method

sole

rails latest stable - Class: Enumerable
sole()
public

Returns the sole item in the enumerable. If there are no items, or more than one item, raises +Enumerable::SoleItemExpectedError+.

["x"].sole          # => "x"
Set.new.sole        # => Enumerable::SoleItemExpectedError: no item found
{ a: 1, b: 2 }.sole # => Enumerable::SoleItemExpectedError: multiple items found