Create a Smart relationship

What is a Smart Relationship?
Sometimes, you want to create a virtual relationship between two set of data that does not exist in your database. A concrete example could be creating a relationship between two collections available in two different databases. Creating a Smart Relationship allows you to customize with code how your collections are linked together.
Create a BelongsTo Smart Relationship
On the Live Demo example, we have an order which belongsTo a customer which belongsTo a delivery address. We’ve created here a BelongsTo Smart Relationship that acts like a shortcut between the order and the delivery address.
A BelongsTo Smart Relationship is created like a Smart Field with the reference option to indicate on which collection the Smart Relationship points to. You will also need to code the logic of the search query.
SQL
Mongodb
Rails
SQL
/forest/orders.js
const { collection } = require('forest-express-sequelize');
const models = require('../models');
​
collection('orders', {
  fields: [{
    field: 'delivery_address',
    type: 'String',
    reference: 'addresses.id',
    get: function (order) {
      return models.addresses
        .findAll({
          include: [{
            model: models.customers,
            where: { id: order.customer_id },
            include: [{
              model: models.orders,
              where: { ref: order.ref }
            }]
          }],
        })
        .then((addresses) => {
          if (addresses) { return addresses[0]; }
        });
    }
  }]
});
Mongodb
/forest/orders.js
const { collection } = require('forest-express-mongoose');
const Address = require('../models/addresses');
​
collection('Order', {
  fields: [{
    field: 'delivery_address',
    type: 'String',
    reference: 'Address._id',
    get: function (order) {
      return Address
        .aggregate([
          {
            $lookup:
            {
              from: 'orders',
              localField: 'customer_id',
              foreignField: 'customer_id',
              as: 'orders_docs'
            }
          }, 
          {
            $match:
            {
              'orders_docs._id': order._id
            }
          }
        ])
        .then((addresses) => {
          if (addresses) { return addresses[0]._id; }
        });
    }
  }]
});
Rails
lib/forest_liana/collections/order.rb
class Forest::Order
  include ForestLiana::Collection
​
  collection :Order
​
  search_delivery_address = lambda do |query, search|
​
    query.joins(customer: :address).or(Order.joins(customer: :address).where("addresses.country ILIKE ?", "%#{search}%"))
​
  end
​
  belongs_to :delivery_address, reference: 'Address.id', search: search_delivery_address do
    object.customer.address
  end
end
Create a HasMany Smart Relationship
On the Live Demo example, we have a product hasMany orders and an order belongsTo customer. We’ve created a Smart Relationship that acts like a shortcut: product hasMany customers.
A HasMany Smart Relationship is created like a Smart Field with the reference option to indicates on which collection the Smart Relationship points to.
SQL
Mongodb
Rails
SQL
/forest/products.js
const { collection } = require('forest-express-sequelize');
​
collection('products', {
  fields: [{
    field: 'buyers',
    type: ['String'],
    reference: 'customers.id'
  }]
});
Mongodb
/forest/products.js
const { collection } = require('forest-express-mongoose');
​
collection('products', {
  fields: [{
    field: 'buyers',
    type: ['String'],
    reference: 'Customer._id'
  }]
});
Rails
lib/forest_liana/collections/product.rb
class Forest::Product
  include ForestLiana::Collection
​
  collection :Product
​
  has_many :buyers, type: ['String'], reference: 'Customer.id'
end
SQL
Mongodb
Rails
SQL
Upon browsing, an API call is triggered when accessing the data of the HasMany relationships in order to fetch them asynchronously. In the following example, the API call is a GET on /products/:product_id/relationships/buyers.
Option 1: using Sequelize ORM
We’ll use the findAll and count methods provided by Sequelize to find and count all customers who bought the current product (buyers).
Then, you should handle pagination in order to avoid performance issue. The API call has a query string available which gives you all the necessary parameters you need to enable pagination.
Finally, you don’t have to serialize the data yourself. The Forest Liana already knows how to serialize your collection (customers in this example). You can access to the serializer through the recordsGetter.serialize function.
/routes/products.js
const express = require('express');
const { PermissionMiddlewareCreator, RecordSerializer } = require('forest-express-sequelize');
const { products, customers, orders} = require('../models');
​
const router = express.Router();
const permissionMiddlewareCreator = new PermissionMiddlewareCreator('products');
​
router.get('/products/:product_id/relationships/buyers', (request, response, next) => {
  const productId = request.params.product_id;
  const limit = parseInt(request.query.page.size, 10) || 20;
  const offset = (parseInt(request.query.page.number, 10) - 1) * limit;
  const include = [{
    model: orders,
    as: 'orders',
    where: { product_id: productId },
  }];
​
  // find the customers for the requested page and page size
  const findAll = customers.findAll({
    include,
    offset,
    limit,
  });
​
  // count all customers for pagination
  const count = customers.count({ include });
​
  // resolve the two promises and serialize the response
  const serializer = new RecordSerializer(customers);
  Promise.all([findAll, count])
    .then(([customersFound, customersCount]) =>
      recordsGetter.serialize(customersFound, { count: customersCount }))
    .then((recordsSerialized) => response.send(recordsSerialized))
    .catch(next);
});
Option2: using raw SQL
We’ll use raw SQL query and Sequelize to count and find all customers who bought the current product (buyers).
Then, you should handle pagination in order to avoid performance issue. The API call has a query string available which gives you all the necessary parameters you need to enable pagination.
Finally, you don’t have to serialize the data yourself. The Forest Liana already knows how to serialize your collection (customers in this example). You can access to the serializer through the recordsGetter.serialize function.
/routes/products.js
const express = require('express');
const router = express.Router();
const models = require('../models');
​
router.get('/products/:product_id/relationships/buyers', (req, res, next) => {
  let limit = parseInt(req.query.page.size) || 10;
  let offset = (parseInt(req.query.page.number) - 1) * limit;
  let queryType = models.sequelize.QueryTypes.SELECT;
​
  let countQuery = `
    SELECT COUNT(*)
    FROM customers
    JOIN orders ON orders.customer_id = customers.id
    JOIN products ON orders.product_id = products.id
    WHERE product_id = ${req.params.product_id};
  `;
​
  let dataQuery = `
    SELECT customers.*
    FROM customers
    JOIN orders ON orders.customer_id = customers.id
    JOIN products ON orders.product_id = products.id
    WHERE product_id = ${req.params.product_id}
    LIMIT ${limit}
    OFFSET ${offset}
  `;
​
  const serializer = new RecordsSerializer(customers);
  return Promise
    .all([
      models.sequelize.query(countQuery, { type: queryType }),
      models.sequelize.query(dataQuery, { type: queryType })
    ])
    .then(([count, customers]) => serializer.serialize(customers, { count: count[0].count }))
    .then((customers) => res.send(customers))
    .catch((err) => next(err));
});
​
module.exports = router;
If your primary key column name (customer_id) is different than the model field name (customerId), you must alias the primary key column with the name of the model field in the dataQuery. 

Ex: SELECT customers.*, customers.customer_id AS “customerId”
Mongodb
Upon browsing, an API call is triggered when accessing the data of the HasMany relationships in order to fetch them asynchronously. In the following example, the API call is a GET on /Product/:product_id/relationships/buyers.
We use the $lookup operator of the aggregate pipeline. Since there's a many-to-many relationship between Product and Customer, the $lookup operator needs to look into orders which is an array we have to flatten first using $unwind.
Finally, you don’t have to serialize the data yourself. The Forest Liana already knows how to serialize your collection (Customer in this example). You can access to the serializer through the Liana.ResourceSerializer object.
/forest/products.js
const { collection } = require('forest-express-mongoose');
​
collection('products', {
  fields: [{
    field: 'buyers',
    type: ['String'],
    reference: 'Customer._id'
  }]
});
/routes/products.js
const P = require('bluebird');
const express = require('express');
const router = express.Router();
const Liana = require('forest-express-mongoose');
const { Customers } = require('../models');
const mongoose = require('mongoose');
​
router.get('/Product/:product_id/relationships/buyers', (req, res, next) => {
    let limit = parseInt(req.query.page.size) || 10;
    let offset = (parseInt(req.query.page.number) - 1) * limit;
​
    let countQuery = Customers.aggregate([
          {
            $lookup:
            {
              from: 'orders',
              localField: 'orders',
              foreignField: '_id',
              as: 'orders_docs'
            }
          },
          {
            $unwind: "$orders_docs"
          },
          {
            $lookup:
            {
              from: 'products',
              localField: 'orders_docs._id',
              foreignField: 'orders',
              as: 'products_docs'
            }
          },
          {
            $match:
            {
              'products_docs._id': mongoose.Types.ObjectId(req.params.product_id)
            }
          },
          {
            $count: "products_docs"
          }
        ]);
​
    let dataQuery = Customers.aggregate([
          {
            $lookup:
            {
              from: 'orders',
              localField: 'orders',
              foreignField: '_id',
              as: 'orders_docs'
            }
          },
          {
            $unwind: "$orders_docs"
          },
          {
            $lookup:
            {
              from: 'products',
              localField: 'orders_docs._id',
              foreignField: 'orders',
              as: 'products_docs'
            }
          },
          {
            $match:
            {
              'products_docs._id': mongoose.Types.ObjectId(req.params.product_id)
            }
          }
        ]);
​
    return P
      .all([
        countQuery,
        dataQuery
      ])
      .spread((count, customers) => {
        const serializer = new Liana.RecordSerializer(Customers);
        return serializer.serialize(customers, { count: count.orders_count });
      })
      .then((products) => {
        res.send(products);
      })
      .catch((err) => next(err));
  });
​
module.exports = router;
Rails
Upon browsing, an API call is triggered when accessing the data of the HasMany relationships in order to fetch them asynchronously. In the following example, the API call is a GET on /Product/:product_id/relationships/buyers.
We’ve built the right SQL query using Active Record to count and find all customers who bought the current product.
Then, you should handle pagination in order to avoid performance issue. The API call has a querystring available which gives you all the necessary parameters you need to enable pagination.
Finally, you don’t have to serialize the data yourself. The Forest Liana already knows how to serialize your collection (Customer in this example). You can access to the serializer through the serialize_models() function.
Rails.application.routes.draw do
  # MUST be declared before the mount ForestLiana::Engine.
  namespace :forest do
    get '/Product/:product_id/relationships/buyers' => 'orders#buyers'
  end
  
  mount ForestLiana::Engine => '/forest'
end

class Forest::ProductsController < ForestLiana::ApplicationController
  def buyers
    limit = params['page']['size'].to_i
    offset = (params['page']['number'].to_i - 1) * limit
​
    orders = Product.find(params['product_id']).orders
    customers = orders.limit(limit).offset(offset).map(&:customer)
    count = orders.count
​
    render json: serialize_models(customers, include: ['address'], meta {count: count})
  end
end
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