
             items in reverse order
 isset       returns True if the property has been set to a value

roundup/cgi/templating.py

@@ -2612,10 +2612,32 @@ def reverse(self):
         l.reverse()
         return self.viewableGenerator(l)
 
-    def sorted(self, property, reverse=False):
-        """ Return this multilink sorted by the given property """
+    def sorted(self, property, reverse=False, NoneFirst=False):
+        """ Return this multilink sorted by the given property 
+
+            Set Nonefirst to True to sort None/unset property
+            before a property with a valid value.
+            
+        """
+
+        # use 2 if NoneFirst is False to sort None last
+        # 0 to sort to sort None first
+        # 1 is used to sort the integer values.
+        NoneCode = (2,0)[NoneFirst]
+        def keyfunc(v):
+            # Return tuples made of (group order (int), base python
+            # type) to sort function.
+            # Do not return v[property] as that returns an HTMLProperty
+            # type/subtype that throws an exception when sorting
+            # python type (int. str ...) against None.
+            val = v[property]._value
+            if val:
+                return (1, val)  # val should be base python type
+            elif val is None:
+                return (NoneCode, None)
+
         value = list(self.__iter__())
-        value.sort(key=lambda a:a[property], reverse=reverse)
+        value.sort(key=keyfunc, reverse=reverse)
         return value
 
     def __contains__(self, value):