PostgreSQL的導軌的has_many：通過/ collection_singular_ids /：順序問題

Question

在遷移到Heroku的過程中，我有一個奇怪的錯誤，只有當我使用PostgreSQL（在MySQL工作正常）

當我執行@user.county_ids我得到以下錯誤：

ActiveRecord::StatementInvalid: PGError: ERROR: for SELECT DISTINCT, ORDER BY expressions must appear in select list

LINE 1: ...id" WHERE ("activity_areas".user_id = 1) ORDER BY counties.n...

生成的SQL請求是：

SELECT DISTINCT "activity_areas".county_id FROM "activity_areas" INNER JOIN "counties" ON "counties"."id" = "activity_areas"."county_id" WHERE ("activity_areas".user_id = 1) ORDER BY counties.name ASC

終於型號：

class User < ActiveRecord::Base 
    has_many :activity_areas 
    has_many :counties, :through => :activity_areas 
end 

class ActivityArea < ActiveRecord::Base 
    belongs_to :user 
    belongs_to :county 

    default_scope joins(:county).order("counties.name ASC") 
end 

class County < ActiveRecord::Base 
    has_many :activity_areas 
    has_many :users, :through => :activity_areas 

    default_scope :order => 'name ASC' 
end 

關於如何解決此問題的任何想法？ 謝謝，

Answer 1

說到PostgreSQL，請確保order by子句中的元素也出現在select子句中。 MySQL是這個規則:)

試一試更改活動區域模型的默認範圍還挺寬以

default_scope select('counties.name').joins(:county).order("counties.name ASC") 

這應該產生這樣

SELECT DISTINCT "activity_areas".county_id, counties.name FROM "activity_areas"...