JSDoc: Tutorial: 003 - Select

The selected columns can be limited by using the FromAdapter#select method. It's variadic, and in its simplest form it can be passed an array of fully-qualified column names. A fully-qualified column name takes the form <table-alias>.<column-name>. For example, the bike_shops table is aliased bs in the proceeding example, so limiting the above query to bikeShopID and name is done in the following manner:

'use strict';

const MySQLDriver = require('node-data-mapper-mysql').MySQLDriver;
const driver      = new MySQLDriver(require('../bikeShopConOpts.json'));

driver
  .initialize()
  .then(runQuery)
  .then(printResult)
  .catch(console.error)
  .finally(() => driver.end());

function runQuery(dataContext) {
  const query = dataContext
    // The table is aliased "bs" for convenience.
    .from('bike_shops bs')
    // Select only the ID and name of the shop.
    .select('bs.bikeShopID', 'bs.name');

  // This is the query that will be executed.
  console.log('Query:');
  console.log(query.toString(), '\n');

  // Executing a query returns a promise.
  return query
    .execute();
}

function printResult(result) {
  console.log('Result:');
  console.log(result);
}

It's worth mentioning that when limiting columns, the primary key is required to be one of the selected columns. If columns are selected from a table and the primary key is not one of the columns, then an exception will be raised.

This example prints the following output ($ node example/retrieve/limitColumns.js):

Query:
SELECT  `bs`.`bikeShopID` AS `bs.bikeShopID`,
        `bs`.`name` AS `bs.name`
FROM    `bike_shops` AS `bs` 

Result:
{ bike_shops: 
   [ { bikeShopID: 1, name: 'Bob\'s Bikes' },
     { bikeShopID: 2, name: 'Zephyr Cove Cruisers' },
     { bikeShopID: 3, name: 'Cycle Works' } ] }

Tutorial: 003 - Select - Limiting Columns

003 - Select - Limiting Columns