Merge pull request #2471 from benjaminwil/addresses_documentation

Addresses documentation

Author: jhawthorn

guides/users/addresses.md

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+# Addresses
+
+The `Spree::Address` model is used to track address information for customers.
+Addresses are consumed by `Spree::Order`s, `Spree::Shipment`s, and
+`Spree::Carton`s.
+
+If your store uses the [`solidus_auth_devise`][solidus-auth-devise] gem,
+customers belong to the `Spree::User` model. A customer may have multiple
+addresses. For example, it is typical for customers to have separate billing and
+shipping addresses.
+
+You may want to find all of the addresses associated with a `Spree::User`:
+
+```ruby
+Spree::User.find(1).addresses
+```
+
+`Spree::Address` objects have the following attributes:
+
+- `firstname`: The first name for the person at this address.
+- `lastname`: The last name for the person at this address.
+- `address1` and `address2`: The street address (with an optional second line).
+- `city`: The city where the address is.
+- `zipcode`: The postal code.
+- `phone` and `alternative_phone`: The customer's phone number(s).
+- `state_name`: If the customer uses a region name that doesn't correspond with
+  a country's list of states, the address can store the user-entered
+- `state_name` as a fallback. 
+- `alternative_phone`: The alternative phone number.
+- `company`: A company name.
+- `state_id` and `country_id`: IDs for the `Spree::State` and `Spree::Country`
+  objects associated with the customer's entered address. These are used to
+  determine the customer's [zone][zones], which determines applicable taxation
+  and shipping methods.
+
+For more information about how countries, states, and zones work in Solidus, see
+the [Locations][locations] documentation.
+
+[locations]: ../locations/index.md
+[solidus-auth-devise]: https://github.com/solidusio/solidus_auth_devise
+[zones]: ../locations/zones.md
+
+## Countries and states 
+
+Countries and states can affect both taxation and shipping on orders. So, an
+address must always link to a `Spree::Country` object. Because some countries do
+not have associated `Spree::State`s, a state object is not required.
+
+If the user-entered state does not correspond with a `Spree::Country`'s
+associated states, then the `state_name` attribute is used to record the state
+name.
+
+If you use the `solidus_frontend` gem to provide your store's frontend, the
+state field is hidden if the customer's country does not have `Spree::State`s
+associated with it.
+
+## Required address values
+
+By default, `Spree::Address` objects require many address values, including a
+phone number and zip code value.
+
+You may want to alter Solidus's address requirements for your store. For
+example, if you do not require customer phone numbers in order for them to check
+out.
+
+Right now, you need to [monkey-patch][monkey-patch] the `Spree::Address` model
+in order to change its requirements. For example, you could prepend your custom
+behavior that redefines `Spree::Address`'s `require_phone?` method: 
+
+```ruby
+module PhoneNotRequired
+  def require_phone?
+    false
+  end
+end
+
+Spree::Address.prepend(PhoneNotRequired)
+```
+
+Similarly, if you ship to countries that don't require postal codes, like Hong
+Kong or Macau, you may want to make postal codes optional instead of required.
+
+Right now, you can monkey-patch the `Spree::Address` model in order to remove or
+change the requirements. For example, you could prepend your own custom behavior
+that redefines `Spree::Address`'s `require_zipcode?` method:
+
+```ruby
+module ZipCodeValidation
+  def require_zipcode?
+    # if a country that you ship to does not require postal codes, add its iso
+    # code to the following array so that Spree::Address does not require zip
+    # codes for addresses in those countries.
+    !['HK','MO'].include?(country.iso)
+  end
+end
+
+Spree::Address.prepend(ZipCodeValidation)
+```
+
+<!-- TODO:
+  Ideally, we do not want to recommend monkey-patching the Spree::Address model.
+  It would be great make address requirements more configurable in general.
+  Then, we can revisit this documentation.
+-->
+
+[monkey-patch]: https://en.wikipedia.org/wiki/Monkey_patch