Adjust feathersjs with sequelize to allow models to set up relationships

all-of-your-models.js

// Only showing relevant changes
// The folllowing changes must be made in all of your models

var Author = sequelize.define('Authors', {
  ...
}, {
  classMethods: {
    // Create a static 'associate' method - will be called later
    associate: function (models) {
      Author.hasMany(models.Books, { as: 'books' });
    }
  }
});

// Syncing is done elsewhere - don't do it here
// Author.sync();

all-of-your-services.js

// Only showing relevant changes
// The following changes must be made in all of your services

// No need to import your model any more
// const Author = require('./author');

module.exports = function(){
  const app = this;
  // reference your model this way
  const models = app.get('models');

  const options = {
    Model: models.Authors,
    ...
  }
};

services-index.js

// Only showing relevent changes
const path = require('path');

module.exports = function() {
  ...
  app.set('sequelize', sequelize);
  app.set('models', associateModels(sequelize));
  sequelize.sync();
  ...
};

function associateModels (sequelize) {
  var models = {};
  ['author', 'book'].forEach(function(modelName) {
    var model = sequelize.import(path.join(__dirname, './' + modelName + '/' + modelName + '-model'));
    models[model.name] = model;
  });
  Object.keys(models).forEach(function(modelName) {
    if ("associate" in models[modelName]) {
      models[modelName].associate(models);
    }
  });
  return models;
}