sql - Ruby on Rails : Finding the sum of a column in a returned search query

Question

我正在尝试查找名为 length 的列的总和，这是一个简单的整数列，其中包含每条记录持续的秒数。

我有一个搜索表单设置来查询数据库以获取我在 Controller 中设置的某些条件:

@time_entries = TimeEntry.find(:all, :conditions => [ "(user_id = ?) AND (projecttitle LIKE ?) AND (date BETWEEN ? AND ?)", current_user, '%'+params[:projecttitle]+'%', @startdate, @enddate ])

然后我用不起作用的代码跟踪该查询，尝试对 length 求和我返回的查询的列...

@total_time = @time_entries.sum(:length)

然后当我用 <%= @total_time %> 在我的 View 中渲染它时，我收到此错误:

undefined method '+' for #<TimeEntry:0x007ffdbbd45b78>

有什么想法吗？非常感谢您的帮助:)

Answer 1

改变

@total_time = @time_entries.sum(:length)

至

@total_time = @time_entries.sum(&:length)

仅供引用，如果您只需要一列来操作，请在查询中使用 :select 子句，例如

@time_entries = TimeEntry.find(:all, :select => 'length', 
                  :conditions => [ "(user_id = ?) AND (projecttitle LIKE ?) 
                           AND (date BETWEEN ? AND ?)", current_user, 
                           '%'+params[:projecttitle]+'%', @startdate, @enddate ])

如果您只需要表中某些列的总和，您可以使用 sum方法如

@total_time = TimeEntry.sum(:length, 
                  :conditions => [ "(user_id = ?) AND (projecttitle LIKE ?) 
                           AND (date BETWEEN ? AND ?)", current_user, 
                           '%'+params[:projecttitle]+'%', @startdate, @enddate ])