CategoryController.js

import db from './../models';
const categoryController = {};

categoryController._cacheById = {};
categoryController._arrayCache = [];

categoryController.init = () =>{
    return db.Category
        .find({'isDeleted':false})
        .then((categories) => {
            categories.forEach((category) => {
                category = category.toJSON();
                categoryController._cacheById[category._id] = category;

            });
            categoryController._arrayCache = categories;
        })
};

categoryController.getCategoryById = (id) =>{
    console.log(categoryController._cacheById[id]);
    return categoryController._cacheById[id];
};

ImageController.js

import categoryController from './categoryController';

const imageController = {};

imageController._cacheById = {};
imageController._cache = {};

imageController.init = () =>{
    return db.Image
        .find({'isDeleted':false})
        .then( images =>{
            images.forEach( image =>{
                image = image.toJSON();
                image.categories = image.categories.map( id =>{
                    return categoryController.getCategoryById(id);
                })
            });
            imageController._cache = images;
        })

};

imageController.getAllImages = (req,res)=>{
    res.json(imageController._cache);
};