declarativ_dry_anti_pattern.rb

# Bad, because declarative code without business logic should NOT be absolutely DRY.

%w[Bob Alice].each do |first_name|
  %w[Black White].each do |second_name|
    Person.create(first_name: first_name, second_name: second_name)
  end
end

# Good, because it's clear, what results the code produces. Declarative, baby!
# Not perfect, because the naming of the params is 
# "kind of business logic" in some situations.

Person.create first_name: 'Bob',   second_name: 'Black'
Person.create first_name: 'Alice', second_name: 'Black'
Person.create first_name: 'Bob',   second_name: 'White'
Person.create first_name: 'Alice', second_name: 'White'

# Better, but a matter of taste.

def create_person(first_name, second_name)
  Person.create first_name: first_name, second_name: second_name
end

create_person 'Bob', 'Black'
create_person 'Alice', 'Black'
create_person 'Bob', 'White'
create_person 'Alice', 'White'

# Bad. The code is not declarative anymore, because it contains business logic.
# Often one can recognize the business logic by it's non-linear control flow.
# Business logic must be DRY.

unless Person.exists?(first_name: 'Bob', second_name: 'Black')
  Person.create(first_name: 'Bob',   second_name: 'Black')
end

unless Person.exists?(first_name: 'Alice', second_name: 'Black')
  Person.create(first_name: 'Alice',   second_name: 'Black')
end

unless Person.exists?(first_name: 'Bob', second_name: 'White')
  Person.create(first_name: 'Bob',   second_name: 'White')
end

unless Person.exists?(first_name: 'Alice', second_name: 'White')
  Person.create(first_name: 'Alice',   second_name: 'White')
end

# Good, because the non-declarative logic (business logic) 
# has been extracted into a DSL method, which now can be used declaratively.

def create_person_unless_exists(first_name, second_name)
  attributes = {first_name: first_name, second_name: second_name}
  Person.create(attributes) unless Person.exists?(attributes)
end

create_person_unless_exists 'Bob', 'Black'
create_person_unless_exists 'Alice', 'Black'
create_person_unless_exists 'Bob', 'White'
create_person_unless_exists 'Alice', 'White'