Deleting all records in a database table

How do I delete all records in one of my database tables in a Ruby on Rails app?

If you are looking for a way to it without SQL you should be able to use delete_all.

Post.delete_all

or with a criteria

Post.delete_all "person_id = 5 AND (category = 'Something' OR category = 'Else')"

See here for more information.

The records are deleted without loading them first which makes it very fast but will break functionality like counter cache that depends on rails code to be executed upon deletion.

To delete via SQL

Item.delete_all # accepts optional conditions

To delete by calling each model's destroy method (expensive but ensures callbacks are called)

Item.destroy_all # accepts optional conditions

All here

if you want to completely empty the database and not just delete a model or models attached to it you can do:

rake db:purge

you can also do it on the test database

rake db:test:purge

If you mean delete every instance of all models, I would use

ActiveRecord::Base.connection.tables.map(&:classify)
  .map{|name| name.constantize if Object.const_defined?(name)}
  .compact.each(&:delete_all)

BlogPost.find_each(&:destroy)

If your model is called BlogPost, it would be:

BlogPost.all.map(&:destroy)

More recent answer in the case you want to delete every entries in every tables:

def reset
    Rails.application.eager_load!
    ActiveRecord::Base.descendants.each { |c| c.delete_all unless c == ActiveRecord::SchemaMigration  }
end

More information about the eager_load here.

After calling it, we can access to all of the descendants of ActiveRecord::Base and we can apply a delete_all on all the models.

Note that we make sure not to clear the SchemaMigration table.