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    <p><a href="http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html" rel="nofollow noreferrer">The documentation for ActiveRecord associations has a section on <code>has_one</code> vs <code>belongs_to</code>.</a> In addition, the <a href="http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html#M001834" rel="nofollow noreferrer">section on <code>has_one</code></a> mentions that this should be used only if the <em>other class</em> has the foreign key. So, to model what you want, you would use.</p> <pre><code>class Address &lt; ActiveRecord::Base has_one :shipto_customer, :class_name =&gt; "Customer", :foreign_key =&gt; "shipping_address_id" has_one :billto_customer, :class_name =&gt; "Customer", :foreign_key =&gt; "billing_address_id" end class Customer &lt; ActiveRecord::Base belongs_to :shipping_address, :class_name =&gt; "Address" belongs_to :billing_address, :class_name =&gt; "Address" end </code></pre> <p>Example usage:</p> <pre><code>&gt;&gt; customer = Customer.new(:name =&gt; "John Smith", ?&gt; :shipping_address =&gt; Address.new(:address =&gt; "123 M St", ?&gt; :city =&gt; "Phoenix", :state =&gt; "AZ", :zip =&gt; "85015"), ?&gt; :billing_address =&gt; Address.new(:address =&gt; "555 W Main Dr", ?&gt; :city =&gt; "Phoenix", :state =&gt; "AZ", :zip =&gt; "85015") &gt;&gt; ) =&gt; #&lt;Customer id: nil, name: "John Smith", billing_address_id: nil, shipping_address_id: nil, created_at: nil, updated_at: nil&gt; &gt;&gt; customer.save Address Create (0.8ms) INSERT INTO "addresses" ("address", "city", "zip", "created_at", "updated_at", "state") VALUES('555 W Main Dr', 'Phoenix', '85015', '2009-11-14 17:03:28', '2009-11-14 17:03:28', 'AZ') Address Create (0.2ms) INSERT INTO "addresses" ("address", "city", "zip", "created_at", "updated_at", "state") VALUES('123 M St', 'Phoenix', '85015', '2009-11-14 17:03:28', '2009-11-14 17:03:28', 'AZ') Customer Create (0.2ms) INSERT INTO "customers" ("name", "billing_address_id", "shipping_address_id", "created_at", "updated_at") VALUES('John Smith', 1, 2, '2009-11-14 17:03:28', '2009-11-14 17:03:28') =&gt; true &gt;&gt; customer.shipping_address =&gt; #&lt;Address id: 2, address: "123 M St", city: "Phoenix", state: "AZ", zip: "85015", created_at: "2009-11-14 17:03:28", updated_at: "2009-11-14 17:03:28"&gt; &gt;&gt; customer.billing_address =&gt; #&lt;Address id: 1, address: "555 W Main Dr", city: "Phoenix", state: "AZ", zip: "85015", created_at: "2009-11-14 17:03:28", updated_at: "2009-11-14 17:03:28"&gt; &gt;&gt; </code></pre>
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    1. POCan this relationship be described in Ruby on Rails?
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    1. USMatt Haley
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    1. COThe OP wanted to be able to share addresses between customers, so the relationships in the `Address` model should be `has_many` rather than `has_one` relationships.
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      1. USPär Wieslander
    2. COIt doesn't seem quite clear from the OP's post, in the data example he's showing addresses being shared, ie: has_many, in the code example he's suggesting has_one. Then he states that he'd rather not have many-to-many. In my opinion, shared addresses would be a bad idea. What happens when customer A updates his current address to add a zip+4, or an Apt number?
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      1. USMatt Haley
    3. COYes, shared addresses are definitely troublesome. Keeping addresses and customers in separate tables is probably a good idea for clarity, but sharing references to address rows will most likely cause problems when deciding how to handle address updates.
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      1. USPär Wieslander
 

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