Express with mongodb find one - node.js

Question

Im new to nodejs , express and mongodb.
I got stuck at the findOne function using ObjectId of mongodb
With the code below, I got the error : "Error: Argument passed in must be a single String of 12 bytes or a string of 24 hex characters"
Im using lastest version of everything (because Im new to them)
My code in view:
<% for(var i = 0 ; i < posts.length; i++ ) { %>
<% post = posts[i] %>
<article class="post">
<div class="post-preview col-xs-10 no-gutter">
<h2>
<a href="/posts/<%=i%>">
<%= post.title %>
</a>
</h2>
<p><%= post.description %></p>
<p class="meta">
<%= post.author.name %> in
<%= post.category.name %> <i class="link-spacer"></i> <i class="fa fa-bookmark"></i> <%= post.created_at %>
</p>
</div>
<div class=" col-xs-2 no-gutter">
<img src="<%= post.author.image %>" class="user-icon" alt="user-image">
</div>
</article>
<% } %>
Please tell me what's wrong with my code .
p/s : the req.params.id is valid and logable.

Answer 1

Default mongo IDs don't increment from 1. They will look like "_id" : ObjectId("5908f94c06515dfa8522459c") in the database. Your problem is your href is navigating by index, not the id itself. You need to change:
<a href="/posts/<%=i%>">
<%= post.title %>
</a>
to:
<a href="/posts/<%=post._id%>">
<%= post.title %>
</a>
this will make your link /posts/5908f94c06515dfa8522459c instead of /posts/1

Answer 2

I'm guessing it's because the id is a string of not 12 bytes (nor 24 hex characters). When the URL comes in to your express web server, it's a string. When express matches a part of it and stores it, there's no rule that :id couldn't be myCoolId, which isn't a number.
So everything in req.params is a string. I would add some checking to make sure it's a number, cast it, and then give it to ObjectId.
EDIT: If you want to work with it as strings, then try some of the following:
const ObjectID = require('mongodb').ObjectID;
// When making a brand new record, just use a new object id.
let record = new ObjectID();
console.log(record);
// When giving the ID to the client as a string, make it a hex string.
let hexString = record.toHexString();
console.log(hexString);
// You can validate that it's a valid object id in your route when they post it back.
let valid = ObjectID.isValid(hexString);
console.log(valid);
// Then you can turn it back into an object id.
let fromHex = ObjectID.createFromHexString(hexString);
console.log(fromHex);