title: Query based on included data in Sequelize
body: <p>I have a table for people with a self-association so people can have parents/children/cousins/etc.</p>
  
  <pre><code>const People = sequelize.define('People', {
    gender: Sequelize.STRING,
    name: Sequelize.STRING,
    age: Sequelize.INTEGER
  })
  
  const Relationships = sequelize.define('Relationships')
  Items.belongsToMany(Items, { through: Relationships, as: 'relationships' })
  </code></pre>
  
  <p>I want to be able to select the data in two ways:</p>
  
  <p>1.
  Select all of the relations of a person who are the age of 21</p>
  
  <pre><code>// Returns all of johns relatives who are 21
  return People.findOne({
    where: { name: 'John' },
    include: [{
      required: false,
      model: Items,
      as: 'relationships',
      where: { age: 21 }
    }]
  })
  </code></pre>
  
  <p>2.
  Select all of the people who have a relation who is the age of 21. This will need to accept multiple queries like: Select all of the people who have a relative who is 21 or/and a Male.</p>
  
  <p>Any ideas?</p>