01-mapping-between-models-and-database-tables

Mapping between models and database tables

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By default, Active Record uses some naming conventions to find out how the mapping between models and database tables should be created.

Model	Table	Foreign key
Pokemon	pokemons	pokemon_id
Move	moves	move_id
PokemonMove	pokemon_moves	pokemon_move_id

See Naming conventions for more details.

It allows you to write:

class Pokemon < ActiveRecord::Base
  has_many :pokemon_moves
  has_many :moves, through: :pokemon_moves
end

instead of:

class Pokemon < ActiveRecord::Base
  self.table_name = 'pokemons'
  has_many :pokemon_moves, class_name: 'PokemonMove', foreign_key: 'pokemon_id'
  has_many :moves, through: :pokemon_moves, source: :move
end

By that, you should understand pokemon.moves as pokemon.pokemon_moves.map(&:move) and pokemon.pokemon_moves as PokemonMove.where('pokemon_id = ?', pokemon.id).

In order to do that, we will need the following methods:

• pluralize
• singularize
• camelize
• underscore
• demodulize
• tableize
• classify
• constantize
• foreign_key

See Inflections for a complete reference.

Challenge

Implement the ActiveRecord::Support::Inflector class, run specs and play with the REPL.

Specs

make test

Playground

make play

Quick start

Open lib/active-record/support/inflector.rb, spec/active-record/support/inflector_spec.rb and spec/data/inflections.json.