Support :if and :unless options for callbacks which pass-thru to Rails

CHANGELOG.md

@@ -1,6 +1,7 @@
 ### 0.7.1 (Next)
 
 * [#208](https://github.com/mongoid/mongoid-history/pull/208): Fix: history tracks fields declared after `track_history` - [@mikwat](https://github.com/mikwat).
+* [#209](https://github.com/mongoid/mongoid-history/pull/209): `track_history` method support for `:if` and `:unless` options - [@johnnyshields](https://github.com/johnnyshields).
 * Your contribution here.
 
 ### 0.7.0 (2017/11/14)

README.md

@@ -429,6 +429,18 @@ Or perhaps you are namespacing to a module:
 Mongoid::History.modifier_class_name = 'CMS::Author'
 ```
 
+**Conditional :if and :unless options**
+
+The `track_history` method supports `:if` and `:unless` options which will skip generating
+the history tracker unless they are satisfied. These options can take either a method
+`Symbol` or a `Proc`. They behave identical to how `:if` and `:unless` behave in Rails model callbacks.
+
+```ruby
+  track_history on: [:ip],
+                if: :should_i_track_history?,
+                unless: ->(obj){ obj.method_to_skip_history }
+```
+
 **Using an alternate changes method**
 
 Sometimes you may wish to provide an alternate method for determining which changes should be tracked.  For example, if you are using embedded documents

lib/mongoid/history/trackable.rb

@@ -21,9 +21,10 @@ def track_history(options = {})
           delegate :history_trackable_options, to: 'self.class'
           delegate :track_history?, to: 'self.class'
 
-          around_update :track_update if history_options.options[:track_update]
-          around_create :track_create if history_options.options[:track_create]
-          around_destroy :track_destroy if history_options.options[:track_destroy]
+          callback_options = history_options.options.slice(:if, :unless)
+          around_update :track_update, callback_options if history_options.options[:track_update]
+          around_create :track_create, callback_options if history_options.options[:track_create]
+          around_destroy :track_destroy, callback_options if history_options.options[:track_destroy]
 
           Mongoid::History.trackable_class_options ||= {}
           Mongoid::History.trackable_class_options[history_options.scope] = history_options

spec/unit/callback_options_spec.rb

@@ -0,0 +1,59 @@
+require 'spec_helper'
+
+describe Mongoid::History::Options do
+  before :all do
+    ModelOne = Class.new do
+      include Mongoid::Document
+      include Mongoid::History::Trackable
+      store_in collection: :model_ones
+      field :foo
+      attr_accessor :bar
+      track_history track_create: true,
+                    track_update: true,
+                    track_destroy: true,
+                    if: :bar
+    end
+
+    ModelTwo = Class.new do
+      include Mongoid::Document
+      include Mongoid::History::Trackable
+      store_in collection: :model_twos
+      field :foo
+      attr_accessor :bar
+      track_history track_create: true,
+                    track_update: true,
+                    track_destroy: true,
+                    unless: ->(obj){obj.bar}
+    end
+
+    ModelThree = Class.new do
+      include Mongoid::Document
+      include Mongoid::History::Trackable
+      store_in collection: :model_threes
+      field :foo
+      attr_accessor :bar, :baz
+      track_history track_create: true,
+                    track_update: true,
+                    track_destroy: true,
+                    if: ->(obj){obj.bar}, unless: :baz
+    end
+  end
+
+  describe ':if' do
+    # TODO: ModelOne
+  end
+
+  describe ':unless' do
+    # TODO: ModelTwo
+  end
+
+  describe ':if and :unless' do
+    # TODO: ModelThree
+  end
+
+  after :all do
+    Object.send(:remove_const, :ModelOne)
+    Object.send(:remove_const, :ModelTwo)
+    Object.send(:remove_const, :ModelThree)
+  end
+end