sails.js一对多关系-变量所有者集合属性

Question

On sailsjs.org's documentation, a one to many relationship for the owning side is defined like this

//user.js
module.exports = {
    attributes: {
        name:'STRING',
        age:'INTEGER',
        pets:{
            collection: 'pet',
            via: 'owner'
        }
    }
}

'pet' is a constant, with a consistent schema on SQL databases. What if I want to have a superclass pet and subclasses with unique attributes(different number of rows)? Say I have an octopus and a dog. Dogs have 4 legs and 2 ears. Octopus have 8 tentacles. The only commonality will be abstracted into the pet class(color, name, age).

If this is not possible, I would have to resort to something like this no?

//user.js
module.exports = {
    attributes: {
        name:'STRING',
        age:'INTEGER',
        dogs:{
            collection: 'dog',
            via: 'owner'
        },
        octopuses:{
            collection: 'octopus',
            via: 'owner'
        }
    }
}

However, this could get quite messy if I wanted to introduce more pets like eagle(can fly), parrot(can talk), and would result in many nulls if I was to use a SQL database. Perhaps mongoDB would be ideal for this?

Answer 1

In Waterline each model is treated as a table in a SQL database or a Collection in Mongo. If a Dog will have completely different attributes from an Octopus then yes you would break those into separate tables and link them to the User. I think the easiest way would to just add a type attribute to the Pet model.

// user.js
module.exports = {
    attributes: {
        name:'STRING',
        age:'INTEGER',
        pets:{
            collection: 'pet',
            via: 'owner'
        }
    }
}

// pet.js
module.exports = {
    attributes: {
        name:'STRING',
        type: 'STRING',
        owner:{
            model: 'user'
        }
    }
}

This would allow queries such as:

User.find().populate('pets', { type: 'dog' });

Another option would be to store the pet attributes in a json object. This isn't currently searchable but would allow you to store various things about the pets in a denormalized fashion.

// pet.js
module.exports = {
    attributes: {
        name:'STRING',
        type: 'STRING',
        characteristics: {
            type: 'json'
        },
        owner:{
            model: 'user'
        }
    }
}

Which would allow you to have pets that look like the following:

[{
    id: 1,
    name: 'fluffy',
    type: 'dog',
    characteristics: {
        food: 'mice',
        limbs: 4,
        fur: 'white'
    },
    owner: 1
},
{
    id: 2,
    name: 'inky',
    type: 'octopus',
    characteristics: {
        habitat: 'ocean'
        tentacles: 8,
        canChooseWorldCupWinners: true
    },
    owner: 1
}]