title: Sequelize one-to-many query (with include) produces Y is not associated to X
body: <p>so i'm having problems with sequelize's one to many relationship, my associations are defined like this:</p>
  
  <pre><code>X.hasMany(Y, { as: 'Ys' });
  Y.belongsTo(X, { as: 'X' });
  </code></pre>
  
  <p>and my findAll is here:</p>
  
  <pre><code>return X.findAll(
          {
              where: {
                  something: something,
              },
              include: [{ model: db.Y, as: 'Ys' }]
          }
      );
  </code></pre>
  
  <p>and this is producing the error:</p>
  
  <blockquote>
    <p>"error": "Y (Ys) is not associated to X!"</p>
  </blockquote>
  
  <p>Not quite sure what i'm doing wrong here :/</p>