jerni

a framework to build data-driven products from the ground up

// Declaratively read data from a collection during projection stage
const readPipeline = require("@jerni/store-mongo/readPipeline");
/* transform function for Profiles model */        
function transform(event) {
  const results = readPipeline([
    { $match: { age: { $gte: 18 } } },
    { $count: 'adultsCount' },
  ]);
  
  // if $match doesn't find any document, next stage will receive empty stream,
  // thus $count stage will just return empty stream as well
  const count = result.length === 0 ? 0 : result[0].adultsCount;
  // decide what to do depending on the value of count
  if (count > 3) {
    return [ /* ... */ ];
  }
  return [ /* ... */ ];
}

// Declaratively read data from a collection during projection stage
const readPipeline = require("@jerni/store-mongo/readPipeline");
const ProductModel = new Model(/* ... */);
const OrderModel = new Model({
  name: "orders",
  version: "1",
  transform(event) {
    // readPipeline can run conditionally
    if (event.type === "ORDER_MADE") {
      const { product_ids, order_id } = event.payload;
      // readPipeline can run repetatively in a loop
      const unitPrices = product_ids.map(id => {
        // readPipeline can run agaist other models as well
        return readPipeline(ProductModel, [
          { $match: { id } },            // query a specific product
          { $project: { unitPrice: 1 } } // only get its price
        ])
      });
      // NOTE: don't do this in production, use one pipeline to map/reduce for better performance
      const total = unitPrices.reduce((a, b) => a + b);
      return [{
        insertOne: {
          id: order_id,
          products: product_ids,
          total
        }
      }]
    }
  }
})
/* transform function for Profiles model */        
function transform(event) {
  const results = readPipeline([
    { $match: { age: { $gte: 18 } } },
    { $count: 'adultsCount' },
  ]);
  
  // if $match doesn't find any document, next stage will receive empty stream,
  // thus $count stage will just return empty stream as well
  const count = result.length === 0 ? 0 : result[0].adultsCount;
  // decide what to do depending on the value of count
  if (count > 3) {
    return [ /* ... */ ];
  }
  return [ /* ... */ ];
}