How to list of all the tables defined for the database when using active record?

Call ActiveRecord::ConnectionAdapters::SchemaStatements#tables. This method is undocumented in the MySQL adapter, but is documented in the PostgreSQL adapter. SQLite/SQLite3 also has the method implemented, but undocumented.

>> ActiveRecord::Base.connection.tables
=> ["accounts", "assets", ...]

See activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb:21, as well as the implementations here:

• activerecord/lib/active_record/connection_adapters/mysql_adapter.rb:412
• activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb:615
• activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb:176

Based on the two previous answers, you could do:

ActiveRecord::Base.connection.tables.each do |table|
  next if table.match(/\Aschema_migrations\Z/)
  klass = table.singularize.camelize.constantize      
  puts "#{klass.name} has #{klass.count} records"
end

to list every model that abstracts a table, with the number of records.

It seems like there should be a better way, but here is how I solved my problem:

Dir["app/models/*.rb"].each do |file_path|
  require file_path # Make sure that the model has been loaded.

  basename  = File.basename(file_path, File.extname(file_path))
  clazz     = basename.camelize.constantize

  clazz.find(:all).each do |rec|
    # Important code here...
  end
end

This code assumes that you are following the standard model naming conventions for classes and source code files.

An update for Rails 5.2

For Rails 5.2 you can also use ApplicationRecord to get an Array with your table' names. Just, as imechemi mentioned, be aware that this method will also return ar_internal_metadata and schema_migrations in that array.

ApplicationRecord.connection.tables

Keep in mind that you can remove ar_internal_metadata and schema_migrations from the array by calling:

ApplicationRecord.connection.tables - %w[ar_internal_metadata schema_migrations]