has_and_belongs_to_many Problem

rubyonrails-talk
1

Hi all

I'm having a problem with has_and_belongs_to_many (habtm)...

Here is my setup:

tables: customers, customergroups and a join-table called customers_customergroups

customers has an id as pk and so does customergroups. the join table has customer_id and customergroup_id (as well as an id)

both models include the habtm statement, one with :customergroups and the other with :customers

No I do the following:

customer = Customers.find(123)

at this point i would like to say: customer.customergroups.to_xml.

The error message I get here is: uninitialized constant Customers::Customergroup

What am I doing wrong? Can anyone help?

2

Try changing the name of the join table to customergrous_customers. Also with a straight habtm the join table doesn't need an ID column, though I don't know off hand if it breaks anything to have one.

3

I already switched both parts to customergroups_customer, no effect. I now did remove the id column, because I don't really need it, but still no luck.

4

The join table should be called customergroups_customers (notice the s on the end of customers) and should have 2 columns customer_id and customergroup_id their should be no primary key or any other column.

in your customer.rb file you should have as the second line   has_and_belongs_to_many :customergroups

and in your customergroup.rb file you should have   has_and_belongs_to_many :customers

(notice the models have singular names and the associations have pluralised names)

5

Actually I'm pretty sure that the default table name would be customers_customergroups It get's generated by the sort order of the (singular) class names and "customer" < "customergroup"

Of course it can be explicitly set using the :join_table option on the :has_and_belongs_to_many relationship.

6

Personally I've ditched habtm and the general drift in Rails development is to avoid it. If you use an explicit join table it's a little easier to manage (IMO) and you gain the benefit of easily handling attributes on the association. Just to reduce the long names I'd use something like this:

Customer (as is) CustomerGroup (as is) GroupMembership (customer_id, customer_group_id)

Customer has_many :group_memberships has_many :customer_groups, :through :group_memberships

GroupMembership belongs_to :customer belongs_to :customer_group

CustomerGroup has_many :group_memberships has_many :customers, :through :group_memberships