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POActiveRecord and use of has_one & has_many
 

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    <p>Consider this simple model, where a <code>Project</code> has one <code>ProjectType</code> and, naturally many <code>Projects</code> can be of that type.</p> <p>So a <code>Project</code> <code>has_one :project_type</code> (called <code>type</code>) and a <code>ProjectType</code> <code>has_many :projects</code>.</p> <p>In my migration I put (simplified for this example)</p> <pre><code>create_table :projects do |t| t.string :name, :null =&gt; false t.integer :type end create_table :project_types do |t| t.string :name, :null =&gt; false end </code></pre> <p>My Project class looks like this (again simplified for this example)</p> <pre><code>#!usr/bin/ruby require 'active_record' class Project &lt; ActiveRecord::Base has_one :type, :class_name =&gt; 'ProjectType' end </code></pre> <p>And my ProjectType looks like</p> <pre><code>#!usr/bin/ruby require 'active_record' class ProjectType &lt; ActiveRecord::Base has_many :projects end </code></pre> <p>I've written a simple Unit Test to check this works</p> <pre><code>#test creation of Projects and related objects. def test_projects_and_etc pt = ProjectType.create(:name =&gt; 'Test PT') project = Project.create(:name =&gt; 'Test Project', :type =&gt; pt) assert project.type.name == 'Test PT', "Wrong Project Type Name, expected 'Test PT' but got '#{project.type.name}'." # clean up project.destroy pt.destroy end </code></pre> <p>This test throws an error at the assert, saying</p> <pre><code>ActiveRecord::StatementInvalid: SQLite3::SQLException: no such column: project_types.project_id: SELECT "project_types".* FROM "project_types" WHERE ("project_types".project_id = 1) LIMIT 1 </code></pre> <p>The SQL seems to be assuming that there is a <code>project_id</code> field in the <code>project_types</code> table but that makes no sense if a <code>ProjectType</code> can be associated with many <code>Projects</code>. I suspect that my problem is something to do with my wanting to be able to refer to the <code>ProjectType</code> as <code>project.type</code> not <code>project.project_type</code>, but I am not sure how I'd fix this.</p>
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