In MongoDb, are sub documents references or extensions - mongodb

Question

Using mongoose you can create a sub document as such:
export const UserSchema = new Schema({
email: {
type: String,
unique: true,
required: "email is required.",
match: [/^\w+([\.-]?\w+)*#\w+([\.-]?\w+)*(\.\w{2,3})+$/, 'Please fill a valid email address']
},
firstName: {
type: String,
required: "firstName is required."
},
lastName: {
type: String,
required: "lastName is required."
},
dateOfBirth: {
type: Date,
required: "dateOfBirth is required."
},
roles: [{
role: String,
required: "role is required",
validate: isValidUserRole
}],
address: AddressSchema,
});
Address Schema
export const AddressSchema = new Schema({
streetAddress: {
type: String
},
addressLine2: {
type: String
},
city: {
type: String
},
state: {
type: String
},
zipCode: {
type: String
},
country: {
type: String
}
});
Whenever I save a user, will mongoose create a new user document with nested address data or a user and address and then reference that address document within the user instance?
How would I approach the case of 2 users sharing the same address?
Thanks!

Answer 1

You need not to provide the AddressSchema in the UserSchema schema.
You can just provide reference of AddressSchema like the following.
export const UserSchema = new Schema({
email: {
type: String,
unique: true,
required: "email is required.",
match: [/^\w+([\.-]?\w+)*#\w+([\.-]?\w+)*(\.\w{2,3})+$/, 'Please fill a valid email address']
},
firstName: {
type: String,
required: "firstName is required."
},
lastName: {
type: String,
required: "lastName is required."
},
dateOfBirth: {
type: Date,
required: "dateOfBirth is required."
},
roles: [{
role: String,
required: "role is required",
validate: isValidUserRole
}],
address: {type:mongoose.Schema.Types.ObjectId,ref:'AddressSchema',required:true}
});
But remember that in order to make this work, 1st you need to create an Address data and provide their _id in UserSchema.
What happens by the above method is,
AddressSchema's ObjectId(_id) works as the REFERENCE in UserSchema. Basically, it acts as a REFERENCE DOCUMENT in UserSchema

Answer 2

You can find this out by querying your data through mongo shell.
When a document contains an embedded document (this is indistinguishable from nested hashes in the shell), the embedded document wholly belongs to the top level document and cannot be included-by-reference into another document.