Undefined method `map' for 1:Fixnum - sql

Question

I want to email users every time a new treatment that is under the category they are interested in is added.
I have a join table interests_users which is holds a user_id and a interest_id. Treatments has a variable called category which is used to compare against interests.
This is what the create block in my treatments controller looks like.
def create
#treatment = Treatment.new(treatment_params)
respond_to do |format|
if #treatment.save
interest = Interest.find_by(name: #treatment.category)
if interest
User.find_by_sql("SELECT * FROM users
INNER JOIN interests_users ON clients.id = interests_users.client_id
WHERE interests_users.interest_id = ?", interest.id).each do |user|
Bestevermailer.treatmentNotification(user, #treatment).deliver
end
end
format.html { redirect_to #treatment, notice: 'Treatment was successfully created.' }
format.json { render :show, status: :created, location: #treatment }
else
format.html { render :new }
format.json { render json: #treatment.errors, status: :unprocessable_entity }
end
end
end
Full Trace
activerecord (4.2.5) lib/active_record/connection_adapters/sqlite3_adapter.rb:289:in `exec_query'
activerecord (4.2.5) lib/active_record/connection_adapters/abstract/database_statements.rb:355:in `select'
activerecord (4.2.5) lib/active_record/connection_adapters/abstract/database_statements.rb:32:in `select_all'
activerecord (4.2.5) lib/active_record/connection_adapters/abstract/query_cache.rb:68:in `block in select_all'
activerecord (4.2.5) lib/active_record/connection_adapters/abstract/query_cache.rb:83:in `cache_sql'
activerecord (4.2.5) lib/active_record/connection_adapters/abstract/query_cache.rb:68:in `select_all'
activerecord (4.2.5) lib/active_record/querying.rb:39:in `find_by_sql'
app/controllers/treatments_controller.rb:72:in `block in create'
actionpack (4.2.5) lib/action_controller/metal/mime_responds.rb:212:in `respond_to'
app/controllers/treatments_controller.rb:68:in `create'
actionpack (4.2.5) lib/action_controller/metal/implicit_render.rb:4:in `send_action'
actionpack (4.2.5) lib/abstract_controller/base.rb:198:in `process_action'
actionpack (4.2.5) lib/action_controller/metal/rendering.rb:10:in `process_action'
actionpack (4.2.5) lib/abstract_controller/callbacks.rb:20:in `block in process_action'
activesupport (4.2.5) lib/active_support/callbacks.rb:117:in `call'
activesupport (4.2.5) lib/active_support/callbacks.rb:117:in `call'
activesupport (4.2.5) lib/active_support/callbacks.rb:555:in `block (2 levels) in compile'
activesupport (4.2.5) lib/active_support/callbacks.rb:505:in `call'
activesupport (4.2.5) lib/active_support/callbacks.rb:505:in `call'
activesupport (4.2.5) lib/active_support/callbacks.rb:92:in `__run_callbacks__'
activesupport (4.2.5) lib/active_support/callbacks.rb:778:in `_run_process_action_callbacks'
activesupport (4.2.5) lib/active_support/callbacks.rb:81:in `run_callbacks'
actionpack (4.2.5) lib/abstract_controller/callbacks.rb:19:in `process_action'
actionpack (4.2.5) lib/action_controller/metal/rescue.rb:29:in `process_action'
actionpack (4.2.5) lib/action_controller/metal/instrumentation.rb:32:in `block in process_action'
activesupport (4.2.5) lib/active_support/notifications.rb:164:in `block in instrument'
activesupport (4.2.5) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
activesupport (4.2.5) lib/active_support/notifications.rb:164:in `instrument'
actionpack (4.2.5) lib/action_controller/metal/instrumentation.rb:30:in `process_action'
actionpack (4.2.5) lib/action_controller/metal/params_wrapper.rb:250:in `process_action'
activerecord (4.2.5) lib/active_record/railties/controller_runtime.rb:18:in `process_action'
actionpack (4.2.5) lib/abstract_controller/base.rb:137:in `process'
actionview (4.2.5) lib/action_view/rendering.rb:30:in `process'
actionpack (4.2.5) lib/action_controller/metal.rb:196:in `dispatch'
actionpack (4.2.5) lib/action_controller/metal/rack_delegation.rb:13:in `dispatch'
actionpack (4.2.5) lib/action_controller/metal.rb:237:in `block in action'
actionpack (4.2.5) lib/action_dispatch/routing/route_set.rb:76:in `call'
actionpack (4.2.5) lib/action_dispatch/routing/route_set.rb:76:in `dispatch'
actionpack (4.2.5) lib/action_dispatch/routing/route_set.rb:45:in `serve'
actionpack (4.2.5) lib/action_dispatch/journey/router.rb:43:in `block in serve'
actionpack (4.2.5) lib/action_dispatch/journey/router.rb:30:in `each'
actionpack (4.2.5) lib/action_dispatch/journey/router.rb:30:in `serve'
actionpack (4.2.5) lib/action_dispatch/routing/route_set.rb:817:in `call'
rack (1.6.4) lib/rack/etag.rb:24:in `call'
rack (1.6.4) lib/rack/conditionalget.rb:38:in `call'
rack (1.6.4) lib/rack/head.rb:13:in `call'
actionpack (4.2.5) lib/action_dispatch/middleware/params_parser.rb:27:in `call'
actionpack (4.2.5) lib/action_dispatch/middleware/flash.rb:260:in `call'
rack (1.6.4) lib/rack/session/abstract/id.rb:225:in `context'
rack (1.6.4) lib/rack/session/abstract/id.rb:220:in `call'
actionpack (4.2.5) lib/action_dispatch/middleware/cookies.rb:560:in `call'
activerecord (4.2.5) lib/active_record/query_cache.rb:36:in `call'
activerecord (4.2.5) lib/active_record/connection_adapters/abstract/connection_pool.rb:653:in `call'
activerecord (4.2.5) lib/active_record/migration.rb:377:in `call'
actionpack (4.2.5) lib/action_dispatch/middleware/callbacks.rb:29:in `block in call'
activesupport (4.2.5) lib/active_support/callbacks.rb:88:in `__run_callbacks__'
activesupport (4.2.5) lib/active_support/callbacks.rb:778:in `_run_call_callbacks'
activesupport (4.2.5) lib/active_support/callbacks.rb:81:in `run_callbacks'
actionpack (4.2.5) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
actionpack (4.2.5) lib/action_dispatch/middleware/reloader.rb:73:in `call'
actionpack (4.2.5) lib/action_dispatch/middleware/remote_ip.rb:78:in `call'
actionpack (4.2.5) lib/action_dispatch/middleware/debug_exceptions.rb:17:in `call'
web-console (2.2.1) lib/web_console/middleware.rb:39:in `call'
actionpack (4.2.5) lib/action_dispatch/middleware/show_exceptions.rb:30:in `call'
railties (4.2.5) lib/rails/rack/logger.rb:38:in `call_app'
railties (4.2.5) lib/rails/rack/logger.rb:20:in `block in call'
activesupport (4.2.5) lib/active_support/tagged_logging.rb:68:in `block in tagged'
activesupport (4.2.5) lib/active_support/tagged_logging.rb:26:in `tagged'
activesupport (4.2.5) lib/active_support/tagged_logging.rb:68:in `tagged'
railties (4.2.5) lib/rails/rack/logger.rb:20:in `call'
actionpack (4.2.5) lib/action_dispatch/middleware/request_id.rb:21:in `call'
rack (1.6.4) lib/rack/methodoverride.rb:22:in `call'
rack (1.6.4) lib/rack/runtime.rb:18:in `call'
activesupport (4.2.5) lib/active_support/cache/strategy/local_cache_middleware.rb:28:in `call'
rack (1.6.4) lib/rack/lock.rb:17:in `call'
actionpack (4.2.5) lib/action_dispatch/middleware/static.rb:116:in `call'
rack (1.6.4) lib/rack/sendfile.rb:113:in `call'
railties (4.2.5) lib/rails/engine.rb:518:in `call'
railties (4.2.5) lib/rails/application.rb:165:in `call'
rack (1.6.4) lib/rack/lock.rb:17:in `call'
rack (1.6.4) lib/rack/content_length.rb:15:in `call'
rack (1.6.4) lib/rack/handler/webrick.rb:88:in `service'
C:/RailsInstaller/Ruby2.1.0/lib/ruby/2.1.0/webrick/httpserver.rb:138:in `service'
C:/RailsInstaller/Ruby2.1.0/lib/ruby/2.1.0/webrick/httpserver.rb:94:in `run'
C:/RailsInstaller/Ruby2.1.0/lib/ruby/2.1.0/webrick/server.rb:295:in `block in start_thread'

Answer 1

Try re-framing your query. Here:
User.joins('INNER JOIN interests_users ON clients.id = interests_users.client_id').where("interests_users.interest_id = ?", interest.id)
As per a similar SO:
find_by_sql doesn't work well with query placeholders

Answer 2

find_by_sql expects an array as a parameter:
User.find_by_sql([
"SELECT * FROM users
INNER JOIN interests_users
ON clients.id = interests_users.client_id
WHERE interests_users.interest_id = ?",
interest.id]).each do |user|