Cast to ObjectId failed for value "req.params.id" at path "_id" for model "Project" - node.js

Question

I am trying to create a clone of employee management system. I want to implement a feature that when admin opens a details page for any project he will get list of available employees as checkboxes and when select them and submit then those employees will be added to the given project.
I am developing it using Node.js and MongoDB
My project schema is -
const ProjectSchema = new mongoose.Schema({
name: String,
deadline: Date,
description: String,
manager:{
id: {
type: mongoose.Schema.Types.ObjectId,
ref: "User"
},
},
employees: [
{
type: mongoose.Schema.Types.ObjectId,
ref: "User"
}
],
created_on: {
type: Date,
default: Date.now
}
});
Form -
<form action="/admin/project/<%= project._id %>/addmembers" method="POST">
<div class="row">
<% employees.forEach((employee) => { %>
<% if(!employee.projects.includes(project._id)){ %>
<div class="col-12 col-sm-6 col-md-4 col-xl-3">
<input type="checkbox" value="<%= employee._id %>" name="newMembers"> <%= employee.name %> </input>
</div>
<% } %>
<% }); %>
</div>
<hr class="my-2">
<p class="lead">
<button class="btn btn-blue btn-lg">Add Members</button>
</p>
</form>
Code for handling the request -
router.post("/project/:id/addmembers", (req, res) => {
console.log("add member post route");
Project.findById(req.params.id, (err, foundProject) => {
if(err){
console.log(err);
req.flash("error", err.message);
res.redirect("back");
} else {
req.body.newMembers.forEach((employee) => {
foundProject.employees.push(employee);
})
foundProject.save()
console.log(foundProject);
req.flash("success", "Successfully added new members");
res.redirect("/admin/project/req.params.id");
}
})
});
Now whenever I submit form users are added but I always get an error Cast to ObjectId failed for value "req.params.id" at path "_id" for model "Project" instead of success message now I am new to mongo so I googled it but can't solve my problem can anyone explain me why this error is coming and how can I fix it?
Also I know that if if only one checkbox is selected then req.body.newMembers will not be array. If you can you provide better method to do it, it will be very helpful?
Update -
I also tried findOne(), find(), findByIdAndUpdate(), and id = mongoose.Types.ObjectId(req.params.id) but still get the same error message

Answer 1

It looks like what is happening is you aren't properly handling ids and _id. Given that you haven't mentioned anything, I assume you see this error only once. However, given that the error has to do with the project model/schema, and you use almost the same code for both manager and employees, the error should have to do with a difference between the two. The main difference I see is manager has id: {*id stuff*}, but employee has {*id stuff*} with no id:. However, I don't think this is the actual error, but just something to keep in mind. Try also changing the id type to something like number just to see if this is related to the issue.
What I think that actual error is is the fact that you use req.params.id in a findById(). This searches your database using the _id. First, having id and _id both is a bit redundant (if you have a reason, that's fine, but _id is something MongoDB needs, so it might be better to just stick with it as it is precreated and handled). Second, you are using a string/int as an id search. To test whether this is the issue, try changing findById() to something like findOne() or find(). Just to clarify, findById() doesn't explicitly need an ObjectId, so the type may not be the issue, but findById() does handle the search differently than find({_id: id}).
Another thing to check is that req.params.id actually gives the right value. It should, but this is something to verify. To do so, just console.log() it. If this is the problem, try moving :id to the end of the path.
In response to your edit:
Make sure that the problem doesn't have to do with not having id: in the employee (as stated above) and that it doesn't have to do with the id being a ObjectId rather than a number. If you change the id to a number, make sure to change the search so that it finds the object by id not _id. Just to let you know, every MongoDB object has an _id (even subobjects like employee and manager), so using id is somewhat redundant.
To give you more things to try: make sure you console.log() req.params.id to make sure it has the right value. Then, also try commenting sections of code until you find which line it is on. Try hardcoding some input until it works.