How to properly design a Mongo Schema to keep elements that belong together - together? - mongodb

Question

var FamilySchema = new Schema({
members: [String],
indexedOn: {
type: Date,
default: Date.now
},
updatedOn: {
type: Date,
default: Date.now
}
});
As a crude example, I have a Family that has many members, so I use a schema like the one shown above. But there can be THOUSANDS of members in one family and a member can be in ONLY one family. So every time I come across a new member, I have to search to see if he belongs to any Families and if he does, add him. If he doesn't, I have to create a new family and add him.
This seems like an extremely inefficient way to do things. Is there a better design for this sort of use case?

Answer 1

You could use an array and index the field of members.
Or, here's a very common MongoDB modeling technique that avoids using an array (and means that you can have richer structures for a given family member). Create a Family and a FamilyMember. As you said that each family member may only be in one family, you would add a field to the FamilyMemberSchema as a reference to the Family (using ref as shown below).
var FamilySchema = new Schema({
name: String,
indexedOn: {
type: Date,
default: Date.now
},
updatedOn: {
type: Date,
default: Date.now
}
});
var FamilyMemberSchema = new Schema({
name: String,
family_id: { type: Schema.Types.ObjectId, ref: 'Family' }
});
// you might want an index on these fields
FamilyMemberSchema.index({ family_id: 1, name: 1});
var Family = mongoose.Model('Family', FamilySchema);
var FamilyMember = mongoose.Model('FamilyMember', FamilyMemberSchema);
You could then use a query to fetch all Family Members for a particular family:
FamilyMember.find().where('family_id', 'AFAMILYID').exec(/* callback */);
You wouldn't need to use the ref much as using the populate functionality wouldn't be particularly useful in your situation (http://mongoosejs.com/docs/populate.html), but it documents the schema definition better, so I'd use it.

Answer 2

You can use two collections, one for families and other for members. You can use a field in members collection in order to link them with one family (by "_id" for instance) of the other collection.
When you have to add new element you can search on "members" collections if the element already exists. An index could help to speed up the query.