回答編集履歴
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追記
test
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@@ -35,3 +35,119 @@
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end
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```
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ソースコードから一部抜粋
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```rb
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# Change the name:
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#
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# person.name = 'Bob'
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# person.changed? # => true
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# person.name_changed? # => true
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# person.name_changed?(from: nil, to: "Bob") # => true
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# person.name_was # => nil
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# person.name_change # => [nil, "Bob"]
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# person.name = 'Bill'
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# person.name_change # => [nil, "Bill"]
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#
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# Save the changes:
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#
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# person.save
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# person.changed? # => false
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# person.name_changed? # => false
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#
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# Reset the changes:
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#
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# person.previous_changes # => {"name" => [nil, "Bill"]}
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# person.name_previously_changed? # => true
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# person.name_previous_change # => [nil, "Bill"]
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# person.reload!
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# person.previous_changes # => {}
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#
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# Rollback the changes:
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#
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# person.name = "Uncle Bob"
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# person.rollback!
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# person.name # => "Bill"
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# person.name_changed? # => false
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#
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# Assigning the same value leaves the attribute unchanged:
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#
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# person.name = 'Bill'
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# person.name_changed? # => false
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# person.name_change # => nil
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#
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# Which attributes have changed?
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#
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# person.name = 'Bob'
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# person.changed # => ["name"]
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# person.changes # => {"name" => ["Bill", "Bob"]}
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#
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# If an attribute is modified in-place then make use of
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# <tt>[attribute_name]_will_change!</tt> to mark that the attribute is changing.
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# Otherwise \Active \Model can't track changes to in-place attributes. Note
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# that Active Record can detect in-place modifications automatically. You do
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# not need to call <tt>[attribute_name]_will_change!</tt> on Active Record models.
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#
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# person.name_will_change!
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# person.name_change # => ["Bill", "Bill"]
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# person.name << 'y'
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# person.name_change # => ["Bill", "Billy"]
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```
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