Can I define a custom validation with options for Loopback? - loopbackjs

Question

Is there a prescribed way to create a custom validator in loopback? As an example, assume that I want to create something like:
Validatable.validatesRange('aProperty', {min: 0, max: 1000})
Please note that I am aware of:
Validatable.validates(propertyName, validFn, options)
The problem I have with validates() is that validFn does not have access to the options. So, I'm forced to hard code this logic; and create a custom method for every property that needs this type of validation. This is undesirable.
Similarly, I am familiar with:
Model.observes('before save', hookFn)
Unfortunately, I see no way to even declare options for the hookFn(). I don't have this specific need (at least, not yet). It was just an avenue I explored as a possible alternative to solve my problem.
Any advice is appreciated. Thanks in advance!

Answer 1

There is a mention of how to do this over at https://docs.strongloop.com/display/public/LB/Validating+model+data
You can also call validate() or validateAsync() with custom validation
functions.
That leads you to this page https://apidocs.strongloop.com/loopback-datasource-juggler/#validatable-validate
Which provides an example.
I tried it out on my own ...
Question.validate('points', customValidator, {message: 'Negative Points'});
function customValidator(err) {
if (this.points <0) err();
}
And since that function name isn't really used anywhere else and (in this case) the function is short, I also tried it out with anonymous function:
Question.validate('points',
function (err) { if (this.points <0) err(); },
{message: 'Question has a negative value'})
When points are less than zero, it throws the validation error shown below.
{
"error": {
"name": "ValidationError",
"status": 422,
"message": "The `Question` instance is not valid. Details: `points` Negative Points (value: -100).",
"statusCode": 422,
"details": {
"context": "Question",
"codes": {
"points": [
"custom"
]
},
"messages": {
"points": [
"Negative Points"
]
}

Answer 2

What you are looking for is validatesLengthOf(). For example:
Validatable.validatesLengthOf('aProperty', {min: 0, max: 1000});
Here is the documentation links:
All the methods of Validatable class and
Model-wise validation.