DataMapper Association Migrations

Question

I'm using Padrino with DataMapper, and I'm trying to make a migration for adding an association to a model. For example, I begin with this:

class User
  include DataMapper::Resource

  property :id, Serial
  property :name, String
end

class Post
  include DataMapper::Resource

  property :id, Serial
  property :title, String
  property :body, Text
end

class Comment
  include DataMapper::Resource

  property :id, Serial
  property :name, String
end

And I end with the following:

class User
  include DataMapper::Resource

  property :id, Serial
  property :name, String

  has n, :posts
end

class Post
  include DataMapper::Resource

  property :id, Serial
  property :title, String
  property :body, Text

  belongs_to :user
  has n, :comment
end

class Comment
  include DataMapper::Resource

  property :id, Serial
  property :name, String

  belongs_to :post
end

I already have the migration for creating the three tables, but I do not for adding the associations. What would the code be for creating the migration for the associations?

score 2 · Accepted Answer · answered Jan 10 '11 at 09:08

2

DataMapper.auto_upgrade! will add new FK properties

answered Jan 10 '11 at 09:08

solnic

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19

Thanks, I thought I had to add a migration first. – Ethan Turkeltaub Jan 12 '11 at 19:17

score 1 · Answer 2 · answered Jul 25 '11 at 19:17

auto_upgrade is nice, but won't allow incremental step back.

migration 3, :create_products do
  up do
    modify_table :post do
      add_column :user_id, Integer
    end
    modify_table :comment do
      add_column :post_id, Integer
    end
  end

  down do
    modify_table :post do
      drop_column :user_id, Integer
    end
    modify_table :comment do
      drop_column :post_id, Integer
    end
  end
end

that's it.

DataMapper Association Migrations

2 Answers2