express-validator to validate parameter which is an array - node.js

Question

I am using express-validator to validate POST data in my express application. I have a form which has a select where in user can select multiple options:
<select name="category" multiple id="category">
<option value="1">category 1 </option>
.......
</select>
The payload after submitting form shows me this if I select multiple values:
...&category=1&category=2&....
Now, in my Express application I try to validate it like this:
req.checkBody('category', 'category cannot be empty').notEmpty();
But, even after I send multiple values I always get the error - category cannot be empty. If I print my variable as req.body.category[0] - I get the data. But, somehow not able to understand the way I need to pass this to my validator.

Answer 1

You may need to create your own custom validator;
expressValidator = require('express-validator');
validator = require('validator');
app.use(expressValidator({
customValidators: {
isArray: function(value) {
return Array.isArray(value);
},
notEmpty: function(array) {
return array.length > 0;
}
gte: function(param, num) {
return param >= num;
}
}
}));
req.checkBody('category', 'category cannot be empty').isArray().notEmpty();

Answer 2

Try this:
router.post('/your-url',
[
check('category').custom((options, { req, location, path }) => {
if (typeof category === 'object' && category && Array.isArray(category) && category.length) {
return true;
} else {
return false;
}
})
],
controller.fn);

Answer 3

Answering a bit late but hope this might help somebody.
If you are using express-validator, You can pass minimum / maximum length option to check whether Array is empty or exceeds a certain limit
req.checkBody('category', 'category cannot be empty').isArray({ min: 1, max: 10 });

Answer 4

If you are using schema, you can do it this way:
const schema = {
someArray: { isArray: true, notEmpty: true }
};

Answer 5

This maybe a bit late but for others who wants a clean solution without using the customValidator, I created a validator that can dig up to the deepest array and validate its content.
https://github.com/edgracilla/wallter
In your case validation would be:
const halter = require('wallter').halter
const Builder = require('wallter').builder // validation schema builder
const builder = new Builder()
server.use(halter())
server.post('/test', function (req, res, next) {
let validationSchema = builder.fresh()
.addRule('category.*', 'required')
.build()
// validationSchema output:
// { 'category.*': { required: { msg: 'Value for field \'category.*\' is required' } } }
req.halt(validationSchema).then(result => {
if (result.length) {
res.send(400, result)
} else {
res.send(200)
}
return next()
})
})
Error message can be override in builder initialization. Check the repo README.md for an in depth usage.