title: How to put a raw query in sequilize model in one non mapped field
body: <p>I have this in my sportcenter's model:</p>
  <pre><code>import Sequelize from 'sequelize';
  
  export default (sequelize, DataTypes) =&gt; {
      const Sportcenter = sequelize.define('Sportcenter', {
          id: {
              autoIncrement: true,
              type: DataTypes.INTEGER.UNSIGNED,
              allowNull: false,
              primaryKey: true,
          },
          name: {
              type: DataTypes.STRING(500),
              allowNull: true,
          },
          counter: {
              type: DataTypes.VIRTUAL,
          },
         ...
  </code></pre>
  <p>The fields id and name are in database table, but counter is not. I want to relate &quot;counter&quot; with the raw query (e.a. &quot;select count(id) from sportcenter&quot;) and then see it in the json output in the api:</p>
  <pre><code>{
      &quot;id&quot;: 1,
      &quot;name&quot;: &quot;Jose&quot;,
      &quot;counter&quot;: 26,
  },
  {
      &quot;id&quot;: 2,
      &quot;name&quot;: &quot;Pedro&quot;,
      &quot;counter&quot;: 26,
  },
  ...
  </code></pre>
  <p>how can i get that?</p>