Possibility to preserve skipped attributes on reify

[McRip]

Hello, i added the possibility to preserve skipped attributes on reify instead of setting them all to nil.
I added an option to the reify method to enable this behaviour. A Test is attached to this PR.

Thanks for merging.

[McRip]

I actually have no clue why this fails:

1. JsonVersion Methods Class #where_object_changes valid arguments should be able to locate versions according to their object_changes contents
   Failure/Error: expect(fruit.versions.where_object_changes(:color => color)).to eq(fruit.versions[1..2])

   expected: [#<JsonVersion id: 5, item_type: "Fruit", item_id: 2, event: "update", whodunnit: nil, object: {"id"=>2, "name"=>"pomegranate", "color"=>nil}, object_changes: {"name"=>["pomegranate", "coconut"], "color"=>[nil, "navy"]}, created_at: "2015-07-31 09:23:59">, #<JsonVersion id: 6, item_type: "Fruit", item_id: 2, event: "update", whodunnit: nil, object: {"id"=>2, "name"=>"coconut", "color"=>"navy"}, object_changes: {"name"=>["coconut", "orange"]}, created_at: "2015-07-31 09:23:59">]
        got: #<ActiveRecord::AssociationRelation [#<JsonVersion id: 5, item_type: "Fruit", item_id: 2, event: "update", whodunnit: nil, object: {"id"=>2, "name"=>"pomegranate", "color"=>nil}, object_changes: {"name"=>["pomegranate", "coconut"], "color"=>[nil, "navy"]}, created_at: "2015-07-31 09:23:59">]>

   (compared using ==)

   Diff:
   @@ -1,4 +1,4 @@
   -[#<JsonVersion:0x575ddcc9
   +[#<JsonVersion:0x288bd61a
      id: 5,
      item_type: "Fruit",
      item_id: 2,
   @@ -6,14 +6,5 @@
      whodunnit: nil,
      object: {"id"=>2, "name"=>"pomegranate", "color"=>nil},
      object_changes: {"name"=>["pomegranate", "coconut"], "color"=>[nil, "navy"]},
   -  created_at: Fri, 31 Jul 2015 09:23:59 UTC +00:00>,
   - #<JsonVersion:0x379f2abf
   -  id: 6,
   -  item_type: "Fruit",
   -  item_id: 2,
   -  event: "update",
   -  whodunnit: nil,
   -  object: {"id"=>2, "name"=>"coconut", "color"=>"navy"},
   -  object_changes: {"name"=>["coconut", "orange"]},
      created_at: Fri, 31 Jul 2015 09:23:59 UTC +00:00>]
 # ./spec/models/json_version_spec.rb:67:in `(root)'

[jaredbeck]

Don't worry about the JsonVersion test, it's flakey. I ran it again and it passed.

[jaredbeck]

Can you squash this into one commit, please?

[jaredbeck]

Why did the force option change from true to :cascade on every table? Is that the new recommended value, or is it something you did intentionally? From the docs:

:force
Set to true to drop the table before creating it. Set to :cascade to drop 
dependent objects as well. Defaults to false.

It seems like with force: true the order of table creation wouldn't matter, but with :cascade it would, so true seems preferable to me.

[McRip]

It was changed during db:migrate. This has changed since Rails 4.2. The release notes say:

SchemaDumper uses force: :cascade on create_table. This makes it possible to reload a schema when foreign keys are in place.

[jaredbeck]

This seems like a useful feature, and it doesn't increase the complexity of reify too much.

Also, I like this as an option to reify, as opposed to e.g. model-specific config.

As far as the API is concerned, you have:

+    # :preserve             `false` default behaviour
+    #                       `true` preserve attributes of reified object instead of setting 
+    #                       unknown attributes to nil

but I think I'd prefer something like:

+    # :unversioned_attribute    `:nil` - (default) attributes undefined in version record 
+    #                           are set to nil in reified record
+    #                           `:preserve` - attributes undefined in version record are 
+    #                           not modified

My thinking is, this allows for a third option in the future.

[McRip]

Hello Jared,
thanks for your feedback. I changed the syntax and merged all the commits into one.

[jaredbeck]

Merged. Thanks Moritz!