> > article.errors.full_message(:title, "cannot be blank") > > => "Title cannot be blank" > > ``` The default format can be overridden globally using a language-specific locale file. ```yaml # config/locales/en.yml en: errors: format: "'%{attribute}' %{message}" ``` With this change, the full error message is changed for all the attributes of all models. ```ruby > > article = Article.new > > => #

> > article.errors.full_message(:title, "cannot be blank") > > => "'Title' cannot be blank" > > user = User.new > > => # > > user.errors.full_message(:first_name, "cannot be blank") > > => "'First name' cannot be blank" > > ``` This trick works in some cases but it doesn't work if we have to customize the error messages on the basis of specific models or attributes. Before Rails 6, there is no easy way to generate error messages like shown below. ```plaintext The article's title cannot be empty ``` or ```plaintext First name of a person cannot be blank ``` If we change the `errors.format` to `The article's %{attribute} %{message}` in `config/locales/en.yml` then that format will be unexpectedly used for other models, too. ```yaml # config/locales/en.yml en: errors: format: "The article's %{attribute} %{message}" ``` This is what will happen if we make such a change. ```ruby > > article = Article.new > > => #

> > article.errors.full_message(:title, "cannot be empty") > > => "The article's Title cannot be empty" > > user = User.new > > => # > > user.errors.full_message(:first_name, "cannot be blank") > > => "The article's First name cannot be blank" > > ``` Notice the error message generated for the `:first_name` attribute of User model. This does not look the way we want, right? Let's see what is changed in Rails 6 to overcome this problem. ## Enhancements made to `ActiveModel::Errors#full_message` in Rails 6 Overriding the format of error message globally using `errors.format` is still supported in Rails 6. In addition to that, Rails 6 now also supports overriding the error message's format at the model level and at the attribute level. In order to enable this support, we need to explicitly set `config.active_model.i18n_customize_full_message` to `true` in the Rails configuration file, preferably in `config/application.rb` which is implicitly set to `false` by default. ##### Overriding model level format We can customize the full error message format for each model separately. ```yaml # config/locales/en.yml en: activerecord: errors: models: article: format: "`%{attribute}`: %{message}" user: format: "%{attribute} of the user %{message}" ``` The full error messages will look like this. ```ruby > > article = Article.new > > => #

> > article.errors.full_message(:title, "cannot be empty") > > => "`Title`: cannot be empty" > > article.valid? > > => false > > article.errors.full_messages > > => ["`Title`: can't be blank"] > > user = User.new > > => # > > user.errors.full_message(:first_name, "cannot be blank") > > => "First name of the user cannot be blank" > > comment = Comment.new > > => # > > comment.errors.full_message(:message, "is required") > > => "Message is required" > > ``` Notice how the default format `%{attribute} %{message}` is used for generating the full error messages for the `Comment` model since its format is not being overridden. Since the other methods such as `ActiveModel::Errors#full_messages`, `ActiveModel::Errors#full_messages_for`, `ActiveModel::Errors#to_hash` etc. use the `ActiveModel::Errors#full_message` method under the hood, we get the full error messages according to the custom format in the returned values of these methods respectively as expected. ##### Overriding attribute level format Similar to customizing format at the model level, we can customize the error format for specific attributes of individual models. ```yaml # config/locales/en.yml en: activerecord: errors: models: article: attributes: title: format: "The article's title %{message}" user: attributes: first_name: format: "%{attribute} of a person %{message}" ``` With such a configuration, we get the customized error message for the `title` attribute of the Article model. ```ruby > > article = Article.new > > => #

> > article.errors.full_message(:title, "cannot be empty") > > => "The article's title cannot be empty" > > article.errors.full_message(:description, "cannot be empty") > > => "Description cannot be empty" > > user = User.new > > => # > > user.errors.full_message(:first_name, "cannot be blank") > > => "First name of a person cannot be blank" > > user.errors.full_message(:last_name, "cannot be blank") > > => "Last name cannot be blank" > > ``` Note that the error messages for the rest of the attributes were generated using the default `%{attribute} %{message}` format for which we didn't add custom formats in the `config/locales/en.yml` manifest. ##### Overriding model level format of deeply nested models ```yaml # config/locales/en.yml en: activerecord: errors: models: article/comments/attachments: format: "%{message}" ``` ```ruby > > article = Article.new > > => #

> > article.errors.full_message(:'comments/attachments.file_name', "is required") > > => "is required" > > article.errors.full_message(:'comments/attachments.path', "cannot be blank") > > => "cannot be blank" > > article.errors.full_message(:'comments.message', "cannot be blank") > > => "Comments message cannot be blank" > > ``` ##### Overriding attribute level format of deeply nested models ```yaml # config/locales/en.yml en: activerecord: errors: models: article/comments/attachments: attributes: file_name: format: "File name of an attachment %{message}" ``` ```ruby > > article = Article.new > > => #

> > article.errors.full_message(:'comments/attachments.file_name', "is required") > > => "File name of an attachment is required" > > article.errors.full_message(:'comments/attachments.path', "cannot be blank") > > => "Comments/attachments path cannot be blank" > > ``` ## Precedence The custom formats specified in the locale file has the following precedence in the high to low order. - `activerecord.errors.models.article/comments/attachments.attributes.file_name.format` - `activerecord.errors.models.article/comments/attachments.format` - `activerecord.errors.models.article.attributes.title.format` - `activerecord.errors.models.article.format` - `errors.format` --- To learn more, please checkout [rails/rails#32956](https://github.com/rails/rails/pull/32956) and [rails/rails#35789](https://github.com/rails/rails/pull/35789). ## Links - [Human page](https://www.bigbinary.com/blog/rails-6-allows-to-override-the-activemodel-errors-full_message-format-at-the-model-level-and-at-the-attribute-level)