datamapper multi-field unique index

Question

In Datamapper, how would one specify the the combination of two fields must be unique. For example categories must have unique names within a domain:

class Category
  include DataMapper.resource
  property :name, String, :index=>true #must be unique for a given domain

  belongs_to :domain
end

Councilwoman

Somewhere I saw mentioned that named keys will group like this. ie :unique_index=>:name for both name and domain. – Councilwoman

Answer 1

Did you try to define both properties as keys? Not sure I have tried it but that way they should become a composite key.

property :name, String, :key => true    
property :category, Integer, :key => true

Exacerbate

Actually there already is a key, I just didn't include it in the code snippet. – Councilwoman

Answer 2

You have to create a unique index for the two properties:

class Category
  include DataMapper::Resource

  property :name, String, :unique_index => :u
  property :domain_id, Integer, :unique_index => :u

  belongs_to :domain
end

Heterogony

This is incorrect as it will require that both name and domain be unique across the table. What I asked was how to make the set (:name, :domain) unique. – Councilwoman

Indeed, although the :u symbol could have been clearer -- for example :index_on_name_and_domain_id -- it actually is correct. See the section Indices on the DataMapper property documentation page: rubydoc.info/github/datamapper/dm-core/master/DataMapper/…. The statements create a multi-column composite unique index. – Desired

Answer 3

Actually, John, Joschi's answer is correct: the use of named :unique_index values does create a multiple-column index; it's important to read the right-hand side of those hash-rockets (i.e., if it had just been true, you would be right).

Dawna

I've moved away from DataMapper so this may have changed, but at the time I wrote the comment, it was correct. – Councilwoman