How to ignore duplicate inserts with datamapper

Question

I have a datamapper model that has a unique index on a property called name. I want to create new records when a name doesn't already exist and silently ignore attempts to create records with duplicate names. What's the "right" way to do this in datamapper?

Answer 1

One solution I came up with is simply to ignore the exception:

  begin
    Committer.create!(:name => committer)
  rescue DataObjects::IntegrityError => e # ignore duplicate inserts
  end

If you have a better (more idiomatic) way of doing it, please let me know.

Answer 2

The best approach is to use the dm-validations gem, and ensure that your name property is specified as being unique, eg:

class Committer
  include DataMapper::Resource

  # ... other properties ...

  property :name, String, :length => 1..100, :required => true, :unique => true
end

The dm-validations gem will introspect your model and automatically setup validations for your properties. In this case it won't allow more than one Committer to have the same name.

Answer 3

Here is another solution I came up with:

require 'dm-core'
require 'dm-validations'
require 'dm-more'
record = Committer.find_or_create(:name => committer)

If you're using this in sinatra, requiring dm-more seems to cause other problems. My solution was to require my own file that only contained the following code:

module DataMapper
 module Model
   def first_or_create(conditions = {}, attributes = {})
     first(conditions) || create(conditions.merge(attributes))
   end

   alias find_or_create first_or_create
 end
end

Answer 4

I think the best answer is to use first_or_create, which as Dan points out above, is already built into datamapper and therefore doesn't need to be declared.

require 'dm-core'
require 'dm-validations'

class Committer
  include DataMapper::Resource
  property :id, Serial
  property :name, String, :unique_index => true
  validates_present :name
  validates_is_unique :name
end
committer = "George"
record = Committer.first_or_create(:name => committer)