Rails - Jul 2012 - advanced AR: select+include OR manual eager load OR virtual-column SQL - howto?

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

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On Tuesday, July 17, 2012 1:39:54 PM UTC+1, Ruby-Forum.com User
wrote:
>
> 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
 
> 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 
>
> -- 
> Posted via http://www.ruby-forum.com/. 
>
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