Dbase query performance vs. iterating over large result arra

Rails
1

Hello Folks. Please excuse my beginner’s ignorance …

My question regards database query performance vs. iterating over
nested results in an array. In the example below, a Project has many
Tasks. Tasks have a due date. When I display Projects, I would like to
also display the cumulative delay for all open Project Tasks based on
their due date, and today’s date.

Something like …

Project | Delay
XYZ | 5 days (4 tasks late, 1.25 day average delay)
… 100 records

As I learn RoR, I’ve discovered a couple ways I can do this. I can
perform the calculations in a single query. I can use the :include
option to build an array with nested children, and iterate over each
Project’s Tasks with something like parent.child.each.do. Or, finally,
I can issue 100 queries to the database, once for each record. Each
has advantages, but which is the most commonly accepted method in the
RoR community?

Thanks in advance

John

2

Astorian wrote:

Project | Delay
XYZ | 5 days (4 tasks late, 1.25 day average delay)
… 100 records

As I learn RoR, I’ve discovered a couple ways I can do this. I can
perform the calculations in a single query. I can use the :include
option to build an array with nested children, and iterate over each
Project’s Tasks with something like parent.child.each.do. Or, finally,
I can issue 100 queries to the database, once for each record. Each
has advantages, but which is the most commonly accepted method in the
RoR community?

Doing 100 queries to the database sounds like a bad idea. There’s no
reason not to use :include in the example given. Try doing it both ways
and see the difference in execution time for yourself.

–
Cheers,

  • Jacob A.