Question

Whatever columns/types/relations i’m using within my DataMapper models i’m always get same fatal error:

undefined method `include?' for nil:NilClass

a sample model:

class Book
  include DataMapper::Resource

  property :id, Serial
  property :name, String
end

Even with this trivial model i get that weird error.

Latest datamapper, reinstalled to be sure it is no broken somehow.
Ruby 1.9.3
Mysql 5

Sequel works just well on same environment.

Answer 1

did you call DataMapper.finalize after defining your models?

try:

class Book
  include DataMapper::Resource

  property :id, Serial
  property :name, String
end

DataMapper.finalize # this is required on any scenario

Official docs:
http://datamapper.org/getting-started.html

See Finalize Models at the bottom