Relationship field within same collection? - mongodb

Question

I have a keystonejs model for product categories (MongoDB). Some categories should have subcategories. Currently I have set a relationship field "ChildCategoryOf", where I can manually select the Parent Category in admin panel. To have more functionality, I would like to create another Field called "ParentCategoryOf" that would consist an Array of subcategories. How is it possible to have a field that automatically stores Child categories in Array? I imagine it like this:
Current model:
let ProductCategory = new keystone.List('ProductCategory', {
autokey: {
from: 'name',
path: 'key',
unique: true
}
});
ProductCategory.add({
name: {
type: String,
required: true
},
ChildCategoryOf: {
type: Types.Relationship,
ref: 'ProductCategory',
many: false,
required: false,
},
IsParentCategory: Types.Boolean,
});

Answer 1

For categories in mongo you can use an inheritance like model, in which you can store the parentId and ancestor Id for each model and its children and then add a method to the mongoose model to add a child each time you call it on an instance, this would be like below code:
const ProductCategory = new Schema({
name: String,
parent: { type: Schema.Types.ObjectId, ref: 'ProductCategory'},
ancestors: [{type: Schema.Types.ObjectId, ref: 'ProductCategory'}],
children: [{type: Schema.Types.ObjectId, ref: 'ProductCategory'}]
});
ProductCategory.methods = {
addChild: function(child){
let that = this;
child.parent = this._id;
child.ancestors = this.ancestors.concat([this._id]);
return this.model('ProductCategory').create(child).addCallback
(function(child){
that.children.push(child._id);
that.save();
});
}
};
then later from where you want to find products by their categories you should concat the category id that you find with it's children ids and use this array in find query with $in operator to find all the products in a category with its children.