Search on multiple collections in MongoDB

Question

I know the theory of MongoDB and the fact that is doesn\'t support joins, and that I should use embeded documents or denormalize as much as possible, but here goes:

Answer 1

Based on @brian-moquin and others, I made a set of functions to search entire collections with entire keys(fields) by simple keyword.

It's in my gist; https://gist.github.com/fkiller/005dc8a07eaa3321110b3e5753dda71b

For more detail, I first made a function to gather all keys.

function keys(collectionName) {
    mr = db.runCommand({
        'mapreduce': collectionName,
        'map': function () {
            for (var key in this) { emit(key, null); }
        },
        'reduce': function (key, stuff) { return null; },
        'out': 'my_collection' + '_keys'
    });
    return db[mr.result].distinct('_id');
}

Then one more to generate $or query from keys array.

function createOR(fieldNames, keyword) {
    var query = [];
    fieldNames.forEach(function (item) {
        var temp = {};
        temp[item] = { $regex: '.*' + keyword + '.*' };
        query.push(temp);
    });
    if (query.length == 0) return false;
    return { $or: query };
}

Below is a function to search a single collection.

function findany(collection, keyword) {
    var query = createOR(keys(collection.getName()));
    if (query) {
        return collection.findOne(query, keyword);
    } else {
        return false;
    }
}

And, finally a search function for every collections.

function searchAll(keyword) {
    var all = db.getCollectionNames();
    var results = [];
    all.forEach(function (collectionName) {
        print(collectionName);
        if (db[collectionName]) results.push(findany(db[collectionName], keyword));
    });
    return results;
}

You can simply load all functions in Mongo console, and execute searchAll('any keyword')