rails sum多个字段
我试图在rails中做这个假设简单的操作：
self.timesheets.select("sum(total) as total, sum(quantity) as quantity").first where self is a project 当我在控制台模式下执行它时，它可以工作，但它呈现3列：
[#]
当我在应用程序中运行它时，我收到此错误消息：
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' activerecord (4.0.0) lib/active_record/connection_adapters/abstract_adapter.rb:420:in `log' 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' activesupport (4.0.0) lib/active_support/callbacks.rb:80:in `run_callbacks' 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) 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我对此消息并不感到惊讶，因为id被添加到查询结果中。
但是为什么它是由activerecord添加的，我该如何解决这个问题呢？
谢谢！
编辑
感谢PriteshJ，我理解ID在我的查询结尾处添加的“第一个”语句中包含，告诉activerecord它是单个记录，而不是集合。
所以我知道我必须摆脱第一个条款但是当我这样做时，我得到另一个错误信息：
NoMethodError: undefined method `total' for # 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'
这是正常的，因为它正在研究关系而不是单个记录，但我不知道如何解决它。
虽然应该很简单……
看起来您是按timesheets.id订购结果，或者您有一些默认订单范围或您正在添加订单的地方。
删除顺序或添加列以选择您按顺序排序查询。
更新：
尝试使用
self.timesheets.select("sum(total) as total, sum(quantity) as quantity").to_a.first
.first in activerecord将尝试对查询进行排序并首先选择第一个元素，然后首先使用.to_a获取结果，然后执行.to_a
我认为select不是你想要使用的方法，因为你实际上没有在db中选择一行。
也许sum就是你想要的（如果我理解正确的问题）。
这对你有用吗？：
total = project.timesheets.sum(:total) quantity = project.timesheets.sum(:quantity)
有吱吱嘎吱的gem，很容易。
self.timesheets.select{[sum(:total).as(:total), sum(:quantity).as(:quantity)]}
self.timesheets.pluck("sum(total)", "sum(quantity)")
如果使用select ，它将尝试使用您指定的字段构建模型。 你应该更好地使用jackpipe建议的采摘。 但是，我会进行一次更改 – 如果没有记录， sum方法将返回0，但是pluck将返回nil，所以要克服它你可以试试这个：
total, quantity = self.timesheets.pluck("sum(total)", "sum(quantity)").first.map(&:to_i)