rails sum multiple fields - sql

Question

I'm trying to do this supposingly simple operation in rails:
self.timesheets.select("sum(total) as total, sum(quantity) as quantity").first where self is a project
When I do it in console mode, it works but it renders me 3 columns:
[#<Timesheet id: nil, quantity: 120.1, total: 6245.2>]
When I run it in the app, I get this error message:
PG::GroupingError - ERROR: column "timesheets.id" must appear in the GROUP BY clause or be used in an aggregate function
LINE 1: ..." WHERE "timesheets"."project_id" = $1 ORDER BY "timesheet...
^
:
activerecord (4.0.0) lib/active_record/connection_adapters/postgresql_adapter.rb:811:in `prepare_statement'
activerecord (4.0.0) lib/active_record/connection_adapters/postgresql_adapter.rb:772:in `exec_cache'
schema_plus (1.3.1) lib/schema_plus/active_record/connection_adapters/postgresql_adapter.rb:231:in `exec_cache_with_schema_plus'
activerecord (4.0.0) lib/active_record/connection_adapters/postgresql/database_statements.rb:139:in `block in exec_query'
activerecord (4.0.0) lib/active_record/connection_adapters/abstract_adapter.rb:425:in `block in log'
activesupport (4.0.0) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
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activerecord (4.0.0) lib/active_record/connection_adapters/postgresql/database_statements.rb:137:in `exec_query'
activerecord (4.0.0) lib/active_record/connection_adapters/postgresql_adapter.rb:885:in `select'
activerecord (4.0.0) lib/active_record/connection_adapters/abstract/database_statements.rb:24:in `select_all'
activerecord (4.0.0) lib/active_record/connection_adapters/abstract/query_cache.rb:61:in `block in select_all'
activerecord (4.0.0) lib/active_record/connection_adapters/abstract/query_cache.rb:76:in `cache_sql'
activerecord (4.0.0) lib/active_record/connection_adapters/abstract/query_cache.rb:61:in `select_all'
activerecord (4.0.0) lib/active_record/querying.rb:36:in `find_by_sql'
activerecord (4.0.0) lib/active_record/relation.rb:585:in `exec_queries'
activerecord (4.0.0) lib/active_record/relation.rb:471:in `load'
activerecord (4.0.0) lib/active_record/relation.rb:220:in `to_a'
activerecord (4.0.0) lib/active_record/relation/finder_methods.rb:325:in `find_first'
activerecord (4.0.0) lib/active_record/relation/finder_methods.rb:90:in `first'
activerecord-deprecated_finders (1.0.3) lib/active_record/deprecated_finders/relation.rb:129:in `first'
app/models/project.rb:27:in `recalc_spendings'
app/models/timesheet.rb:44:in `escalate_sums'
activesupport (4.0.0) lib/active_support/callbacks.rb:452:in `_run__1475279931726113629__save__callbacks'
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activerecord (4.0.0) lib/active_record/callbacks.rb:299:in `create_or_update'
activerecord (4.0.0) lib/active_record/persistence.rb:106:in `save'
activerecord (4.0.0) lib/active_record/validations.rb:51:in `save'
activerecord (4.0.0) lib/active_record/attribute_methods/dirty.rb:32:in `save'
activerecord (4.0.0) lib/active_record/transactions.rb:270:in `block (2 levels) in save'
activerecord (4.0.0) lib/active_record/transactions.rb:326:in `block in with_transaction_returning_status'
activerecord (4.0.0) lib/active_record/connection_adapters/abstract/database_statements.rb:202:in `block in transaction'
activerecord (4.0.0) lib/active_record/connection_adapters/abstract/database_statements.rb:210:in `within_new_transaction'
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activerecord (4.0.0) lib/active_record/transactions.rb:209:in `transaction'
activerecord (4.0.0) lib/active_record/transactions.rb:323:in `with_transaction_returning_status'
activerecord (4.0.0) lib/active_record/transactions.rb:270:in `block in save'
activerecord (4.0.0) lib/active_record/transactions.rb:281:in `rollback_active_record_state!'
activerecord (4.0.0) lib/active_record/transactions.rb:269:in `save'
app/controllers/timesheets_controller.rb:73:in `block in create'
actionpack (4.0.0) lib/action_controller/metal/mime_responds.rb:363:in `retrieve_collector_from_mimes'
actionpack (4.0.0) lib/action_controller/metal/mime_responds.rb:189:in `respond_to'
app/controllers/timesheets_controller.rb:72:in `create'
actionpack (4.0.0) lib/action_controller/metal/implicit_render.rb:4:in `send_action'
actionpack (4.0.0) lib/abstract_controller/base.rb:189:in `process_action'
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actionpack (4.0.0) lib/abstract_controller/callbacks.rb:18:in `block in process_action'
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actionpack (4.0.0) lib/action_controller/metal/rescue.rb:29:in `process_action'
actionpack (4.0.0) lib/action_controller/metal/instrumentation.rb:31:in `block in process_action'
activesupport (4.0.0) lib/active_support/notifications.rb:159:in `block in instrument'
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activesupport (4.0.0) lib/active_support/notifications.rb:159:in `instrument'
actionpack (4.0.0) lib/action_controller/metal/instrumentation.rb:30:in `process_action'
actionpack (4.0.0) lib/action_controller/metal/params_wrapper.rb:245:in `process_action'
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actionpack (4.0.0) lib/abstract_controller/base.rb:136:in `process'
actionpack (4.0.0) lib/abstract_controller/rendering.rb:44:in `process'
actionpack (4.0.0) lib/action_controller/metal.rb:195:in `dispatch'
actionpack (4.0.0) lib/action_controller/metal/rack_delegation.rb:13:in `dispatch'
actionpack (4.0.0) lib/action_controller/metal.rb:231:in `block in action'
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rack (1.5.2) lib/rack/etag.rb:23:in `call'
rack (1.5.2) lib/rack/conditionalget.rb:35:in `call'
rack (1.5.2) lib/rack/head.rb:11:in `call'
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actionpack (4.0.0) lib/action_dispatch/middleware/params_parser.rb:27:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/flash.rb:241:in `call'
rack (1.5.2) lib/rack/session/abstract/id.rb:225:in `context'
rack (1.5.2) lib/rack/session/abstract/id.rb:220:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/cookies.rb:486:in `call'
activerecord (4.0.0) lib/active_record/query_cache.rb:36:in `call'
activerecord (4.0.0) lib/active_record/connection_adapters/abstract/connection_pool.rb:626:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/callbacks.rb:29:in `block in call'
activesupport (4.0.0) lib/active_support/callbacks.rb:373:in `_run__1689713881852047757__call__callbacks'
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railties (4.0.0) lib/rails/application.rb:97:in `call'
rack (1.5.2) lib/rack/content_length.rb:14:in `call'
thin (1.6.1) lib/thin/connection.rb:82:in `block in pre_process'
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bin/rails:4:in `<top (required)>'
ruby-debug-ide (0.4.22) lib/ruby-debug-ide.rb:86:in `debug_program'
ruby-debug-ide (0.4.22) bin/rdebug-ide:110:in `<top (required)>'
-e:1:in `<main>'
I'm not really surprised by this message as the id is added to the query'result.
But why is it added by activerecord and how can I solve this?
Thanks!
EDIT
Thanks to PriteshJ, I understood that the ID was included by the "first" statement added at the end of my query to tell activerecord that it is a single record, not a collection.
So I know that I must get rid of first clause but when I do this, I get another error message:
NoMethodError: undefined method `total' for #<ActiveRecord::Relation::ActiveRecord_Relation_Timesheet:0x007fe73da50470>
from /usr/local/rvm/gems/ruby-2.0.0-p0/gems/activerecord-4.0.0/lib/active_record/relation/delegation.rb:121:in `method_missing'
This is normal because it is looking into a relation instead of a single record but I don't know how to solve it.
Should be simple though...

Answer 1

It looks like you are ordering the results by timesheets.id or you have some default order scope or somewhere you are adding a order.
Remove the ordering or add the column to select by which you are ordering the query.
UPDATE:
try using
self.timesheets.select("sum(total) as total, sum(quantity) as quantity").to_a.first
.first in activerecord will try to sort the query and pick first element so first by using .to_a take the result first then do .first

Answer 2

I think select is not the method you want to be using since you're not actually selecting a row in the db.
Perhaps sum is what you want (If I understand the problem correctly).
Would this work for you?:
total = project.timesheets.sum(:total)
quantity = project.timesheets.sum(:quantity)

Answer 3

With squeel gem, it is easy.
self.timesheets.select{[sum(:total).as(:total), sum(:quantity).as(:quantity)]}

Answer 4

self.timesheets.pluck("sum(total)", "sum(quantity)")

Answer 5

If you use select it will attempt to build a model with the fields you specified. You would be better of using pluck as suggested by jackpipe. However, I would make one alteration - methods like sum will return 0 if there are no records, but pluck will return nil, so to overcome that you could try this:
total, quantity = self.timesheets.pluck("sum(total)", "sum(quantity)").first.map(&:to_i)