advanced AR: select+include OR manual eager load OR virtual-column SQL - howto?

rubyonrails-talk
1

Hi there,

I figured out, that .includes() kills .select(). That means you can not specify virtual column, like select('SUM(points) AS points') with eager loading.

So how you can accomplish this task? Eager loading + select ?

Ok, this is our case:

We are selecting 'players'. player belongs to 'sportsman', which has column called 'name', this column we want to eager load in following statement. We are suming column 'points' from has_many :events association as our desired virtual column.

Player.joins('LEFT OUTER JOIN events ON players.id = events.player_id').joins('LEFT OUTER JOIN sportsmen ON players.sportsman_id = sportsmen.id').select('players.*, sporsmen.name, SUM(points) AS points').group('players.id').order('sportsmen.name DESC')

Suggestion:

Is there some convention what to write to .select() to eager load. If i write select('players.*, sportsmen.name, SUM(points) AS points), it loads sportsman.name lazily anyways (so it loads it twice).

Or its possible throught AREL?

Do you understand what I mean? To use eager loading with virtual column.

Thanks, I was fighting with this all the yesterday, learning a lot from AR, but with still no success in this case.

Thanks hackers,

rndrfero

2

Hi there,

I figured out, that .includes() kills .select(). That means you can not

specify virtual column, like select(‘SUM(points) AS points’) with eager

loading.

So how you can accomplish this task? Eager loading + select ?

Do you really need eager load or is preloading ok. preloading doesn’t conflict with select.

A long long time ago I wrote a plugin to tack this onto rails 2.x but obviously none of that applies with rails 3. It looks to me that the method to poke at would be construct_relation_for_association_find(join_dependency)

Fred