Specify inverse_of on associations

[scottohara]

rubocop@0.52 introduced a new Rails/InverseOf cop (enabled by default).

The cop requires all has_one/has_many <=> belongs_to associations where Rails can't automatically determine the inverse relationship (such as in the presence of a class_name: or foreign_key: attribute) to explicitly specify the inverse relationship using inverse_of:.

This caused a number of offences, and when trying to add the missing inverse_of: attributes, a number of problems were encountered (below), so this cop has been locally disabled for now.

If we can resolve these issues, the cop can be reenabled (preferred).

Issues:

• Account model defines an optional self-referential related_account association as follows:

  belongs_to :related_account, class_name: 'Account', foreign_key: 'related_account_id', autosave: true, optional: true

There is no inverse has_one association defined, so it is currently unclear if there should be one.

• Category model has a parent/child association as follows:

  belongs_to :parent, class_name: 'Category', foreign_key: 'parent_id', optional: true
  has_many :children, -> { order :name }, class_name: 'Category', foreign_key: 'parent_id', dependent: :destroy

Adding inverse_of: :children and inverse_of: :parent (respectively) caused a Stack level too deep error when trying to run the test suite.

• TransactionCategory model has an association back to the base Transaction model as follows:

  belongs_to :trx, foreign_key: 'transaction_id', class_name: 'Transaction'

But as only some transaction types are categorisable (e.g. BasicTransaction, Subtransaction), adding inverse_of: :transaction_category can't work as there's no Transaction.transaction_category association.

This may require using polymorphic: true and as:, e.g.

# basic_transaction.rb
has_one :transaction_category, foreign_key: 'transaction_id', dependent: :destroy, as: :categorisable_transaction

# transaction_category.rb 
belongs_to :categorisable_transaction, foreign_key: 'transaction_id', class_name: 'Transaction', polymorphic: true