How do I override rake tasks for a custom database adapter?

问题

I've written a custom database adapter that works correctly and effectively when a rails server is running. I would now like to add the usual rake task definitions for creating, dropping and migrating the database.

I would like to implement:

db:[drop|create|migrate]

How do I package these definitions with my gem so that they override the default ones for anyone who uses the gem?

I looked through the source of other adapters but all the rake task logic appears to be baked into active_record itself, each task just switches on the adapter name.

回答1:

This is possible with:

# somewhere in your gem's tasks
Rake::Task['db:create'].clear

# then re-define
namespace 'db' do
  task 'create' do
    # ...
  end
end

When Take::Task#[] can't resolve a task it will fail. If your tasks sometimes exists, you might want to:

task_exists = Rake.application.tasks.any? { |t| t.name == 'db:create' }
Rake::Task['db:create'].clear if task_exists

If you want to add tasks to an existing rake task, use enhance.

Rake::Task['db:create'].enhance do
  Rake::Task['db:after_create'].invoke
end

回答2:

You can write

Rake::Task['db:create'].clear

to delete the original task before redefining it. Also check out Overriding rails' default rake tasks

来源：https://stackoverflow.com/questions/6205968/how-do-i-override-rake-tasks-for-a-custom-database-adapter