Sails.js oneToOne pointing to last on oneToMany - associations

Question

A design wonder in sails.js and waterline models.
I have a "bear" model and a "location" one. They hold a oneToMany association ("bear can have multiple location over time").
bear.js
module.exports = {
attributes: {
location: {
collection: 'location',
via: 'bear'
}
}
};
location.js
module.exports = {
attributes: {
timestamp: {
type: 'datetime',
required: true
},
bear: {
model: 'bear'
}
}
};
I'm trying to make a "oneToOne" association grabbing the last location of a bear (lastLocation), and wondering what's the best solution :
Trying to override ToJSON on bear, fetching last location (doesn't seem to work, because ToJSON is hardly synchronous so I can't make it wait for an asynchronous find)
Creating a real oneToOne relationship and adding a hook AfterCreate on location to update that "lastLocation" association ?
Override blueprint create on location ?
Override blueprint add on bear ?
Any other idea ?
Thanks =)

Answer 1

I think this is your answer here?
Creating a real oneToOne relationship and adding a hook AfterCreate on location to update that "lastLocation" association ?
You should create an additional attribute on bear called lastLocation:{model:'location'}, and automatically update that after each location is created on the associated bear. Their are otherways to do this, but if the last location is something that is read a lot, then this will probably be your best approach.
Now this is a little bit of opinion based as there would be many factors involved in your design to say for sure, but I think you will be fine using this approach.

Answer 2

Here is what I ended up with :
model/Bear.js - last location association
lastLocation: {
model: 'location'
}
model/Location.js - afterCreate hook
afterCreate: function(insertedLocation, callback) {
if(!insertedLocation.bear) {
return callback();
}
Bear.findOneById(insertedLocation.bear, function(err, bear) {
if(err) {
return callback(err);
}
Location.findOneById(bear.lastLocation, function(err, oldLastLocation) {
bear.lastLocation = insertedLocation.id;
bear.save(function(err) {
return callback(err);
});
});
});
}
the if(!insertedLocation.bear) test is the key
I repeated similar code inside afterUpdate hook
afterUpdate: function(updatedLocation, callback) {
if(!updatedLocation.bear) {
return callback();
}
Bear.findOneById(updatedLocation.bear, function(err, bear) {
if(err) {
return callback(err);
}
Location.findOneById(bear.lastLocation, function(err, oldLastLocation) {
bear.lastLocation = updatedLocation.id;
bear.save(function(err) {
return callback(err);
});
});
});
}
adding a test in order to prevent updating bear each time we update lastLocation
One could add some PublishUpdate() logic