Class: ActiveSupport::LogSubscriber

Inherits:
Subscriber show all
Defined in:
lib/active_support/log_subscriber.rb,
lib/active_support/log_subscriber/test_helper.rb

Overview

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
    def sql(event)
      info "#{event.payload[:name]} (#{event.duration}) #{event.payload[:sql]}"
    end
  end
end

And it's finally registered as:

ActiveRecord::LogSubscriber.attach_to :active_record

Since we need to know all instance methods before attaching the log subscriber, the line above should be called after your ActiveRecord::LogSubscriber definition.

A logger also needs to be set with ActiveRecord::LogSubscriber.logger=. This 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

Log subscriber also has some helpers to deal with logging and automatically flushes all logs when the request finishes (via action_dispatch.callback notification) in a Rails environment.

Defined Under Namespace

Modules: TestHelper

Constant Summary collapse

CLEAR =

Embed in a String to clear all previous ANSI sequences.

"\e[0m"
BOLD =
"\e[1m"
BLACK =

Colors

"\e[30m"
RED =
"\e[31m"
GREEN =
"\e[32m"
YELLOW =
"\e[33m"
BLUE =
"\e[34m"
MAGENTA =
"\e[35m"
CYAN =
"\e[36m"
WHITE =
"\e[37m"

Class Attribute Summary collapse

Attributes inherited from Subscriber

#patterns

Class Method Summary collapse

Instance Method Summary collapse

Methods inherited from Subscriber

attach_to, detach_from, #initialize, method_added, subscribers

Constructor Details

This class inherits a constructor from ActiveSupport::Subscriber

Class Attribute Details

.loggerObject


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# File 'lib/active_support/log_subscriber.rb', line 83

def logger
  @logger ||= if defined?(Rails) && Rails.respond_to?(:logger)
    Rails.logger
  end
end

Class Method Details

.flush_all!Object

Flush all log_subscribers' logger.


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# File 'lib/active_support/log_subscriber.rb', line 96

def flush_all!
  logger.flush if logger.respond_to?(:flush)
end

.log_subscribersObject


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# File 'lib/active_support/log_subscriber.rb', line 91

def log_subscribers
  subscribers
end

Instance Method Details

#finish(name, id, payload) ⇒ Object


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# File 'lib/active_support/log_subscriber.rb', line 114

def finish(name, id, payload)
  super if logger
rescue => e
  if logger
    logger.error "Could not log #{name.inspect} event. #{e.class}: #{e.message} #{e.backtrace}"
  end
end

#loggerObject


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# File 'lib/active_support/log_subscriber.rb', line 106

def logger
  LogSubscriber.logger
end

#start(name, id, payload) ⇒ Object


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# File 'lib/active_support/log_subscriber.rb', line 110

def start(name, id, payload)
  super if logger
end