Mongoose - remove _id from lean ( using toJSON() ?) - node.js

Question

I'm having a NODE.JS project using mongoose 5.x
My model have toJSON method which removes the _id & __v fields perfectly
mySchema.method("toJSON", function toJSON() {
const {__v, _id, ...object} = this.toObject();
return {
id: _id,
...object
};
});
so when fetching data from the db:
const data = myModel.findOne({_id: id});
I get an object that when serialized to the user:
res.json(data);
It doesn't contain the _id and __v fields as required.
The problem is when I use lean():
const data = myModel.findOne({_id: id}).lean();
the data object contains those fields.
I can remove them manually when using lean
but I would prefer to find a way to sanitize the data object in both cases with the same mechanism.
any suggestions?
Thanks in advance.

Answer 1

Not sure if this is what you want but maybe:
const data = myModel.findOne({_id: id}).lean().then(res => {
delete res._id
return res
})

Answer 2

When JSON.stringify() is called on an object, a check if done if it has a property called toJSON. It's not specific to Mongoose, as it works on plain objects:
const myObj = {
_id: 123,
foo: 'bar',
// `toJSON() {...}` is short for `toJSON: function toJSON() {...}`
toJSON() {
// Because "this" is used, you can't use an arrow function.
delete this._id;
return this;
}
};
console.log(JSON.stringify(myObj));
// {"foo":"bar"}
Mongoose doesn't have an option to automatically inject a toJSON function into objects returned by lean(). But that's something you can add.
First, create a function that:
Takes an object with properties
Listens to when Mongoose runs a find query
Tells Mongoose that after the query, it should change the result
The change: merge the result with the object from step 1.
function mergeWithLeanObjects(props) {
// Return a function that takes your schema.
return function(schema) {
// Before these methods are run on the schema, execute a function.
schema.pre(['find', 'findOne'], function() {
// Check for {lean:true}
if (this._mongooseOptions.lean) {
// Changes the document(s) that will be returned by the query.
this.transform(function(res) {
// [].concat(res) makes sure its an array.
[].concat(res).forEach(obj => Object.assign(obj, props));
return res;
});
}
});
};
}
Now add it to your schema:
mySchema = new mongoose.Schema({
foo: String
});
mySchema.plugin(mergeWithLeanObjects({
toJSON() {
delete this._id;
delete this.__v;
return this;
}
}));
Then test it:
const full = await myModel.findOne();
const lean = await myModel.findOne().lean();
console.log(full);
// Logs a Mongoose document, all properties.
{ _id: new ObjectId("62a8b39466768658e7333154"), foo: 'bar', __v: 1 }
console.log(JSON.stringify(full));
// Logs a JSON string, all properties.
{"_id":"62a8b39466768658e7333154","foo":"bar","__v":1}
console.log(lean);
// Logs an Object, all properties.
{ _id: new ObjectId("62a8b39466768658e7333154"),
foo: 'bar', __v: 1, toJSON: [Function: toJSON] }
console.log(JSON.stringify(lean));
// Logs a JSON string, filtered properties.
{"foo":"bar"}
If you want to re-use the plugin with the same settings on multiple schemas, just save the function that mergeWithLeanObjects returns somewhere.
// file: clean.js
module.exports = mergeWithLeanObjects({
toJSON() {
delete this._id;
delete this.__v;
return this;
}
});
// file: some-schema.js
schema1.plugin(require('./clean.js'));
// file: some-other-schema.js
schema2.plugin(require('./clean.js'));
There's also mongoose.plugin() to add the function to all schemas.

Answer 3

Try this to retrieve the _id from a document
myModel.findOne({_id: id}, function(err, doc) {
if(err)
return 'do something with this err'
console.log(doc._id)
})