Print out a meaningful error when ActiveRecord::ReadOnlyRecord is raised

Currently, there is no messages which get printed out. Convoluted system
may have hooks that create other objects in which case we only fail with
no messages. This commit changes this information allowing you to know
which object is the one that actually raised the error.

2 files changed, 8 insertions, 5 deletions

diff --git a/activerecord/lib/active_record/persistence.rb b/activerecord/lib/active_record/persistence.rb
index 9d2c9d3b9c..06c8bceb30 100644
--- a/activerecord/lib/active_record/persistence.rb
+++ b/activerecord/lib/active_record/persistence.rb
@@ -188,7 +188,7 @@ module ActiveRecord
     # and <tt>destroy</tt> returns +false+. See
     # ActiveRecord::Callbacks for further details.
     def destroy
-      raise ReadOnlyRecord if readonly?
+      raise ReadOnlyRecord, "#{self.class} is marked as readonly" if readonly?
       destroy_associations
       destroy_row if persisted?
       @destroyed = true
@@ -519,7 +519,7 @@ module ActiveRecord
     end
 
     def create_or_update
-      raise ReadOnlyRecord if readonly?
+      raise ReadOnlyRecord, "#{self.class} is marked as readonly" if readonly?
       result = new_record? ? _create_record : _update_record
       result != false
     end
diff --git a/activerecord/test/cases/readonly_test.rb b/activerecord/test/cases/readonly_test.rb
index 2afd25c989..37d277eaa1 100644
--- a/activerecord/test/cases/readonly_test.rb
+++ b/activerecord/test/cases/readonly_test.rb
@@ -22,9 +22,12 @@ class ReadOnlyTest < ActiveRecord::TestCase
       assert !dev.save
       dev.name = 'Forbidden.'
     end
-    assert_raise(ActiveRecord::ReadOnlyRecord) { dev.save  }
-    assert_raise(ActiveRecord::ReadOnlyRecord) { dev.save! }
-    assert_raise(ActiveRecord::ReadOnlyRecord) { dev.destroy }
+    e = assert_raise(ActiveRecord::ReadOnlyRecord) { dev.save  }
+    assert_equal "Developer is marked as readonly", e.message
+    e = assert_raise(ActiveRecord::ReadOnlyRecord) { dev.save! }
+    assert_equal "Developer is marked as readonly", e.message
+    e = assert_raise(ActiveRecord::ReadOnlyRecord) { dev.destroy }
+    assert_equal "Developer is marked as readonly", e.message
   end