title: Sequelize intermediate table relationship
body: <p>I need make the next relation:</p>
  
  <p>I have selection_process and documents, the selection_process can have many documents but the documents can only belong to one selection_process. I cant know how many documents will a selection_process have, so I use a intermediate table, in that table 'documents_selection' i have the id_document and the id_process_selection.</p>
  
  <p>I have already used a many to many relation using a intermediate table here:</p>
  
  <pre><code>ProspectModel.belongsToMany(CategoriesModel, { through: CategoriesProspModel, foreignKey: 'id_prospecto'})
  CategoriesModel.belongsToMany(ProspectModel, { through: CategoriesProspModel, foreignKey: 'id_categoria'})
  </code></pre>
  
  <p>This case is diferent, Prospect can belong to many Categories and Categories can have many Prospect, no problem, but in the other case the Documents can only belong to one process_selection.</p>