ruby-on-rails-3 - PostgreSQL Rails has_many :through/collection_singular_ids/:order problem

Question

在迁移到heroku的过程中，只有在使用PostgreSQL时出现奇怪的错误(在Mysql中工作正常)

当我执行 @user.county_ids 时，出现以下错误:

ActiveRecord::StatementInvalid: PGError: ERROR: 对于 SELECT DISTINCT，ORDER BY 表达式必须出现在选择列表中

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

生成的sql请求是:

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县名 ASC

最后是模型:

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

知道如何解决这个问题吗？谢谢，

Answer 1

对于 PostgreSQL，确保 order by 子句中的元素也存在于 select 子句中。 MySQL 对这条规则有点宽容:)

尝试将事件区域模型中的默认范围更改为

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

这应该生成类似的 SQL

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