Data Access Object and Lazy Loading Pattern

Data Access Object (DAO) is an object containing methods that retrieve data from a database or trigger database queries. Together with the idea of Lazy Loading, we could set up a pattern as follows.

Imagine we have a schema with a table 'books' with fields id, title and year, and a separate table for 'authors'.

// High level books object to access a 'books' table
const Books = {
  getBooks() {
    // Database query to retrieve all books
    const result // = Database query here

    // Assume that result is a 2D array
    // Map each query result into a Book object
    const books = result.map((book) => new Book(book[0], book[1], book[2]))
  }
}


// Book class that can be instantiated to represent each book
class Book {
  constructor(id, title,  year) {
    this.id = id;
    this.title = title;
    this.year = year;
  }

  getAuthor() {
    // Database query to retrieve author
    const author // = Database query to retrieve related author with book id
    return author
  }
}

Notes:

To reduce overhead, retrieving all books will only retrieve high level data without getting all relational data.
Each Book instance has access to relational data (Author) and can be called as needed.

Data Access Object and Lazy Loading Pattern ​

Data Access Object and Lazy Loading Pattern