Knex - caching

SQLCache.js

const { InMemoryLRUCache } = require("apollo-server-caching");

class SQLCache {
  constructor(cache = new InMemoryLRUCache()) {
    this.cache = cache;
  }

  async knexPlugin(knexThen, ctx, args) {
    const isSelectStatement = ctx._method === "select";

    if (isSelectStatement) {
      // Make a cacheKey that is sure to be unique
      const normalizedQuery = ctx.toQuery().replace(/["']/g, "").toLowerCase();
      const cacheKey = `sqlcache:${normalizedQuery}`;
      // Serious shenanigans to support Knex not having plugins
      // if you do not manually call the .then() after saving to cache
      // then the code-level .then()s will fire _first_ and leave you with
      // a potentially fifferent result and then you cache the wrong thing
      // :sadpanda:
      const hasPromiseFn = Boolean(
        args && args[0] && typeof args[0] === "function"
      );
      const promiseChain = hasPromiseFn ? args[0] : value => value;
      const entry = await this.cache.get(cacheKey);
      if (entry) {
        // If there is a cache hit, return it without hitting the DB
        return Promise.resolve(entry).then(promiseChain);
      } else {
        // If there is not a hit, query the DB and cache the result
        return knexThen
          .apply(ctx)
          .then(result => {
            this.cache.set(cacheKey, result);
            return Promise.resolve(result);
          })
          .then(promiseChain);
      }
    } else {
      return knexThen.apply(ctx, args);
    }
  }
}

module.exports = SQLCache;

SQLDataSource.js

const KnexQueryBuilder = require("knex/lib/query/builder");
const SQLCache = require("./SQLCache");

class SQLDataSource {
  initialize(config) {
    this.context = config.context;
    const dbCache = new SQLCache(config.cache);

    // This is an ugly hack to compensate for Knex not having plugins yet
    const knexThen = KnexQueryBuilder.prototype.then;
    KnexQueryBuilder.prototype.then = function() {
      return dbCache.knexPlugin(knexThen, this, arguments);
    };
    this.knex.queryBuilder = () => new KnexQueryBuilder(this.knex.client);

    this.db = this.knex;
  }
}

module.exports = SQLDataSource;

ThingsDB.js

const Knex = require("knex");
const SQLDataSource = require("../utils/SQLDataSource");

const { PG_HOST, PG_DATABASE, PG_USER, PG_PASSWORD, PG_PORT } = process.env;

class ThingsDB extends SQLDataSource {
  constructor() {
    super();

    // Add an instance of Knex for the base class to use
    this.knex = Knex({
      client: "pg",
      connection: {
        host: PG_HOST,
        user: PG_USER,
        password: PG_PASSWORD,
        database: PG_DATABASE,
        port: PG_PORT
      }
    });
  }

  getThing({ id }) {
    return this.db
      .select()
      .from("things")
      .where({ id });
  }
}

module.exports = ThingsDB;