# Shipping method filters

While shipping method filters occur automatically, your store may require additional shipping method filtering.

# Default behavior

Shipping methods are automatically filtered by zone. This means that once the customer provides a shipping address during checkout, the shipping methods that the customer can choose from are limited to the shipping methods available in their region.

For example, if your store does not have a zone that includes the United Kingdom, then a customer cannot complete the checkout process if their shipping address is within the United Kingdom.

# Shipping method availability

The base Spree::Calculator's available? method returns true by default.

You can see the shipping_methods being filtered out in the Spree::Stock::Estimator class below:

class Spree::Stock::Estimator
  def shipping_methods(package)
    shipping_methods = package.shipping_methods
    shipping_methods.delete_if { |ship_method| !ship_method.calculator.available?(package.contents)  }
    shipping_methods.delete_if { |ship_method| !ship_method.include?(order.ship_address)  }
    shipping_methods.delete_if { |ship_method| !(ship_method.calculator.preferences[:currency].nil? || ship_method.calculator.preferences[:currency] == currency)  }
    shipping_methods
  end
end

# Add additional criteria to filter by

Consider a custom "USPS Bogus First Class International" delivery service. This service is only available if the shipment weighs less than 10lbs.

We want to ensure that "USPS Bogus First Class International" shipping is not available when orders weigh more than 10lbs. So, we want to set our shipping calculator's available? method to false if the collective weight of an order's line items are greater than 10lbs:

class Calculator::Usps::FirstClassMailParcels < Calculator::Usps::Base
  def self.description
    "USPS Bogus First Class International"
  end

  def available?(package)
    multiplier = 1.3
    weight = order.line_items.inject(0) do |weight, line_item|
      weight + (line_item.variant.weight ? (line_item.quantity * line_item.variant.weight * multiplier) : 0)
    end
    # If weight in oz  > 13, then "USPS Bogus First Class International" is not available for the order
    weight > 13 ? false : true
  end
end