def add_exclusion_constraint(expression, options)
  @exclusion_constraint_adds << @td.new_exclusion_constraint_definition(expression, options)
end

def add_unique_constraint(column_name, options)
  @unique_constraint_adds << @td.new_unique_constraint_definition(column_name, options)
end

def initialize(td)
  super
  @constraint_validations = []
  @exclusion_constraint_adds = []
  @unique_constraint_adds = []
end

def validate_constraint(name)
  @constraint_validations << name
end