Run custom validation in mongoose update query - node.js

Question

I have been trying to run a custom validator to check if the name entered by the user already exists in the database. Since, mongoDb treats uppercase and lowercase names as different, I created my own validator for it.
function uniqueFieldInsensitive ( modelName, field ){
return function(val, cb){
if( val && val.length ){ // if string not empty/null
var query = mongoose.models[modelName]
.where( field, new RegExp('^'+val+'$', 'i') ); // lookup the collection for somthing that looks like this field
if( !this.isNew ){ // if update, make sure we are not colliding with itself
query = query.where('_id').ne(this._id)
}
query.count(function(err,n){
// false when validation fails
cb( n < 1 )
})
} else { // raise error of unique if empty // may be confusing, but is rightful
cb( false )
}
}
}
Now, the problem is that the validator runs while saving the document in the DB but not while update.
Since, I am using mongoose version 4.x, I also tried using { runValidators: true } in my update query. That doesn't work either as the 'this' keyword in my validator is 'null' while in the case of update whereas it refers to the updated doc in the case of save.
Could you please let me know if there is something i missed or is there any other way by which I can run custom validators in update query.

Answer 1

Finally I found a way out to do this.
According to MongoDB documentation, it says:
First, update validators only check $set and $unset operations. Update validators will not check $push or $inc operations.
The second and most important difference lies in the fact that, in document validators, this refers to the document being updated. In the case of update validators, there is no underlying document, so this will be null in your custom validators.
Refer to : Validators for update()
So, now we are only left with calling save() instead of update() in our queries. Since, save() calls all the custom and inbuilt validators, our validator will also be called. I achieved it like this:
function(req, res, next) {
_.assign(req.libraryStep, req.body);
req.libraryStep.save().then(function(data){
res.json(data);
}).then(null, function (err) {
console.info(err);
var newErr = new errorHandler.error.ProcessingError(errorHandler.getErrorMessage(err));
next(newErr);
});
};
Notice here req.libraryStep is the document that i queried from the database. I have used lodash method assign which takes the updated json and assigns it to the existing database document.
https://lodash.com/docs#assign
I dont think this is the ideal way but as for now till Mongoose doesnt come up with supporting custom validators, we can use this to solve our problem.

Answer 2

This is a fairly old thread, but I wanted to update the answer for those who come across it like I did.
While you're correct about the context of this being empty in an update validator (per the docs), there is a context option you can use to set the context of this. See the docs
However, a plugin also exists that will check the uniqueness of the field you are setting: mongoose-unique-validator. I use this for checking for duplicate emails. This also has an option for case insensitivity, so I would check it out. It also does run correctly using the update command with the runValidators: true option.