From ae989c4170e2ea769e92a54bb431c80c2be30d36 Mon Sep 17 00:00:00 2001
From: Grey Baker <greysteil@gmail.com>
Date: Tue, 26 Jul 2016 10:45:03 +0100
Subject: [PATCH] Handle custom transition association names gracefully

Previously, statesman required the association with the transition class to use
the exact name of the transition class, unless a `transition_name` was specified
along with the `transition_class`.

This PR updates the way we look for the association with the transition class so
as `transition_name` no longer needs to be overridden to work with custom named
associations.
---
 .../adapters/active_record_queries.rb         |  8 ++++-
 lib/statesman/exceptions.rb                   |  1 +
 .../adapters/active_record_queries_spec.rb    | 32 ++++++++++++++++---
 3 files changed, 36 insertions(+), 5 deletions(-)

diff --git a/lib/statesman/adapters/active_record_queries.rb b/lib/statesman/adapters/active_record_queries.rb
index ce9ee544..3e4e8e42 100644
--- a/lib/statesman/adapters/active_record_queries.rb
+++ b/lib/statesman/adapters/active_record_queries.rb
@@ -38,7 +38,13 @@ def transition_name
         end
 
         def transition_reflection
-          reflect_on_association(transition_name)
+          reflect_on_all_associations(:has_many).each do |value|
+            return value if value.klass == transition_class
+          end
+
+          raise MissingTransitionAssociation,
+                "Could not find has_many association between #{self.class} " \
+                "and #{transition_class}."
         end
 
         def model_foreign_key
diff --git a/lib/statesman/exceptions.rb b/lib/statesman/exceptions.rb
index e490c904..8ec2bf63 100644
--- a/lib/statesman/exceptions.rb
+++ b/lib/statesman/exceptions.rb
@@ -5,6 +5,7 @@ class InvalidCallbackError < StandardError; end
   class GuardFailedError < StandardError; end
   class TransitionFailedError < StandardError; end
   class TransitionConflictError < StandardError; end
+  class MissingTransitionAssociation < StandardError; end
 
   class UnserializedMetadataError < StandardError
     def initialize(transition_class_name)
diff --git a/spec/statesman/adapters/active_record_queries_spec.rb b/spec/statesman/adapters/active_record_queries_spec.rb
index 8968cfb7..660a2a65 100644
--- a/spec/statesman/adapters/active_record_queries_spec.rb
+++ b/spec/statesman/adapters/active_record_queries_spec.rb
@@ -125,14 +125,18 @@ def self.initial_state
     end
   end
 
-  context "with a transition name" do
+  context "with a custom name for the transition association" do
     before do
+      # Switch to using OtherActiveRecordModelTransition, so the existing
+      # relation with MyActiveRecordModelTransition doesn't interfere with
+      # this spec.
       MyActiveRecordModel.send(:has_many,
                                :custom_name,
-                               class_name: 'MyActiveRecordModelTransition')
+                               class_name: 'OtherActiveRecordModelTransition')
+
       MyActiveRecordModel.class_eval do
-        def self.transition_name
-          :custom_name
+        def self.transition_class
+          OtherActiveRecordModelTransition
         end
       end
     end
@@ -142,4 +146,24 @@ def self.transition_name
       specify { expect { query }.to_not raise_error }
     end
   end
+
+  context "with no association with the transition class" do
+    before do
+      class UnknownModelTransition < OtherActiveRecordModelTransition; end
+
+      MyActiveRecordModel.class_eval do
+        def self.transition_class
+          UnknownModelTransition
+        end
+      end
+    end
+
+    describe ".in_state" do
+      subject(:query) { MyActiveRecordModel.in_state(:succeeded) }
+
+      it "raises a helpful error" do
+        expect { query }.to raise_error(Statesman::MissingTransitionAssociation)
+      end
+    end
+  end
 end