Rails - May 2006 - ActiveRecord collection_select and has_and_belongs_to_many

Hello everyone, first post to the list and a relative newbie to Rails
development. Done quite a bit of JSP, PHP, HTML, XML etc and thought I would
kick the tires on Rails to see if it can speed up development for internal
applications. Anyway, I am running into a problem that is just driving me
crazy and everything I read on the net doesn''t seem to help. I was
hoping
someone here might have had the same problem and be able to point me in the
right direction.
 
Database Schema:
 
table employees
    id
    name
 
table projects
    id
    name
 
table project_roles
    id
    name
 
table project_members
    id
    employee_id
    project_id
    role_id
 
I then have the following ActiveRecord objects:
 
class Employee < ActiveRecord::Base
  has_and_belongs_to_many :project_members, :join_table =>
"project_members", :class_name => "ProjectMember"
end

class Project < ActiveRecord::Base
  has_and_belongs_to_many :project_members, :join_table =>
"project_members", :class_name => "ProjectMember"
end

class ProjectRole < ActiveRecord::Base
  has_and_belongs_to_many :project_members, :join_table =>
"project_members", :class_name => "ProjectMember"
end

class ProjectMember < ActiveRecord::Base
  belongs_to :project
  belongs_to :employee
  belongs_to :project_role
  set_table_name "project_members"
end

The next thing I want to do is to display a multi-select list box, on the
project form, and display all of the employees that when selected will add
the proper entries into the project_members table. I would be happy to write
a method that gets called on submission and transforms the @params into the
appropriate ActiveRecord requests, but I cannot get the list to display with
collection_select no matter what I try.

Can someone point me in the right direction? Am I using the
has_and_belongs_to_many relationship wrong? Is it useless to try to get this
kind of a relationship to show up using collection_select? Is there some
other parameters that I need to use that I am not? Is there a better pattern
for these type of relationships with regards to integrating them into the
MVC paradigm?

Any help would be appreciated as I am Googled out!

Keith

You might wan to have a look at through associations for this: 
http://wiki.rubyonrails.com/rails/pages/ThroughAssociations.

I''ve also found that using checkboxes is easier for habtm
relationships.
Take the following relationship:

class Project < ActiveRecord::Base
   has_and_belongs_to_many :members
end

class Member < ActiveRecord::Base
   has_and_belongs_to_many :projects
end

Your ''edit member'' view might show a list of checkboxes for
each project:

<% for project in @projects %>
   <%=check_box_tag name="member[project_ids]",
                    project.id,
                    @member.projects.include?(project) %>
<% end %>

When this is submitted rails will automatically update the joiner table 
with the checked associations.

Also, I might be wrong in your case, but you shouldn''t have to specify 
all the table data in your models - Rails will pick all that up for you. 
  For example:

Take the following tables:
parents
children

You models will look like this:

class Parent < ActiveRecord::Base
   has_many :children
end

class Child < ActiveRecord::Base
   belongs_to :parent
end

Rails will do all the hard work for you.

Wow - i really got going on that reply :0)

Hope it helps,

Steve


Keith Bottner wrote:
> Hello everyone, first post to the list and a relative newbie to Rails
> development. Done quite a bit of JSP, PHP, HTML, XML etc and thought I
would
> kick the tires on Rails to see if it can speed up development for internal
> applications. Anyway, I am running into a problem that is just driving me
> crazy and everything I read on the net doesn''t seem to help. I was
hoping
> someone here might have had the same problem and be able to point me in the
> right direction.
>  
> Database Schema:
>  
> table employees
>     id
>     name
>  
> table projects
>     id
>     name
>  
> table project_roles
>     id
>     name
>  
> table project_members
>     id
>     employee_id
>     project_id
>     role_id
>  
> I then have the following ActiveRecord objects:
>  
> class Employee < ActiveRecord::Base
>   has_and_belongs_to_many :project_members, :join_table =>
> "project_members", :class_name => "ProjectMember"
> end
> 
> class Project < ActiveRecord::Base
>   has_and_belongs_to_many :project_members, :join_table =>
> "project_members", :class_name => "ProjectMember"
> end
> 
> class ProjectRole < ActiveRecord::Base
>   has_and_belongs_to_many :project_members, :join_table =>
> "project_members", :class_name => "ProjectMember"
> end
> 
> class ProjectMember < ActiveRecord::Base
>   belongs_to :project
>   belongs_to :employee
>   belongs_to :project_role
>   set_table_name "project_members"
> end
> 
> The next thing I want to do is to display a multi-select list box, on the
> project form, and display all of the employees that when selected will add
> the proper entries into the project_members table. I would be happy to
write
> a method that gets called on submission and transforms the @params into the
> appropriate ActiveRecord requests, but I cannot get the list to display
with
> collection_select no matter what I try.
> 
> Can someone point me in the right direction? Am I using the
> has_and_belongs_to_many relationship wrong? Is it useless to try to get
this
> kind of a relationship to show up using collection_select? Is there some
> other parameters that I need to use that I am not? Is there a better
pattern
> for these type of relationships with regards to integrating them into the
> MVC paradigm?
> 
> Any help would be appreciated as I am Googled out!
> 
> Keith
> 
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>