Mongoose: insert one collection depenting on an other with promises - mongodb

Question

I need to insert records in two collections. The second collection stores the ID of records of the first collection. It is a 1:m (fisrt:second) situation. The trigger is the second collection:
If a record for the second collection needs to be stored
check if there is already a fitting record in the first collection
if not: then save one in the first collection
store the second collection
save the id of the record of the first collection in the second collection
The following example seems to fullfill these steps. But I have the promises only half way.
How can this be done in a better "promised" way?
saveObjects(name: String, objects: Array<IObject>){
var promise = FirstModel.findOne({Name : name}).exec();
promise.then(function(res1){
if (!res1){
var la = new FirstModel();
la.Name = name;
la.save(function(err){
if (err) throw err;
})
}
}).error(function(err){
throw err;
})
objects.forEach(function(obj) {
FirstModel.findOne({Name : name},'_id',function(err, res2){
if (err) throw err;
var vo = new SecondModel();
vo.Name = name;
vo.FistID = res2._id;
vo.save(function(err){
if (err) throw err;
});
});
});
}

Answer 1

I'm gona assume here that you're using bluebird or another promise equivalent set up.
var Promise = require('bluebird');
saveObjects(name: String, objects: Array < IObject > ) {
// Get the first model
return FirstModel
.findOne({
Name: name
})
.exec()
.then(function (res1) {
if (!res1) {
var la = new FirstModel();
la.Name = name;
return la.save() // We return the save operation on the model, save() returns a promise
}
// We just return the model normally so it passes down the chain.
return res1;
})
.then(function (res1) {
// Here we use Promise.all() method on bluebird which accepts an Array
// of promises, we create a promise from the objects array by using Array.map() which
// goes through every object in the array and creates a new array.
return Promise
.all(objects.map(function (obj) {
// We go through each object in objects and create a new
// model and return the save() method of each model, this
// creates a array of promises which are resolved when each
// all model has been saved.
var vo = new SecondModel();
vo.Name = name;
vo.FistID = res1._id;
return vo.save();
}));
})
.then(function (models) {
// here we have all the models we just saved in an array called models,
// do what you want with it.
})
.error(function (err) {
throw err;
})
}
For more info see documentation on Array.map() here and Promise.all() here