Sql "in" query using active record

Rails
1

I’m trying to convert a non-sql application (4D or 4th Dimension) to
rails. Got all the CRUD stuff down, but I’m running into problem in
generating reports. 4D makes heavy use of Sets and Selections, which
are really just an array of record numbers that can be used to quickly
restore a query. Those arrays make aggregate reporting fairly easy. I
can get there using an sql query. I’m just looking for the best
approach using rails.

Lets say I have a simple has_many, belong_to relation:

Project:ARB (project fields :id, :name, "status, …)
has_many :tasks
Task:ARB (task fields :id, :project_id, :name, :date_due, …)
belong_to :project

I need to go both ways
give me a list of tasks where the project status is active, or:

select * from tasks where project_id in (select id from projects

where status = ‘Active’)

give me a list of projects where the task date_due is < some_date

select * from projects where id in (select project_id from tasks

where date_due < ‘2009-09-09’

How do I do that in an ActiveRecord find?

Steve

2

On Sep 10, 11:05 am, AppleII717 [email protected] wrote:

Project:ARB (project fields :id, :name, "status, …)
give me a list of projects where the task date_due is < some_date

select * from projects where id in (select project_id from tasks

where date_due < ‘2009-09-09’

How do I do that in an ActiveRecord find?

At a very basic level, the conditions option is just a blob of sql -
you can stick anything you want in there.

I personally would do the above as Project.find :all, :joins
=> :task, :conditions => [“due_date < ?”,…]

which isn’t the same sql but has (I believe) the same result

Fred

3

Thanks, you pointed my in the right direction. Not many examples
using :joins. I ended up with

Stage.find(:all, :joins => :job, :conditions => [“jobs.status = ? and
stages.name = ?”,“Active”,“Application”])

Which is my real life models where Jobs have many Stages.

Steve

On Sep 10, 6:31 am, Frederick C. [email protected]

4

AppleII717 wrote:

Thanks, you pointed my in the right direction. Not many examples
using :joins. I ended up with

Stage.find(:all, :joins => :job, :conditions => [“jobs.status = ? and
stages.name = ?”,“Active”,“Application”])

You may be able to rewrite this using the hash syntax for :conditions.
You might also want to look at named_scope and possibly
acts_as_state_machine.

Which is my real life models where Jobs have many Stages.

Steve

On Sep 10, 6:31�am, Frederick C. [email protected]

Best,

Marnen Laibow-Koser
http://www.marnen.org
[email protected]