meteor, using _.map when joining collections - mongodb

Question

Here is my helpers to diplay data from two collections
Template.Lirescategorie.helpers({
scategories: function () {
var cursor = Scategories.find();
var data = [];
cursor.forEach(function(somewhat) {
var categories = Categories.findOne({_id : somewhat.categorieID}, {categorie:1});
data.push({cat : categories.categorie, scat : somewhat.scategorie });
});
return data;
}
});
Here are my collections
categorie :
{
"_id": "LBKZQfZZSf4DRdeXo",
"categorie": "Citoyenneté"
}
scategorie
{
"_id": "cNHYpAEvC9ffjWkf5",
"categorieID": "LBKZQfZZSf4DRdeXo",
"scategorie": "Etat-Civil"
}
I'm pretty sure my helpers' code is not optimal. And i think by using _.map or something like that i can reduce the code.
Since i'm not really familiar to it, i'm looking for help about this.

Answer 1

Welcome to client-side joins. You can use .map() to get the list of categorieIDs and do the second find in one go with $in::
var cursor = Scategories.find();
var arrayOfCategorieIDs = cursor.map(function(s){return s.categorieId});
var categories = Categories.find({_id : {$in: arrayOfCategorieIDs}});
Then:
var sCategories = cursor.map(function(s){return s.scategorie}); // array of scategorie names
var categoryNames = categories.map(function(c){return s.categorie}); // array of categorie names
Then assemble these two arrays of strings into the array of objects you're looking for.
But there's a far simpler pattern for a client-side join: just iterate over one cursor and do the lookup into the related collection in a helper. For example:
html:
{{#each sCategories}}
{{sCategorie}}
{{categorie}}
{{/each}}
js:
Lirescategorie.helpers({
sCategories:(){
return Scategories.find();
},
categorie:(){
return Categories.findOne(this.categorieID).categorie;
}
});