Question

I have a rake task that won’t work unless a table exists. I’m working with more than 20 engineers on a website so I want to make sure they have migrated the table before they can do a rake task which will populate that respective table.

Does AR have a method such as Table.exists? How can I make sure they have migrated the table successfully?

Answer 1

In Rails 5 the API became explicit regarding tables/views, collectively data sources.

# Tables and views
ActiveRecord::Base.connection.data_sources
ActiveRecord::Base.connection.data_source_exists? 'kittens'

# Tables
ActiveRecord::Base.connection.tables
ActiveRecord::Base.connection.table_exists? 'kittens'

# Views
ActiveRecord::Base.connection.views
ActiveRecord::Base.connection.view_exists? 'kittens'

In Rails 2, 3 & 4 the API is about tables.

# Listing of all tables and views
ActiveRecord::Base.connection.tables

# Checks for existence of kittens table/view (Kitten model)
ActiveRecord::Base.connection.table_exists? 'kittens'

Getting the status of migrations:

# Tells you all migrations run
ActiveRecord::Migrator.get_all_versions

# Tells you the current schema version
ActiveRecord::Migrator.current_version

If you need more APIs for migrations or metadata see:

• ActiveRecord::SchemaMigration
  this is the ActiveRecord::Base class for the schema_migrations table
• ActiveRecord::Migrator
  where all the action happens when migrations are run