Improve SimpleJob docs regarding attribute changes (#68)

Co-authored-by: Martijn Vermaat <[email protected]>

README.md

@@ -88,6 +88,10 @@ Note that at this point only arguments that are raw JSON types are supported:
 
 If you need marshalable Ruby types there instead, you might need to implement a custom `Serializer.`
 
+### Sqewer::SimpleJob
+
+The module `Sqewer::SimpleJob` can be included to a job class to add some features, specially dealing with attributes, see more details [here](https://github.com/WeTransfer/sqewer/blob/master/lib/sqewer/simple_job.rb).
+
 ## Jobs spawning dependent jobs
 
 If your `run` method on the job object accepts arguments (has non-zero `arity` ) the `ExecutionContext` will

lib/sqewer/simple_job.rb

@@ -4,6 +4,13 @@
 # * initialize() will have keyword access to all accessors, and will ensure you have called each one of them
 # * to_h() will produce a symbolized Hash with all the properties defined using attr_accessor, and the job_class_name
 # * inspect() will provide a sensible default string representation for logging
+#
+# This module validates if the attributes defined in the job class are the same as
+# those persisted in the queue. More details on `Sqewer::SimpleJob#initialize`.
+# Because of this, it's required to create a new job class when adding or removing
+# an attribute.
+# This mechanism guarantees strong consistency. Without it, a new deployed job class
+# could process old incompatible payloads.
 module Sqewer::SimpleJob
   UnknownJobAttribute = Class.new(Sqewer::Error)
   MissingAttribute = Class.new(Sqewer::Error)
@@ -53,7 +60,7 @@ def initialize(**jobargs)
       accessor = "#{k}="
       touched_attributes << k
       unless respond_to?(accessor)
-        raise UnknownJobAttribute, "Unknown attribute #{k.inspect} for #{self.class}" 
+        raise UnknownJobAttribute, "Unknown attribute #{k.inspect} for #{self.class}"
       end
 
       send("#{k}=", v)