Hanami logger is compatible with the stdlib Logger but it supports structured logging by default. This means that you are encouraged to log data, which we refer to as payloads rather than plain text messages. This approach makes it much easier to process and understand your logs when running your system on production.

In non-production environments, structured logs are turned into easy read text log entries, but the underlying log entries are represented as struct-like objects, even if you pass a text message to your logger.

Basic usage

To log a text entry, simply use a logger method with a name corresponding to the log level that you want to use. Let’s say you want to log an entry with INFO level:

  1. bookshelf[development]> app["logger"].info "Hello World"
  2. # [bookshelf] [INFO] [2022-11-20 13:47:13 +0100] Hello World

If you wanted to log an error:

  1. bookshelf[development]> app["logger"].info "Something's wrong"
  2. # [bookshelf] [ERROR] [2022-11-20 13:48:05 +0100] Something's wrong

The following logging methods are available:

  • debug
  • info
  • warn
  • error
  • fatal

Logging data

In addition to plain text logging, you can log arbitrary data by passing a log entry payload to a log method:

  1. bookshelf[development]> app["logger"].info "Hello World", component: "admin"
  2. # [bookshelf] [INFO] [2022-11-20 13:50:43 +0100] Hello World component="admin"

The text message argument is not mandatory, which means that you can only provide the payload:

  1. bookshelf[development]> app["logger"].info text: "Hello World", component: "admin"
  2. # [bookshelf] [INFO] [2022-11-20 13:51:40 +0100] text="Hello World" component="admin"

Notice that the default development log formatting turns our payload into a key=value representation. It’s easy to read or even parse programatically, but please remember that in any environment where logs are parsed and post-processing using JSON format is the recommended way, and this is how Hanami configures its logger in production environment by default.

Logging exceptions

Hanami logger supports logging exceptions out of the box without the need to write custom formatters. Simply rescue from an exception and pass it to the error log method:

  1. bookshelf[development]> begin
  2. bookshelf[development]>   raise "OH NOEZ!"
  3. bookshelf[development]> rescue => e
  4. bookshelf[development]>   app["logger"].error(e)
  5. bookshelf[development]> end
  6. # [bookshelf] [ERROR] [2022-11-20 13:54:55 +0100]
  7. #   OH NOEZ! (RuntimeError)
  8. #   (pry):7:in `__pry__'
  9. #   ...

You can also pass in any additional information that should be helpful in a payload:

  1. bookshelf[development]> begin
  2. bookshelf[development]>   raise "OH NOEZ!"
  3. bookshelf[development]> rescue => e
  4. bookshelf[development]>   app["logger"].error(e, component: "admin")
  5. bookshelf[development]> end
  6. # [bookshelf] [ERROR] [2022-11-20 13:56:36 +0100] component="console"
  7. #   OH NOEZ! (RuntimeError)
  8. #   (pry):12:in `__pry__'