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Diffstat (limited to 'guides/source/active_record_callbacks.md')
| -rw-r--r-- | guides/source/active_record_callbacks.md | 134 |
1 files changed, 93 insertions, 41 deletions
diff --git a/guides/source/active_record_callbacks.md b/guides/source/active_record_callbacks.md index 971c1cdb25..9c7e60cbb0 100644 --- a/guides/source/active_record_callbacks.md +++ b/guides/source/active_record_callbacks.md @@ -15,7 +15,7 @@ After reading this guide, you will know: The Object Life Cycle --------------------- -During the normal operation of a Rails application, objects may be created, updated, and destroyed. Active Record provides hooks into this <em>object life cycle</em> so that you can control your application and its data. +During the normal operation of a Rails application, objects may be created, updated, and destroyed. Active Record provides hooks into this *object life cycle* so that you can control your application and its data. Callbacks allow you to trigger logic before or after an alteration of an object's state. @@ -35,11 +35,11 @@ class User < ActiveRecord::Base before_validation :ensure_login_has_a_value protected - def ensure_login_has_a_value - if login.nil? - self.login = email unless email.blank? + def ensure_login_has_a_value + if login.nil? + self.login = email unless email.blank? + end end - end end ``` @@ -49,13 +49,13 @@ The macro-style class methods can also receive a block. Consider using this styl class User < ActiveRecord::Base validates :login, :email, presence: true - before_create do |user| - user.name = user.login.capitalize if user.name.blank? + before_create do + self.name = login.capitalize if name.blank? end end ``` -Callbacks can also be registered to only fire on certain lifecycle events: +Callbacks can also be registered to only fire on certain life cycle events: ```ruby class User < ActiveRecord::Base @@ -65,13 +65,13 @@ class User < ActiveRecord::Base after_validation :set_location, on: [ :create, :update ] protected - def normalize_name - self.name = self.name.downcase.titleize - end + def normalize_name + self.name = self.name.downcase.titleize + end - def set_location - self.location = LocationService.query(self) - end + def set_location + self.location = LocationService.query(self) + end end ``` @@ -92,6 +92,7 @@ Here is a list with all the available Active Record callbacks, listed in the sam * `around_create` * `after_create` * `after_save` +* `after_commit/after_rollback` ### Updating an Object @@ -103,12 +104,14 @@ Here is a list with all the available Active Record callbacks, listed in the sam * `around_update` * `after_update` * `after_save` +* `after_commit/after_rollback` ### Destroying an Object * `before_destroy` * `around_destroy` * `after_destroy` +* `after_commit/after_rollback` WARNING. `after_save` runs both on create and update, but always _after_ the more specific callbacks `after_create` and `after_update`, no matter the order in which the macro calls were executed. @@ -141,6 +144,55 @@ You have initialized an object! => #<User id: 1> ``` +### `after_touch` + +The `after_touch` callback will be called whenever an Active Record object is touched. + +```ruby +class User < ActiveRecord::Base + after_touch do |user| + puts "You have touched an object" + end +end + +>> u = User.create(name: 'Kuldeep') +=> #<User id: 1, name: "Kuldeep", created_at: "2013-11-25 12:17:49", updated_at: "2013-11-25 12:17:49"> + +>> u.touch +You have touched an object +=> true +``` + +It can be used along with `belongs_to`: + +```ruby +class Employee < ActiveRecord::Base + belongs_to :company, touch: true + after_touch do + puts 'An Employee was touched' + end +end + +class Company < ActiveRecord::Base + has_many :employees + after_touch :log_when_employees_or_company_touched + + private + def log_when_employees_or_company_touched + puts 'Employee/Company was touched' + end +end + +>> @employee = Employee.last +=> #<Employee id: 1, company_id: 1, created_at: "2013-11-25 17:04:22", updated_at: "2013-11-25 17:05:05"> + +# triggers @employee.company.touch +>> @employee.touch +Employee/Company was touched +An Employee was touched +=> true +``` + Running Callbacks ----------------- @@ -150,16 +202,16 @@ The following methods trigger callbacks: * `create!` * `decrement!` * `destroy` +* `destroy!` * `destroy_all` * `increment!` * `save` * `save!` * `save(validate: false)` * `toggle!` -* `update` * `update_attribute` -* `update_attributes` -* `update_attributes!` +* `update` +* `update!` * `valid?` Additionally, the `after_find` callback is triggered by the following finder methods: @@ -167,7 +219,7 @@ Additionally, the `after_find` callback is triggered by the following finder met * `all` * `first` * `find` -* `find_all_by_*` +* `find_by` * `find_by_*` * `find_by_*!` * `find_by_sql` @@ -175,12 +227,12 @@ Additionally, the `after_find` callback is triggered by the following finder met The `after_initialize` callback is triggered every time a new object of the class is initialized. -NOTE: The `find_all_by_*`, `find_by_*` and `find_by_*!` methods are dynamic finders generated automatically for every attribute. Learn more about them at the [Dynamic finders section](active_record_querying.html#dynamic-finders) +NOTE: The `find_by_*` and `find_by_*!` methods are dynamic finders generated automatically for every attribute. Learn more about them at the [Dynamic finders section](active_record_querying.html#dynamic-finders) Skipping Callbacks ------------------ -Just as with validations, it is also possible to skip callbacks. These methods should be used with caution, however, because important business rules and application logic may be kept in callbacks. Bypassing them without understanding the potential implications may lead to invalid data. +Just as with validations, it is also possible to skip callbacks by using the following methods: * `decrement` * `decrement_counter` @@ -195,6 +247,8 @@ Just as with validations, it is also possible to skip callbacks. These methods s * `update_all` * `update_counters` +These methods should be used with caution, however, because important business rules and application logic may be kept in callbacks. Bypassing them without understanding the potential implications may lead to invalid data. + Halting Execution ----------------- @@ -202,32 +256,32 @@ As you start registering new callbacks for your models, they will be queued for The whole callback chain is wrapped in a transaction. If any _before_ callback method returns exactly `false` or raises an exception, the execution chain gets halted and a ROLLBACK is issued; _after_ callbacks can only accomplish that by raising an exception. -WARNING. Raising an arbitrary exception may break code that expects `save` and its friends not to fail like that. The `ActiveRecord::Rollback` exception is thought precisely to tell Active Record a rollback is going on. That one is internally captured but not reraised. +WARNING. Any exception that is not `ActiveRecord::Rollback` will be re-raised by Rails after the callback chain is halted. Raising an exception other than `ActiveRecord::Rollback` may break code that does not expect methods like `save` and `update_attributes` (which normally try to return `true` or `false`) to raise an exception. Relational Callbacks -------------------- -Callbacks work through model relationships, and can even be defined by them. Suppose an example where a user has many posts. A user's posts should be destroyed if the user is destroyed. Let's add an `after_destroy` callback to the `User` model by way of its relationship to the `Post` model: +Callbacks work through model relationships, and can even be defined by them. Suppose an example where a user has many articles. A user's articles should be destroyed if the user is destroyed. Let's add an `after_destroy` callback to the `User` model by way of its relationship to the `Article` model: ```ruby class User < ActiveRecord::Base - has_many :posts, dependent: :destroy + has_many :articles, dependent: :destroy end -class Post < ActiveRecord::Base +class Article < ActiveRecord::Base after_destroy :log_destroy_action def log_destroy_action - puts 'Post destroyed' + puts 'Article destroyed' end end >> user = User.first => #<User id: 1> ->> user.posts.create! -=> #<Post id: 1, user_id: 1> +>> user.articles.create! +=> #<Article id: 1, user_id: 1> >> user.destroy -Post destroyed +Article destroyed => #<User id: 1> ``` @@ -274,7 +328,7 @@ When writing conditional callbacks, it is possible to mix both `:if` and `:unles ```ruby class Comment < ActiveRecord::Base after_create :send_email_to_author, if: :author_wants_emails?, - unless: Proc.new { |comment| comment.post.ignore_comments? } + unless: Proc.new { |comment| comment.article.ignore_comments? } end ``` @@ -288,7 +342,7 @@ Here's an example where we create a class with an `after_destroy` callback for a ```ruby class PictureFileCallbacks def after_destroy(picture_file) - if File.exists?(picture_file.filepath) + if File.exist?(picture_file.filepath) File.delete(picture_file.filepath) end end @@ -308,7 +362,7 @@ Note that we needed to instantiate a new `PictureFileCallbacks` object, since we ```ruby class PictureFileCallbacks def self.after_destroy(picture_file) - if File.exists?(picture_file.filepath) + if File.exist?(picture_file.filepath) File.delete(picture_file.filepath) end end @@ -343,19 +397,17 @@ By using the `after_commit` callback we can account for this case. ```ruby class PictureFile < ActiveRecord::Base - attr_accessor :delete_file - - after_destroy do |picture_file| - picture_file.delete_file = picture_file.filepath - end + after_commit :delete_picture_file_from_disk, on: [:destroy] - after_commit do |picture_file| - if picture_file.delete_file && File.exist?(picture_file.delete_file) - File.delete(picture_file.delete_file) - picture_file.delete_file = nil + def delete_picture_file_from_disk + if File.exist?(filepath) + File.delete(filepath) end end end ``` -The `after_commit` and `after_rollback` callbacks are guaranteed to be called for all models created, updated, or destroyed within a transaction block. If any exceptions are raised within one of these callbacks, they will be ignored so that they don't interfere with the other callbacks. As such, if your callback code could raise an exception, you'll need to rescue it and handle it appropriately within the callback. +NOTE: the `:on` option specifies when a callback will be fired. If you +don't supply the `:on` option the callback will fire for every action. + +WARNING. The `after_commit` and `after_rollback` callbacks are guaranteed to be called for all models created, updated, or destroyed within a transaction block. If any exceptions are raised within one of these callbacks, they will be ignored so that they don't interfere with the other callbacks. As such, if your callback code could raise an exception, you'll need to rescue it and handle it appropriately within the callback. |