[Rails] Query on many to many relation

[Van Aken Martin (GFDI)]

Thanks already, Victor.
I see that I must be a little more precise about my problem.
The condition of being an employee of the given company is only one
among a series of other.

>From your proposal, I could without problem fetch all employees from the
given company, then apply my other criteria.

But doing so would be very static (I construct my multi-criteria query
dynamically), and would require to load from the DB a lot of records I
don't need.

For example, one of my (possible) criteria is being part of a team, and
my code is :

if(team_key != '')
			list << team_key
			query << " AND " unless query == ""
			query << "team_id = ?"
end

But I can't find a way to express a many-to-many relationship (employee
to team is many-to-one).

I hope I'm a little more clear now. I'm pretty sure I'm not the first to
stumble on this kind of situation (multicriteria search with many to
many relation).

Thanks in advance.

Martin
-----Original Message-----
From: rails-bounces at lists.rubyonrails.org
[mailto:rails-bounces at lists.rubyonrails.org] On Behalf Of Victor
Jalencas
Sent: Tuesday, January 25, 2005 9:51 AM
To: rails at lists.rubyonrails.org
Subject: Re: [Rails] Query on many to many relation

Martin, you could do this:

  company=Company.find(company_id)
  company.employees

The last expression will return you the list of employees. All the hard 
works is done by Rails behind the scenes


cheers

Victor

Van Aken Martin (GFDI) wrote:
> Hello all,
> 
> I'm starting to develop a small application using rails, with great 
> success (and pleasure) until now.
> 
> I've stumbled on a very simple problem, but I can't find any 
> documentation on this :
> 
>  
> 
> I've have two classes with a "has_and_belong_to_many" relation (and so

> three tables). For simplicity, I will name them "employee" and
"company".
> 
> I would like to make a find to retrieve all employees who are employed

> in a given company.
> 
>  
> 
> Something like : Employee.find_all([company = ?],company_id)
> 
>  
> 
> How can I reference the join table to make this work ?
> 
> The SQL would be something like :
> 
>  
> 
> Select Employees.* from Employees, Companies, Companies_Employees
where
> 
> Companies.id = 
> company_id                                                     //where
> 
> AND Companies.id = Companies_Employees.Company_id         //join
> 
> AND Emploees.id = Companies_Employees.Employee_id          //join
> 
>  
> 
> But, if possible, I would like to avoid the "find_by_sql"
> 
>  
> 
> Thanks for any help, and please forgive me for my English,
> 
>  
> 
> Martin Van Aken
> 
> 
>
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