How to set up this model :

Hello,
I have a nice case for active record experts :0)

i have the following situation:
I have: customers users and groups and an acccess table which determines
what group has access to what customer:

this is what i have in my current (php) application

customers:
id
name

users
id
name

groups
id
name

groupmemberships
id
user_id
group_id

accessrights
id
group_id
customer_id

if someone wants to see all of his customers, i perform this query:

select … from customers where customer.id=accessrights.customer_id
and accessrights.group_id=groupmemberships.group_id and
groupmemberships.user_id=$currentuser

i guess i can do something simular in rails, but are there better
methods utilising active record?

regards,

Remco

remco wrote:

Hello,
I have a nice case for active record experts :0)

i have the following situation:
I have: customers users and groups and an acccess table which determines
what group has access to what customer:

this is what i have in my current (php) application

customers:
id
name

users
id
name

groups
id
name

groupmemberships
id
user_id
group_id

accessrights
id
group_id
customer_id

if someone wants to see all of his customers, i perform this query:

select … from customers where customer.id=accessrights.customer_id
and accessrights.group_id=groupmemberships.group_id and
groupmemberships.user_id=$currentuser

i guess i can do something simular in rails, but are there better
methods utilising active record?

This is a job for has_many :through. You’ll want to create join model
classes that embody the relationships between the other models. I’d name
them Membership and Permission.

class Membership < ActiveRecord::Base
belongs_to :group
belongs_to :user
end

class Right < ActiveRecord::Base
belongs_to :group
belongs_to :customer
end

class Group < ActiveRecord::Base
has_many :memberships
has_many :users, :through => :memberships
has_many :rights
has_many :customers, :through => :rights
end

class User < ActiveRecord::Base
has_many :memberships
has_many :groups, :through => :memberships
end

class Customer < ActiveRecord::Base
has_many :rights
has_many :groups, :through => :rights
end

You can get all of a users customers using associations and some Ruby:

User

def customers
self.groups.collect {|group| group.customers}.flatten.uniq
end

Or you can use some SQL:

User

def customers
Customer.find(:all, :readonly => false,
:joins => “INNER JOIN rights ON customers.id = rights.customer_id
INNER JOIN memberships ON rights.group_id = memberships.group_id”
:conditions => [“memberships.user_id = ?”, self]
end


Josh S.
http://blog.hasmanythrough.com

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