活动记录查询和heroku的问题.

Question

我只是尝试运行查询来查找数据库中的所有记录,这些记录的"datetime"列中的值小于当前的unix时间戳.

目前这是我的代码.它在当地运行良好.

t = Time.new.to_i
Event.where("datetime < #{t}")

当我在heroku控制台中测试它时,我收到此错误.

>> Event.where("datetime < #{t}")
ActiveRecord::StatementInvalid: PGError: ERROR:  operator does not exist: character varying < integer
LINE 1: SELECT "events".* FROM "events"  WHERE (datetime < 132462148...
                                                         ^
HINT:  No operator matches the given name and argument type(s). You might need to add explicit type casts.
: SELECT "events".* FROM "events"  WHERE (datetime < 1324621488)
    /app/.bundle/gems/ruby/1.9.1/gems/activerecord-3.1.1/lib/active_record/connection_adapters/postgresql_adapter.rb:1003:in `async_exec'
    /app/.bundle/gems/ruby/1.9.1/gems/activerecord-3.1.1/lib/active_record/connection_adapters/postgresql_adapter.rb:1003:in `exec_no_cache'
    /app/.bundle/gems/ruby/1.9.1/gems/activerecord-3.1.1/lib/active_record/connection_adapters/postgresql_adapter.rb:591:in `block in exec_query'
    /app/.bundle/gems/ruby/1.9.1/gems/activerecord-3.1.1/lib/active_record/connection_adapters/abstract_adapter.rb:244:in `block in log'

有任何想法吗？

Answer 1

您应该使用占位符来获取正确的格式并确保它被正确引用:

t      = Time.new
events = Event.where("datetime < :t", :t => t)

您无法timestamp在PostgreSQL中将列与整数进行比较,但您可以在SQLite中进行比较.您必须将您timestamp与另一个timestamp(或date)或可以解析为的字符串进行比较timestamp.这个SQL不起作用:

SELECT "events".* FROM "events" WHERE (datetime < 132462148)

但这些将:

SELECT "events".* FROM "events" WHERE (datetime < '2011-12-23 06:52:25.096869')
SELECT "events".* FROM "events" WHERE (datetime < '2011-12-23')

这里有几个教训:

1. 如果你要部署到Heroku,你也应该开始在PostgreSQL之上开发,ActiveRecord不会让你免受各种数据库之间的所有差异.
2. 您应该让ActiveRecord尽可能地担心类型转换问题,如果您要与日期或时间进行比较,请使用占位符并将AR作为某种时间对象,并让AR担心它.
3. 尽可能使用占位符代替字符串插值.