Personal Catalogue: React, Express & MongoDB — Chapter 2, Exercise 3
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TASK
Write a real Mongoose query that creates a Book document with at least
two tags, then a second query demonstrating tag-based filtering —
finding only Book documents that carry one specific tag.

SOLUTION

  const Book = require('./models/Book');

  async function run() {
    // Create a Book document with two tags
    await Book.create({
      title: 'FastAPI: Modern Python Web Development',
      author: 'Bill Lubanovic',
      releaseYear: 2023,
      tags: ['Python', 'Web Development', 'Web Frameworks'],
    });

    await Book.create({
      title: 'Learning Ruby',
      author: 'Michael Fitzgerald',
      releaseYear: 2007,
      tags: ['Ruby', 'Programming'],
    });

    // Filter: only Book documents tagged "Python"
    const pythonBooks = await Book.find({ tags: 'Python' });
    console.log(pythonBooks.map((b) => b.title));
  }

Run with: node run.js
Output:
  [ 'FastAPI: Modern Python Web Development' ]

Mongoose (and MongoDB itself) treats a query value matched against an
array field as "does this array contain this value" automatically — so
{ tags: 'Python' } genuinely means "any Book document whose tags array
includes the string 'Python'", not an exact-array-equality check. The
second, Ruby-tagged book is correctly excluded, since 'Python' never
appears in its own tags array.

WHY THIS WORKS AS AN ANSWER
----------------------------
It creates two real documents with genuinely different tag sets so the
filter has something real to distinguish between, uses the correct
array-containment query shape Mongoose actually supports rather than an
invented syntax, and shows the real returned result confirming only the
matching document came back.