活动记录查询和heroku问题。

Question

I'm simply trying to run a query to find all the records in a database that have a value in a "datetime" column that's less than the current unix timestamp.

Currently this is my code. It runs fine locally.

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

When I test this in the heroku console I get this error.

>> 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'

Any ideas?

Answer 1

You should be using a placeholder to get the right format and ensure that it is properly quoted:

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

You can't compare a timestamp column with an integer in PostgreSQL but you can in SQLite. You have to compare your timestamp with another timestamp (or date ) or a string that can be parsed as a timestamp . This SQL won't work:

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

but these will:

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

There are several lessons here:

1. You should also start developing on top of PostgreSQL if you're going to be deploying to Heroku, ActiveRecord will not insulate you from all of the differences between various databases.
2. You should let ActiveRecord worry about the type conversion issues as much as possible, if you're comparing against a date or a time, use a placeholder and hand AR a time object of some sort and let AR worry about it.
3. Use placeholders instead of string interpolation wherever possible.