Commits on Nov 6, 2018

1. Fix handling of duplicates for replace on has_many-through …

   There was a bug in the handling of duplicates when
   assigning (replacing) associated records, which made the result
   dependent on whether a given record was associated already before
   being assigned anew. E.g.
   
       post.people = [person, person]
       post.people.count
       # => 2
   
   while
   
       post.people = [person]
       post.people = [person, person]
       post.people.count
       # => 1
   
   This change adds a test to provoke the former incorrect behavior, and
   fixes it.
   
   Cause of the bug was the handling of record collections as sets, and
   using `-` (difference) and `&` (union) operations on them
   indiscriminately. This temporary conversion to sets would eliminate
   duplicates.
   
   The fix is to decorate record collections for these operations, and
   only for the `has_many :through` case. It is done by counting
   occurrences, and use the record together with the occurrence number as
   element, in order to make them work well in sets. Given
   
       a, b = *Person.all
   
   then the collection used for finding the difference or union of
   records would be internally changed from
   
        [a, b, a]
   
   to
   
        [[a, 1], [b, 1], [a, 2]]
   
   for these operations. So a first occurrence and a second occurrence
   would be distinguishable, which is all that is necessary for this
   task.
   
   Fixes rails#33942.

   

   febeling committed Nov 6, 2018
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   8104589 View commit details

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2. Rename union to intersection

   

   febeling committed Nov 6, 2018
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   11bad94 View commit details

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3. Optimize difference and intersection

   

   febeling committed Nov 6, 2018
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   f915758 View commit details

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