Active Support Log Subscriber¶ ↑
ActiveSupport::LogSubscriber is an object set to consume ActiveSupport::Notifications with the sole purpose of logging them. The log subscriber dispatches notifications to a registered object based on its given namespace.
An example would be Active Record log subscriber responsible for logging queries:
module ActiveRecord class LogSubscriber < ActiveSupport::LogSubscriber attach_to :active_record def sql(event) info "#{event.payload[:name]} (#{event.duration}) #{event.payload[:sql]}" end end end
ActiveRecord::LogSubscriber.logger must be set as well, but it is assigned automatically in a Rails environment.
After configured, whenever a "sql.active_record" notification is published, it will properly dispatch the event (ActiveSupport::Notifications::Event) to the sql method.
Being an ActiveSupport::Notifications consumer, ActiveSupport::LogSubscriber exposes a simple interface to check if instrumented code raises an exception. It is common to log a different message in case of an error, and this can be achieved by extending the previous example:
module ActiveRecord class LogSubscriber < ActiveSupport::LogSubscriber def sql(event) exception = event.payload[:exception] if exception exception_object = event.payload[:exception_object] error "[ERROR] #{event.payload[:name]}: #{exception.join(', ')} " \ "(#{exception_object.backtrace.first})" else # standard logger code end end end end
ActiveSupport::LogSubscriber also has some helpers to deal with logging. For example, ActiveSupport::LogSubscriber.flush_all! will ensure that all logs are flushed, and it is called in Rails::Rack::Logger after a request finishes.
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Constants
| LEVEL_CHECKS | = | { debug: -> (logger) { !logger.debug? }, info: -> (logger) { !logger.info? }, error: -> (logger) { !logger.error? }, } |
Attributes
| [W] | logger |
Class Public methods
flush_all!() Link
Flush all log_subscribers‘ logger.