sequelize handling rejection in the create statement - catch not firing - node.js

Question

The sequelize create statement has an error and I would like to handle that error. Since the create statement has the error I need to handle promise rejection. How do I do that in code? Tried to look at the sequelize documents but unable to work it out.
db.Employee.create(empData,
{
include:[
{
model: db.EmployeeDetails
}
]
}).then(function(newEmployee){
res.json(newEmployee);
}).catch(function(err){
return next(err);
});
The error is on the create and so the webpage just gives an internal server error. I was under the impression that the catch was something that handled the promise rejection and failure. In this case, how can I handle the promise rejection in code. An example would be greatly appreciated.

Answer 1

By doing next(err), by default, you send a 500 Internal Server Error message. If you use Express, and want to show a custom error, just append a status code which is not 5xx to the error:
General Usage:
const err = new Error("my custom error")
err.statusCode = 400
next(err)
In your snippet, do:
db.Employee.create(empData, {
include:[
{
model: db.EmployeeDetails
}
]
}).then(function(newEmployee){
res.json(newEmployee);
}).catch(function(err){
err.statusCode = 400
next(err);
});
If you haven't set your error handler in Express you will need to add somewhere at the end of the main file this:
// Error Handler
app.use(function(err, req, res, next) {
console.error(err)
if (!err.statusCode) err.statusCode = 500;
let msg = err.message
// Do not expose 500 error messages in production, to the client
if (process.env.NODE_ENV === "production" && err.statusCode === 500) {
msg = "Internal Server Error"
}
res.status(err.statusCode).send(msg)
})

Answer 2

Your webpage showing a 500 error means the issue was caught / working as intended. What you need to do is figure out how to handle displaying that error in a pretty format - this being a UI task. If you want a 'patch' for hiding the issue, change your return to a res. This will trick your browser with a 200 status and hide the error.
I do want to add, I recommend trying async/await for sequelize. There's a good amount of usage examples with it.
Promise
db.Employee.create(empData,
{
include:[
{
model: db.EmployeeDetails
}
]
}).then(function(newEmployee){
res.json(newEmployee);
}).catch(function(err){
// Temporary patch
res.json("pretty error message");
});
Async/Await version
async function createEmployee(empData) {
try {
return await db.Employee.create(empData, {
include:[ { model: db.EmployeeDetails } ]
});
} catch (err) {
// Handle error here
return err;
}
}