Overriding Mongoose _id and using properties directly from the schema - mongodb

Question

I need to create a patient model and override the _id property. I know I can override it by writing a schema like so:
const PatientSchema: Schema = new Schema({
_id: {type: String, required: true},
name: { type: String, required: true },
surname: { type: String, required: true },
provider: { type: Schema.Types.ObjectId, ref: "Provider" },
});
Is there a way to define the _id property inside the schema to reference the name + surname properties?:
_id: name+surname, (?)
or do I have to explicitly define it when creating and saving a new model?:
const patient = new Patient();
patient._id = name+surname;
Also, what should I consider if patients have the same name and surname? What is considered best practice in this case if the _id needs to = name + surname?
Thanks

Answer 1

you could use mongoose pre-save middleware in your schema
Basically, middlewares are functions that are called during the execution of a model query/method.
there are 2 types of middleware :
"pre" middlewares that are executed before the query
"post" middlewares that are executed after the query.
syntax :
schema.pre([method], function (next) {
console.log("pre middleware")
next();
});
schema.post([method], function (next) {
console.log("post middleware")
next();
});
/*[method] can be
"save","updateOne","findOne","findOneAndUpdate",etc...*/
//"pre" will always be executed before "post"
And depending on the method you are going to use, middlewares can change in the value of "this", there are 4 types of these:
where "this" refers to the document E.g."save"
where "this" refers to the query E.g."findOne"
where "this" refers to an aggregate E.g." aggregate"
where "this" refers to the model. E.g. "insertMany"
Solution :
const PatientSchema = new Schema({
_id: { type: String },
name: { type: String, required: true },
surname: { type: String, required: true },
provider: { type: Schema.Types.ObjectId, ref: "Provider" },
});
//will change _id before save
PatientSchema.pre("save", async function (next) {
try {
const patient = this; //the target document
patient._id = patient.name + " " + patient.surnam
next()
}
catch (err) { next(err) }
});
module.exports = model("Patients", PatientSchema);
and when you create a patient it will have the id based on the combination of their first and last name
const patient = new Patient({
name: "John",
surname: "smith"
})
await patient.save();
result : {
_id: "John smith ";
name: "John";
surname: "smith";
__v: 0;
}
[ Edit ]
if you want your id to be unique you could create an ObjectId and concatenate
it to the final id
const { ObjectId } = require("mongodb");
PatientSchema.pre("save", async function (next) {
try {
const patient = this; //the target document
const objectId = ObjectId();
patient._id = `${patient.name} ${patient.surname} ${objectId}`;
next();
} catch (err) {
next(err);
}
});