Ok there are a couple of things going on here..I have two collections: test and test1. The documents in both collections have an array field (tags and tags1, respectively) that contains some tags. I need to find the intersection of these tags and also fetch the whole document from collection test1 if even a single tag matches.
> db.test.find();
{
"_id" : ObjectId("5166c19b32d001b79b32c72a"),
"tags" : [
"a",
"b",
"c"
]
}
> db.test1.find();
{
"_id" : ObjectId("5166c1c532d001b79b32c72b"),
"tags1" : [
"a",
"b",
"x",
"y"
]
}
> db.test.find().forEach(function(doc){db.test1.find({tags1:{$in:doc.tags}})});
Surprisingly this doesn't return anything. However when I try it with a single document, it works:
> var doc = db.test.findOne();
> db.test1.find({tags1:{$in:doc.tags}});
{ "_id" : ObjectId("5166c1c532d001b79b32c72b"), "tags1" : [ "a", "b", "x", "y" ] }
But this is part of what I need. I need intersection as well. So I tried this:
> db.test1.find({tags1:{$in:doc.tags}},{"tags1.$":1});
{ "_id" : ObjectId("5166c1c532d001b79b32c72b"), "tags1" : [ "a" ] }
But it returned just "a" whereas "a" and "b" both were in tags1. Does positional operator return just the first match? Also, using $in
won't exactly give me an intersection..How can I get an intersection (should return "a" and "b") irrespective of which array is compared against the other.
Now say there's an operator that can do this..
> db.test1.find({tags1:{$intersection:doc.tags}},{"tags1.$":1});
{ "_id" : ObjectId("5166c1c532d001b79b32c72b"), "tags1" : [ "a", "b" ] }
My requirement is, I need the entire tags1 array PLUS this intersection, in the same query like this:
> db.test1.find({tags1:{$intersection:doc.tags}},{"tags1":1, "tags1.$":1});
{ "_id" : ObjectId("5166c1c532d001b79b32c72b"), "tags1": [ "a", "b", "x", "y" ],
"tags1" : [ "a", "b" ] }
But this is an invalid json. Is renaming key possible, or this is possible only through aggregation framework (and across different collections?)? I tried the above query with $in
. But it behaved as if it totally ignored "tags:1"
projection.
PS: I am going to have at least 10k docs in test1 and very few (<10) in test. And this query is in real-time, so I want to avoid mapreduce :)
Thanks for any help!