ruby-on-rails - postgresql 中的“Where-in”查询显示相同结果的两个不同查询

Question

我有如下的事件记录关联关系。

@tasks =  #<ActiveRecord::AssociationRelation [#<Task id: 3130, title: "Commit to at least one small win today", content: "When I check-in on the app it lets me acknowledge m...",created_at: "2016-01-13 01:36:15", updated_at: "2016-01-13 04:47:57", state: "active", #<Task id: 3131, title: "Purposefully walk 3 minutes ", content: "More than just my ordinary day, I choose 5 minutes ...", created_at: "2016-01-13 04:52:32", updated_at: "2016-01-13 04:56:22", state: "active", #<Task id: 3132, title: "1km Walk or Run by Sunday", content: "I pick a direction, start with a 10 minute warm up,...", created_at: "2016-01-13 04:56:05", updated_at: "2016-01-13 04:56:05", state: "active",#<Task id: 3249, title: "1km Walk or Run by Wednesday", content: "I pick a direction, start with a 10 minute warm up,...", created_at: "2016-01-24 23:23:34", updated_at: "2016-01-24 23:23:34", state: "active"]> 


@array = []

@tasks.each do |task|
if (condition)
  @array << task.id
end  

@tasks = @tasks.where.not('tasks.id in (?)',@array)

如果我在@array 中得到任何非空值，
上述条件工作正常。

如果我得到@array = [] i,e 空数组，
@tasks = @tasks.where.not('tasks.id in (?)',@array) 没有给我正确的结果。

此外，@tasks = @tasks.where('tasks.id in (?)',@array)，当数组为 [] 时，通过删除 'not' 给出相同的结果p>

 @habits = @habits.where.not('habits.id in (?)',@id_s)  ====> output => []
 @habits = @habits.where('habits.id in (?)',@id_s)  ====> output => []

They both are returning same optput if @id_s is []

为什么这些查询针对两种不同的条件返回相同的值？

Answer 1

如果您的 Rails 版本是最新的，您应该切换到哈希表示法，它可以为您处理所有特殊情况，例如空数组:

@tasks = @tasks.where.not(id: @array)