Building multi level menu using nodejs - node.js

Question

I currently have the following data in my database
The Mongo database stores like this
id parent
1 0
2 0
3 1
4 1
5 2
6 2
7 2
30 3
31 3
70 7
71 7
Now I want the output in a single javascript array like so using nodejs
[
{id:1,sub:[
{id:3, sub:[{id:30},{id:31}]},
{id:4,sub:[]}
]
},
{id:2,sub:[
{id:5,sub: []},
{id:6,sub: []},
{id:7,sub: [{id:70}, {id:71}]}
]
}
]
The purpose of this is basically to output the category in a megamenu.

Answer 1

The following example shows a way to do what you want.
// Example data from the question
var nodes = [
{ id: 1, parent: 0 },
{ id: 2, parent: 0 },
{ id: 3, parent: 1 },
{ id: 4, parent: 1 },
{ id: 5, parent: 2 },
{ id: 6, parent: 2 },
{ id: 7, parent: 2 },
{ id: 30, parent: 3 },
{ id: 31, parent: 3 },
{ id: 70, parent: 7 },
{ id: 71, parent: 7 }
];
// We construct `t`, the array of parents, so that `t[i] === x` means that `x`
// is the parent of `i`
var t = [];
for (var i = 0; i < nodes.length; i++) {
t[nodes[i].id] = nodes[i].parent;
}
// `t` represents the array of parents
// `c` represents the parent whose children should be put in the outputted array
function f(t, c) {
// The output structure
var a = [];
// We loop through all the nodes to fill `a`
for (var i = 0; i < t.length; i++) {
// If the node has the parent `c`
if (t[i] === c) {
// Create an object with the `id` and `sub` properties and push it
// to the `a` array
a.push({
id: i,
// The `sub` property's value is generated recursively
sub: f(t, i)
});
}
}
// Finish by returning the `a` array
return a;
}
// Print the outputted array in a pretty way
// We call the `f` function with the 0 parameter because 0 is the parent of the
// nodes that should be directly put in the returned array
alert(JSON.stringify(f(t, 0)));
On Node.js 0.12.13 running this code instead of the alert at the end of the above snippet:
var util = require('util');
console.log(util.inspect(f(t, 0), {
colors: true,
depth: null
}));
prints the following:
[ { id: 1,
sub:
[ { id: 3, sub: [ { id: 30, sub: [] }, { id: 31, sub: [] } ] },
{ id: 4, sub: [] } ] },
{ id: 2,
sub:
[ { id: 5, sub: [] },
{ id: 6, sub: [] },
{ id: 7, sub: [ { id: 70, sub: [] }, { id: 71, sub: [] } ] } ] } ]
which I think is what you want.
I also read this page where another solution, possibly more efficient, is described.