Nodejs middleware .pre shows not a function - node.js

Question

var categoryList = new Referral({categoryList : category});
categoryList.pre('save', function (next) {
Referral.find({categoryList : category}, function (err, docs) {
if (!docs.length){
next();
}else{
console.log('Data exists: ', category);
next(new Error("Data exists!"));
}
})
})
Referral is my variable assigned to my schema.
categoryList is the object
This gives an error
TypeError: categoryList.pre is not a function at
D:\Aventyn\ClipCare_v2\app\api.js:112:18 at Layer.handle [as
handle_request]
(D:\Aventyn\ClipCare_v2\node_modules\express\lib\router\layer.js:95:5)
at next
(D:\Aventyn\ClipCare_v2\node_modules\express\lib\router\route.js:131:13)
at Route.dispatch
(D:\Aventyn\ClipCare_v2\node_modules\express\lib\router\route.js:112:3)
at Layer.handle [as handle_request]
(D:\Aventyn\ClipCare_v2\node_modules\express\lib\router\layer.js:95:5)
at
D:\Aventyn\ClipCare_v2\node_modules\express\lib\router\index.js:277:22
at Function.process_params
(D:\Aventyn\ClipCare_v2\node_modules\express\lib\router\index.js:330:12)
at next
(D:\Aventyn\ClipCare_v2\node_modules\express\lib\router\index.js:271:10)
at Function.handle
(D:\Aventyn\ClipCare_v2\node_modules\express\lib\router\index.js:176:3)
at router
(D:\Aventyn\ClipCare_v2\node_modules\express\lib\router\index.js:46:12)
at Layer.handle [as handle_request]
(D:\Aventyn\ClipCare_v2\node_modules\express\lib\router\layer.js:95:5)
at trim_prefix
(D:\Aventyn\ClipCare_v2\node_modules\express\lib\router\index.js:312:13)
at
D:\Aventyn\ClipCare_v2\node_modules\express\lib\router\index.js:280:7
at Function.process_params
(D:\Aventyn\ClipCare_v2\node_modules\express\lib\router\index.js:330:12)
at next
(D:\Aventyn\ClipCare_v2\node_modules\express\lib\router\index.js:271:10)
at
D:\Aventyn\ClipCare_v2\node_modules\express\lib\router\index.js:618:15

Answer 1

Try changing:
categoryList.pre('save', function (next) {
// ...
})
to:
categoryList.schema.pre('save', function (next) {
// ...
})
The .pre() is a method of the Mongoose schema, not a model.

Answer 2

Middleware (like pre hooks) are part of a schema. It looks like you're trying to use it on a single document, which is not how it works.
Instead, use it on the schema that you used to create the Referral model:
ReferralSchema.pre('save', ...);
This does mean that the pre hook will be applied to all documents of that schema.