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    <p>Assume you are using Rails 3.</p> <p>You should use <code>habtm</code> when your join table has only 2 foreign keys. For most cases, <code>has_many :through</code> will be more flexible.</p> <p>In your case, you should create a model for the join table. First, you should disable pluralization for legacy DB schema. (I thought you already did that). </p> <pre><code># In config/application.rb config.active_record.pluralize_table_names = false </code></pre> <p>Create a join table, namely <code>CustomerPhoneAddress</code> by convention (I will give it a more meaningful name):</p> <pre><code># customer_phone_address.rb class CustomerPhoneAddress &lt; ActiveRecord::Base belongs_to :address_master belongs_to :customer_master belongs_to :phone_master end </code></pre> <p>Finally, associate your models with <code>has_many</code> and <code>has_many :through</code>:</p> <pre><code># address_master.rb class AddressMaster &lt; ActiveRecord::Base has_many :customer_phone_addresses has_many :customer_masters, :through =&gt; :customer_phone_addresses has_many :phone_masters, :through =&gt; :customer_phone_addresses end # customer_master.rb class CustomerMaster &lt; ActiveRecord::Base has_many :customer_phone_addresses has_many :address_masters, :through =&gt; :customer_phone_addresses has_many :phone_masters, :through =&gt; :customer_phone_addresses end # phone_master.rb class PhoneMaster &lt; ActiveRecord::Base has_many :customer_phone_addresses has_many :customer_masters, :through =&gt; :customer_phone_addresses has_many :phone_masters, :through =&gt; :customer_phone_addresses end </code></pre> <p>I tested the code and it works very well. To create an association:</p> <pre><code>CustomerPhoneAddress.create( :phone_master =&gt; PhoneMaster.first, :address_master =&gt; AddressMaster.first, :customer_master =&gt; CustomerMaster.first) </code></pre> <p>To query the association:</p> <pre><code>IRB&gt; a = AddressMaster.first =&gt; #&lt;AddressMaster id: 1, created_at: "2011-12-07 15:23:07", updated_at: "2011-12-07 15:23:07"&gt; IRB&gt; a.customer_masters =&gt; [#&lt;CustomerMaster id: 1, created_at: "2011-12-07 15:23:15", updated_at: "2011-12-07 15:23:15"&gt;] IRB&gt; a.phone_masters =&gt; [#&lt;PhoneMaster id: 1, created_at: "2011-12-07 15:23:19", updated_at: "2011-12-07 15:23:19"&gt;] IRB&gt; a.customer_phone_addresses =&gt; [#&lt;CustomerPhoneAddress id: 1, address_master_id: 1, customer_master_id: 1, phone_master_id: 1, created_at: "2011-12-07 15:24:01", updated_at: "2011-12-07 15:24:01"&gt;] </code></pre>
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    1. POCustom db entry for 3 way habtm in ROR
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    1. COwith this approach is it okay to create a new instance of a model using the following code? `@customer_master = CustomerMaster.new @customer_master.phone_master.build @customer_master.address_master.build` If i use the above code, I still get 2 db entries in CustomerPhoneAddress
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    2. COalso is it a problem if the customer_phone_address join table has an id? I read in the documentation that the join table shouldn't have an id ..
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    3. COI suggest not to create the association with `build`. As you tried, it will automatically create a row in the join table with only the two foreign key filled.
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