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Update diffing section of README.

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Andy Stewart 2011-07-13 10:21:49 +01:00
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@ -453,11 +453,20 @@ Remember to add those extra columns to your `versions` table ;)
## Diffing Versions
When you're storing every version of an object, as PaperTrail lets you do, you're almost certainly going to want to diff those versions against each other. However I haven't built a diff method into PaperTrail because I think diffing is best left to dedicated libraries, and also it's hard to come up with a diff method to suit all the use cases.
There are two scenarios: diffing adjacent versions and diffing non-adjacent versions.
You might be surprised that PaperTrail doesn't use diffs internally anyway. When I designed PaperTrail I wanted simplicity and robustness so I decided to make each version of an object self-contained. A version stores all of its object's data, not a diff from the previous version.
The best way to diff adjacent versions is to get PaperTrail to do it for you. If you add an `object_changes` text column to your `versions` table, either at installation time with the `--with-changes` option or manually, PaperTrail will store the `changes` diff in each `update` version. You can use the `version.changeset` method to retrieve it. For example:
So instead here are some specialised diffing libraries which you can use on top of PaperTrail.
>> widget = Widget.create :name => 'Bob'
>> widget.versions.last.changeset # nil
>> widget.update_attributes :name => 'Robert'
>> widget.versions.last.changeset # {'name' => ['Bob', 'Robert']}
Note PaperTrail only stores the changes for updates; there's no point storing them for created or destroyed objects.
Please be aware that PaperTrail doesn't use diffs internally. When I designed PaperTrail I wanted simplicity and robustness so I decided to make each version of an object self-contained. A version stores all of its object's data, not a diff from the previous version. This means you can delete any version without affecting any other.
To diff non-adjacent versions you'll have to write your own code. These libraries may help:
For diffing two strings: