"NoMethodError in TasksController#update" -- why? - ruby-on-rails

Question

I'm learning Rails (so this is probably a stupid error). I'm trying to write an edit screen that updates a parent and its children at the same time. When I hit save I get:
NoMethodError in TasksController#update
undefined method `to_sym' for #<Arel::Attributes::Integer:0x00000004d11970>
I can't figure out what has caused this and where/what this integer object is. Can anyone give me any pointers?
EDIT: I can make this work if I start from scratch with a new Rails project. The parameters that are raising the error are the ones under the key "flactions_attributes". There seem to be some values missing from that, but that's not the problem.
Detail
The parent model is Task, the child is Flaction. (Take it from me, you don't want to name a table 'action' in Rails...)
The Error page also helpfully shows the params hash (please pardon my 'comedy' test data.):
{"utf8"=>"✓",
"_method"=>"put",
"authenticity_token"=>"QS1gVSz+LKNIyBsIdnSMVfciBA+3j0nFK37477A7mps=",
"task"=>{"name"=>"Finish secret lair",
"description"=>"",
"flactions_attributes"=>{"0"=>{"name"=>"Choose a colour scheme",
"notes"=>"Ask The Voices?",
"id"=>"80"},
"1"=>{"name"=>"Pick a name",
"notes"=>"Something with skulls in it?",
"id"=>"81"}}},
"x"=>"3",
"y"=>"14",
"id"=>"53"}
Here's the update method in the controller. AFAICS it's completely vanilla:
def update
#task = Task.find(params[:id])
respond_to do |format|
if #task.update_attributes(params[:task])
format.html { redirect_to(#task, :notice => 'Task was successfully updated.') }
format.xml { head :ok }
else
format.html { render :action => "edit" }
format.xml { render :xml => #task.errors, :status => :unprocessable_entity }
end
end
end
So: #task.update_attributes finds an integer and tries to run to_sym on it. The only thing I pass to update_attributes is params, and there are no integer keys there. How do I work out what is going on?
Here's the _form file, FWIW:
<%= form_for(#task) do |f| %>
<% if #task.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(#task.errors.count, "error") %> prohibited this task from being saved:</h2>
<ul>
<% #task.errors.full_messages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
</div>
<% end %>
<div class="<%= #task.hold ? 'task held' : 'task' %>" >
<div class="field name">
<%= f.text_field :name, size: 20 %>
<span class="buttons">
<%= if #task.hold
link_to image_tag('unhold-icon.png', alt: 'Un-hold'), change_hold_task_path(#task)
else
link_to image_tag('hold-icon.png', alt: 'Hold'), change_hold_task_path(#task)
end %>
<%= link_to image_tag('delete-icon.png', alt: 'Delete'), #task, confirm: 'Are you sure?', method: :delete %>
</span>
</div>
<div class="field desc">
<%= f.text_area :description, rows: 3, cols: 95 %>
</div>
<table>
<% f.fields_for :flactions do |a| %>
<tr>
<td class="field"> <%= a.text_field :name %> </td>
<td class="field"> <%= a.text_area :notes, rows: 2, columns: 40 %> </td>
<td class="buttons">
<%= link_to image_tag("up-icon-small.png", alt: 'Move Up'), move_flaction_path(a.object, direction: "up") %>
<%= link_to image_tag("down-icon-small.png", alt: 'Move Down'), move_flaction_path(a.object, direction: "down") %>
<%= link_to image_tag("delete-icon-small.png", alt: 'Delete'), a.object, :confirm => 'Are you sure?', :method => :delete %>
</td>
</tr>
<% end # f.fields_for %>
</table>
<%= image_submit_tag('save-icon.png', alt: 'Save') %>
</div> <!-- of div.task or div.task_held -->
<% end %>
EDIT: Stack trace, as requested:
activerecord (3.0.8) lib/active_record/base.rb:1267:in `block in expand_hash_conditions_for_aggregates'
activerecord (3.0.8) lib/active_record/base.rb:1266:in `each'
activerecord (3.0.8) lib/active_record/base.rb:1266:in `expand_hash_conditions_for_aggregates'
activerecord (3.0.8) lib/active_record/relation/query_methods.rb:225:in `build_where'
activerecord (3.0.8) lib/active_record/relation/query_methods.rb:76:in `where'
activerecord (3.0.8) lib/active_record/relation/spawn_methods.rb:124:in `apply_finder_options'
activerecord (3.0.8) lib/active_record/relation/finder_methods.rb:143:in `all'
activerecord (3.0.8) lib/active_record/nested_attributes.rb:364:in `assign_nested_attributes_for_collection_association'
activerecord (3.0.8) lib/active_record/nested_attributes.rb:254:in `flactions_attributes='
activerecord (3.0.8) lib/active_record/base.rb:1564:in `block in attributes='
activerecord (3.0.8) lib/active_record/base.rb:1560:in `each'
activerecord (3.0.8) lib/active_record/base.rb:1560:in `attributes='
activerecord (3.0.8) lib/active_record/persistence.rb:131:in `block in update_attributes'
activerecord (3.0.8) lib/active_record/transactions.rb:292:in `block in with_transaction_returning_status'
activerecord (3.0.8) lib/active_record/connection_adapters/abstract/database_statements.rb:139:in `transaction'
activerecord (3.0.8) lib/active_record/transactions.rb:207:in `transaction'
activerecord (3.0.8) lib/active_record/transactions.rb:290:in `with_transaction_returning_status'
activerecord (3.0.8) lib/active_record/persistence.rb:130:in `update_attributes'
app/controllers/tasks_controller.rb:62:in `block in update'
actionpack (3.0.8) lib/action_controller/metal/mime_responds.rb:264:in `call'
actionpack (3.0.8) lib/action_controller/metal/mime_responds.rb:264:in `retrieve_response_from_mimes'
actionpack (3.0.8) lib/action_controller/metal/mime_responds.rb:191:in `respond_to'
app/controllers/tasks_controller.rb:61:in `update'
actionpack (3.0.8) lib/action_controller/metal/implicit_render.rb:4:in `send_action'
actionpack (3.0.8) lib/abstract_controller/base.rb:150:in `process_action'
actionpack (3.0.8) lib/action_controller/metal/rendering.rb:11:in `process_action'
actionpack (3.0.8) lib/abstract_controller/callbacks.rb:18:in `block in process_action'
activesupport (3.0.8) lib/active_support/callbacks.rb:436:in `_run__950750868564864989__process_action__1833593346352443574__callbacks'
activesupport (3.0.8) lib/active_support/callbacks.rb:410:in `_run_process_action_callbacks'
activesupport (3.0.8) lib/active_support/callbacks.rb:94:in `run_callbacks'
actionpack (3.0.8) lib/abstract_controller/callbacks.rb:17:in `process_action'
actionpack (3.0.8) lib/action_controller/metal/instrumentation.rb:30:in `block in process_action'
activesupport (3.0.8) lib/active_support/notifications.rb:52:in `block in instrument'
activesupport (3.0.8) lib/active_support/notifications/instrumenter.rb:21:in `instrument'
activesupport (3.0.8) lib/active_support/notifications.rb:52:in `instrument'
actionpack (3.0.8) lib/action_controller/metal/instrumentation.rb:29:in `process_action'
actionpack (3.0.8) lib/action_controller/metal/rescue.rb:17:in `process_action'
actionpack (3.0.8) lib/abstract_controller/base.rb:119:in `process'
actionpack (3.0.8) lib/abstract_controller/rendering.rb:41:in `process'
actionpack (3.0.8) lib/action_controller/metal.rb:138:in `dispatch'
actionpack (3.0.8) lib/action_controller/metal/rack_delegation.rb:14:in `dispatch'
actionpack (3.0.8) lib/action_controller/metal.rb:178:in `block in action'
actionpack (3.0.8) lib/action_dispatch/routing/route_set.rb:62:in `call'
actionpack (3.0.8) lib/action_dispatch/routing/route_set.rb:62:in `dispatch'
actionpack (3.0.8) lib/action_dispatch/routing/route_set.rb:27:in `call'
rack-mount (0.6.14) lib/rack/mount/route_set.rb:148:in `block in call'
rack-mount (0.6.14) lib/rack/mount/code_generation.rb:93:in `block in recognize'
rack-mount (0.6.14) lib/rack/mount/code_generation.rb:68:in `optimized_each'
rack-mount (0.6.14) lib/rack/mount/code_generation.rb:92:in `recognize'
rack-mount (0.6.14) lib/rack/mount/route_set.rb:139:in `call'
actionpack (3.0.8) lib/action_dispatch/routing/route_set.rb:493:in `call'
actionpack (3.0.8) lib/action_dispatch/middleware/best_standards_support.rb:17:in `call'
actionpack (3.0.8) lib/action_dispatch/middleware/head.rb:14:in `call'
rack (1.2.3) lib/rack/methodoverride.rb:24:in `call'
actionpack (3.0.8) lib/action_dispatch/middleware/params_parser.rb:21:in `call'
actionpack (3.0.8) lib/action_dispatch/middleware/flash.rb:182:in `call'
actionpack (3.0.8) lib/action_dispatch/middleware/session/abstract_store.rb:149:in `call'
actionpack (3.0.8) lib/action_dispatch/middleware/cookies.rb:302:in `call'
activerecord (3.0.8) lib/active_record/query_cache.rb:32:in `block in call'
activerecord (3.0.8) lib/active_record/connection_adapters/abstract/query_cache.rb:28:in `cache'
activerecord (3.0.8) lib/active_record/query_cache.rb:12:in `cache'
activerecord (3.0.8) lib/active_record/query_cache.rb:31:in `call'
activerecord (3.0.8) lib/active_record/connection_adapters/abstract/connection_pool.rb:354:in `call'
actionpack (3.0.8) lib/action_dispatch/middleware/callbacks.rb:46:in `block in call'
activesupport (3.0.8) lib/active_support/callbacks.rb:416:in `_run_call_callbacks'
actionpack (3.0.8) lib/action_dispatch/middleware/callbacks.rb:44:in `call'
rack (1.2.3) lib/rack/sendfile.rb:107:in `call'
actionpack (3.0.8) lib/action_dispatch/middleware/remote_ip.rb:48:in `call'
actionpack (3.0.8) lib/action_dispatch/middleware/show_exceptions.rb:47:in `call'
railties (3.0.8) lib/rails/rack/logger.rb:13:in `call'
rack (1.2.3) lib/rack/runtime.rb:17:in `call'
activesupport (3.0.8) lib/active_support/cache/strategy/local_cache.rb:72:in `call'
rack (1.2.3) lib/rack/lock.rb:11:in `block in call'
<internal:prelude>:10:in `synchronize'
rack (1.2.3) lib/rack/lock.rb:11:in `call'
actionpack (3.0.8) lib/action_dispatch/middleware/static.rb:30:in `call'
railties (3.0.8) lib/rails/application.rb:168:in `call'
railties (3.0.8) lib/rails/application.rb:77:in `method_missing'
railties (3.0.8) lib/rails/rack/log_tailer.rb:14:in `call'
rack (1.2.3) lib/rack/content_length.rb:13:in `call'
rack (1.2.3) lib/rack/handler/webrick.rb:52:in `service'
/usr/lib/ruby/1.9.2-p180/webrick/httpserver.rb:111:in `service'
/usr/lib/ruby/1.9.2-p180/webrick/httpserver.rb:70:in `run'
/usr/lib/ruby/1.9.2-p180/webrick/server.rb:183:in `block in start_thread'

Answer 1

GOT IT! This wins my personal running prize for the least helpful Rails error ... so far.
The problem was caused because I'd written my own Task.flactions method in the model. Once I deleted that, it worked fine. So, one more thing to remember never to do again: don't override methods that Rails creates for you.
Incidentally, as far as I can tell, the ONLY place parent-child forms in Rails 3 are currently documented is in ri form_for. There are examples there, too. Worth looking at.