了解活动记录查询

Question

I needed to do some complex subquery for a project i am working on. I could't figure out how to do it in plain active record. I tried several things and ended up opting for generic SQL query using

ActiveRecord::Base.connection.exec_query(
  "
  SELECT gid as id, (dp).path, (dp).geom, ST_AsText((dp).geom),  ST_X((dp).geom) as longitude, ST_Y((dp).geom) as latitude
  FROM (
  SELECT gid, ST_DumpPoints(ST_AsText(ST_Transform(geom, 4326))) as dp
  FROM apples
  WHERE gid in (#{@object.id})
  ) AS GEO;
  "
)

Here i am selecting from a subquery and transforming geometry to Points using plain postgresql. If i were to do it in ActiveRecord queries, how do i do it? Is this type of query even possible in ActiveRecord?

Answer 1

ActiveRecord does not provide you with anything fancy. You can perform simple stuff, but when there's a need for a complex query you just go with plain SQL as you did.

You can check Arel which might give you more flexibility. But still, in the end, I think, it's not worth - it won't be as effective as a native query.

Do simple stuff with ORM. Do complex stuff with plain SQL.