如何在Rails查询的WHERE子句中编写DateTime.current？

Question

In one of my models I have a column called started which is a DateTime, and I want to be able to write a class method that would return the records which difference between DateTime.current and started column is bigger than N seconds.

Here is what I have so far:

def self.elapsed_started_bigger_than(sec = 10)
  where('started IS NOT NULL').
  where( ((DateTime.current - started) * 24 * 60 * 60).to_i > sec) # This is what I don't know how to write
end

Ideally this should be database engine agnostic, even though right now I am using PostgreSQL.

Answer 1

You should use a scope and write it like this

scope :started, where('started IS NOT NULL')

scope :elapsed_since, Proc.new {|sec| where("NOW() - started > ?", sec.seconds)}

Use it like this

model.started.elapsed_since(10)

EDIT

Mysql

` mysql> select NOW() - 10;

+-----------------------+

| NOW() - 10 |

+-----------------------+

| 20140707200211.000000 |

+-----------------------+

mysql> select NOW() - "10";

+----------------+

| NOW() - "10" |

+----------------+

| 20140707200223 |

+----------------+

`