title: Composite primary key in Sequelize
body: <p>Can someone suggest how do I set primary key on two columns within the same table.</p>
  <pre><code>var relation = {
          'user_id': {
              type: DataTypes.INTEGER
          },
          'organization_id':{
              type: DataTypes.INTEGER
          }
  }
  </code></pre>
  <p>I want to define a primary key like <code> primary key (user_id, organization_id)</code></p>
  <p>Note: Using <code>PostgreSQL</code></p>