Mongo II Lab: StackQuery

Topics:

• Advanced nested schema
• Schema types (Number, String, Boolean, ObjectId, Date, Buffer, Array)
• Validation via mongoose
• Relationships in MongoDB
• Advanced Queries
  • Field equals
  • Multiple conditions
  • $or conditions
  • Array contains
  • $in conditions

Description

This lab, StackQuery, is all about advanced queries. You'll be populating MongoDB with JavaScript questions and answers from StackOverflow. Then you'll query that dataset in various ways. In some sense, each query represents a question that you could ask about the dataset. Hence, you're asking questions about StackOverflow questions:

Running the Project

• Run npm install to download the dependencies.
• Run npm test to run the tests. If you'd like, you can run npm run watch to automatically re-reun the tests when you make modifications.
• To test your application in your browser, or by using Postman, make sure you've installed nodemon via npm install -g nodemon and then run nodemon src/app.js. nodemon will keep the server running and automatically restart it if you change anything. You can now make requests to http://localhost:3000 in your browser or Postman!
• Make modifications to src/populate.js and src/server.js to make the tests pass.
• If you'd like, feel free to reference the tests in tests/populate.test.js and tests/server.test.js as you're developing.
• Once all tests have passed, you're done! Send us a pull request.

Instructions

StackOverflow questions and answers are both represented as post objects. Here are two example posts from posts.json, your dataset of StackOverflow posts. The first post is a question, whereas the second is an answer:

// this is a question
{
  "soID": 503093,
  "parentID": null,
  "url": "https://stackoverflow.com/q/503093",
  "title": "How to redirect to another webpage in JavaScript/jQuery?",
  "body": "<p>How can I redirect the user from one page to another using JavaScript or jQuery?</p>\n",
  "score": 6868,
  "tags": [
    "javascript",
    "jquery",
    "redirect"
  ],
  "acceptedAnswerID": 506004,
  "user": {
    "soUserID": 44984,
    "name": "venkatachalam",
    "reputation": 43478
  }
}

// this is an answer to the above question
{
  "soID": 506004,
  "parentID": 503093,
  "url": "https://stackoverflow.com/q/506004",
  "title": null,
  "body": "<h2>One does not simply redirect using jQuery</h2>\n\n<p>jQuery is not necessary, and <strong><code>window.location.replace(...)</code></strong> will best simulate an HTTP redirect.  </p>\n\n<p><code>window.location.replace(...)</code> is better than using <code>window.location.href</code>, because <code>replace()</code> does not keep the originating page in the session history, meaning the user won't get stuck in a never-ending back-button fiasco.</p>\n\n<blockquote>\n  <p>If you want to simulate someone clicking on a link, use\n  <strong><code>location.href</code></strong></p>\n  \n  <p>If you want to simulate an HTTP redirect, use <strong><code>location.replace</code></strong></p>\n</blockquote>\n\n<p><strong>For example:</strong></p>\n\n<pre><code>// similar behavior as an HTTP redirect\nwindow.location.replace(\"http://stackoverflow.com\");\n\n// similar behavior as clicking on a link\nwindow.location.href = \"http://stackoverflow.com\";\n</code></pre>\n",
  "score": 11159,
  "tags": [

  ],
  "acceptedAnswerID": null,
  "user": {
    "soUserID": 8985,
    "name": "Ryan McGeary",
    "reputation": 156833
  }
}

soID stands for StackOverflow ID, and is the unique numeric identifier that StackOverflow uses to discern its posts.

If the post's parentID field is null, that means the post is a question. By contrast, if parentID is not null, the post is an answer. For an answer, the parentID is the soID of the question that the post is answering.

Post Model

Start by editing src/post.js. Based on the posts given above, and the posts.json file if you need more examples, fill in the PostSchema. Fields soID, url, body, and score are required; all other fields are optional. Note that tags is an array of strings and user is a nested object; make sure you represent their schemas appropriately. Every field that is an id should be represented as a Number, not as an ObjectId, since these are not MongoDB references, but rather StackOverflow numeric identifiers.

Populate Posts

Now that you have a schema in place, populate MongoDB by adding all the posts in posts.json. To do this, fill in the function populatePosts() in src/populate.js. populatePosts() should read the posts array by calling readPosts(), which we've given to you. Then, it should save each post to the database. populatePosts() should return a promise that resolves only when all posts have successfully been added to the database.

Hints:

• Calling .save() on a Post model without any arguments will return a promise that resolves once that post is saved.
• Promise.all() will come in handy here.

After you write this function, make sure the populatePosts() populates all posts test passes (see tests/populate.test.js).

GET /accepted-answer/:soID

In src/server.js, add a route handler for GET /accepted-answer/:soID. When the client makes a GET request to /accepted-answer/:soID:

1. Find the question with the given soID (1 query).
2. Find the accepted answer of the question by using the acceptedAnswerID field (1 query).
3. Send back a JSON response with the single accepted answer post object.

You should only use 2 queries, and no more, for this route. If there's any error, or if there is no accepted answer, report it with an appropriate message and status code.

GET /top-answer/:soID

When the client makes a GET request to /top-answer/:soID:

1. Find the question with the given soID (1 query).
2. Find the answer of the given question that has the highest score and is not the accepted answer (1 query).
3. Send back a JSON response with the single top answer post object.

You should only use 2 queries, and no more, for this route. If there's any error, or if there is no top answer, report it with an appropriate message and status code.

GET /popular-jquery-questions

When the client makes a GET request to /popular-jquery-questions:

1. Find all question posts that are tagged with jquery and either have a score greater than 5000, or are posted by a user with reputation greater than 200,000 (1 query).
2. Send back a JSON response with an array of popular jquery questions.

You should only use 1 query, and no more, for this route. If there's any error, report it with an appropriate message and status code.

GET /npm-answers

When the client makes a GET request to /npm-answers:

1. Find all question posts that are tagged with npm (1 query).
2. Find all answers to all questions above (1 query).
3. Send back a JSON response with an array of answers to npm questions.

You should only use 2 queries, and no more, for this route. If there's any error, report it with an appropriate message and status code.

How many queries am I making?

Each time you construct a query with some Mongoose method (e.g. Post.find()) and introduce a callback that's called when you get results, that's 1 query. If you do this within a loop (e.g. a forEach), that's N queries, 1 per element of the array. For this assignment, you should not make any queries in a loop.

Constructing a complex query (e.g. Post.find().sort()) is still a single query so long as there is a single callback that listens for results.