Mongo query in Object of arrays - ruby-on-rails

Question

Document example
{
"_id": 1,
"test": {
"item_obj": {
"item1": ["a", "b"],
"item2": ["c"],
"item3": ["a", "d"]
}
}
}
I want to fetch documents where "a" exists in test.item_obj. "a" may exist in any array. And we don't know the keys present inside item_obj (No idea item1, item2 or item3 exists).
Need rails-mongo query.

Answer 1

If this is your search case, then whatever way you look at it you need the JavaScript evaluation of the $where clause to resolve your current structure. In the shell example ( since you need to use the JavaScript expression anyway ):
db.collection.find(function() {
var root = this.test.item_obj;
return Object.keys(root).some(function(key) {
return root[key] == "a";
});
})
Or for mongoid that is something like:
func = <<-eof
var root = this.test.item_obj;
return Object.keys(root).some(function(key) {
return root[key] == "a";
});
eof
Model.for_js(func)
However, if you simply change your structure to define "items_objects" as an array as follows:
{
"_id": 1,
"test": {
"item_objects": [
{ "name": "item1", "data": ["a","b"] },
{ "name": "item2", "data": ["c"] },
{ "name": "item3", "data": ["a","d"] }
}
}
}
Then asking for what you want here is as basic as:
db.collection.find({
"test.item_objects.data": "a"
})
Or for mongoid:
Model.where( "test.item_objects.data" => "a" )
Nested arrays are not really a great idea though, so perhaps live with:
{
"_id": 1,
"test": {
"item_objects": [
{ "name": "item1", "data": "a" },
{ "name": "item1", "data": "b" },
{ "name": "item2", "data": "c" },
{ "name": "item3", "data": "a" },
{ "name": "item3", "data": "d" }
}
}
}
Which is basically the same thing, but a but more long winded. But ultimately much more easy to deal with in atomic updates. And of course the query to find the values in the document is exactly the same.