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We are working on rails engine on 3.2.9. Engine is generated with :

rails plugin new rails_engine -mountable --skip-test-unit --dummy-path=spec/dummy

After initial setup, we can generate a model just like what we do in regular rails app:

rails g model post name:string

There is a migration file created under db/migrate/. Next we did db:migrate under the/ rails_engine :

rake db:migrate

It causes error: 

Don't know how to build task 'db:migrate'

List available rake tasks:

bundle exec rake --tasks
rake build         # Build test_itemx-0.0.1.gem into the pkg directory
rake clobber_rdoc  # Remove RDoc HTML files
rake install       # Build and install test_itemx-0.0.1.gem into system gems
rake rdoc          # Build RDoc HTML files
rake release       # Create tag v0.0.1 and build and push test_itemx-0.0.1.gem to Rubygems
rake rerdoc        # Rebuild RDoc HTML files

There is no db:migrate among them. The question is how to load db tasks back to rake.

user938363
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  • `bundle exec rake db:migrate` by any chance? – MrYoshiji Nov 14 '12 at 22:02
  • No difference with bundle exec. Tried to run rake db:migrate under spec/dummy and it went through without throwing up error. However schema.rb under /spec/dummy/db/ is still empty. Something is not right here. – user938363 Nov 14 '12 at 22:19
  • skip-test-caused the problem. To enable rake db:migrate in engine root directory, the engine needs to be created with: rails plugin new my_engine --mountable --spec-path=spec/dummy – user938363 Nov 15 '12 at 22:12

2 Answers2

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This is the expected behavior. Remember that it is a mountable engine. It does not have an environment of it's own. You need to mount it to a Rails application (Not an engine but an actual app). Engine does not have any database. It uses the database defined in its parent app in which it is mounted. So obviously your db:migrate would not work.

Do the following in your parent app for an engine:

  1. Mount your engine in the Gemfile of a rails application as just another engine using :path or :git option

    gem 'engine_name', :path=>'path/to/engine/directory'

  2. bundle install

  3. rake engine_name:install:migrations

  4. rake db:migrate

atmaish
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I've entered spec/dummy in my engine folder and just runned rake db:migrate plus the same for test Env, and db/schema.rb was added. But I had to add spec/dummy/db folder manually before.

Artur79
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