class ActiveRecord::ConnectionAdapters::PostgreSQL::SchemaCreation

def visit_AlterTable(o)
  sql = super
  sql << o.constraint_validations.map { |fk| visit_ValidateConstraint fk }.join(" ")
  sql << o.exclusion_constraint_adds.map { |con| visit_AddExclusionConstraint con }.join(" ")
  sql << o.unique_constraint_adds.map { |con| visit_AddUniqueConstraint con }.join(" ")
end