title: Sequelize query to get records not in associations
body: <p>There are two tables userMedium and medium. medium hasMany userMedia. For a user, wanna get the medium records that not included in the userMedia. With the Sequelize library, it was implemented as:</p>
  
  <pre><code>const um = await Models.UserMedium.findAll({
      where: {userId},
      attributes: ['mediumId']
    }),
       media = await Models.Medium.findAll({
            where: {
              id: {
                $notIn: _.pluck(um, 'mediumId')
              }
            }
          });
  </code></pre>
  
  <p>Wonder is there a better way to run the query by using the eager loading?</p>