create unique constraints per user in tables with n:m relation - ruby

Question

I have asked a question a few moments ago, create unique constraints per user and the answer was very simple.
For creating a unique index on a column, but on a per user basis, all I have to do is:
unique [:user_id, :name] # SQL syntax: UNIQUE (user_id, name)
But the relation between the user table and the table that references the user_id is a 1:n (user to location), so I have a foreign_key inside the location table which references user_id. This question is about a n:m relation between two tables and adding a unique constraint on one of the tables.
Sequel.migration do
change do
Sequel::Model.db.run 'CREATE EXTENSION IF NOT EXISTS "uuid-ossp"'
create_table :customer do
String :id, :type => :uuid, :primary_key => true, :default => Sequel.function(:uuid_generate_v4)
DateTime :created_at
DateTime :updated_at
index :id, :unique => true
end
end
end
Sequel.migration do
change do
Sequel::Model.db.run 'CREATE EXTENSION IF NOT EXISTS "uuid-ossp"'
create_table :role do
String :id, :type => :uuid, :primary_key => true, :default => Sequel.function(:uuid_generate_v4)
String :name, :unique => true, :null => false # TODO: unique, per customer
DateTime :created_at
DateTime :updated_at
unique [:customer_id, :name]
index :id, :unique => true
full_text_index :name, :index_type => :gist
end
end
end
The above code illustrates the two tables I mentioned have a n:m relation (customer to role), the following table illustrates the join table with the foreign keys for both the tables:
Sequel.migration do
change do
Sequel::Model.db.run 'CREATE EXTENSION IF NOT EXISTS "uuid-ossp"'
create_table :customer_role do
String :id, :type => :uuid, :primary_key => true, :default => Sequel.function(:uuid_generate_v4)
foreign_key :customer_id, :customer, :type => :uuid
foreign_key :role_id, :role, :type => :uuid
index :id, :unique => true
end
end
end
What I would like to do is to declare a unique constraint such as UNIQUE (customer_id, :name) on the role table. But I cannot do that, so how do I achieve that in another way?

Answer 1

What I would like to do is to declare a unique constraint such as
UNIQUE (customer_id, :name) on the role table. But I cannot do that,
so how do I achieve that in another way?
The essence of your problem seems to be that the column role.customer_id doesn't exist. In fact, I'm pretty sure that column shouldn't exist, so that part's actually good.
At the very least, you need
unique [:customer_id, :role_id]
in "customer_role".