createLoader.js

const DataLoader = require('dataloader')

/**
 * Creates a dataloader for a supplied model.
 * 
 * @param {String} model e.g. 'App/Models/User'
 * @param {String} ref_id e.g. 'order_id'
 * @returns {DataLoader}
 */
function createLoader(model, ref_id = 'id', has = 'one') {
  let batchLoadFn = async (keys) => {
    let data = await queryData(model, ref_id, keys)

    return sortData(data.rows, ref_id, keys, has)
  }
  return new DataLoader(batchLoadFn)
}

// 這裡是adonis.js的query範例.
// 可以將queryData的內容抽換成你query db的方式。
async function queryData(model, ref_id, keys) {
  let Model = use(model)
  console.log(`*** loading all '${model}' with ids [${keys}] from database`)
  return await Model
    .query()
    .whereIn(ref_id, keys)
    .fetch()
}

function sortData(data, ref_id, keys, has) {
  if (has === 'one') {
    return keys.map(id => data.find(r => r[ref_id] === id))
  } else {
    return keys.map(id => data.filter(r => r[ref_id] === id))
  }
}


module.exports = createLoader