Question

So, I need to write something in Rails 3 that does a query to a MongoDB (If you don’t know mongo I don’t need the code just some ideas) that can query the data for close matches. For instance, let us say you are searching a collection for {item : a, item2 : b, item3 : c}. And exact match would have all three, but I also want matches that omit one of the three keys. I have two theories on how I should handle this. One would be to do multiple queries to omit certain parts of the data and the other would be to write a complex or statement. I don’t feel these are the best solutions though. Could anyone else suggest something to me? Even if it is from an SQL perspective, that would work for me.

I do need something that can be done fast. This is for a search that needs to return results as fast as possible.

Answer 1

Yet another approach would be to use MapReduce.

With it you can calculate how many fields a document matches.

Though it’s not very performant approach at the moment (but one of the most flexible).

The code can be something like this:

var m = function() {
  var fieldsToMatch = {item: a, item2: b, item3: c};
  for(var k in fieldsToMatch) {
    if(this[k] == fieldsToMatch[k]) {
      emit(this.id, {count : 1}); // emit 1 for each field matched 
    }
  }
};

var r = function(k, vals) {
  var result = {count: 0};
  vals.forEach(function(v) {
    result.count += v.count;
  });
  return result;
}

db.items.mapReduce(m, r, {out: 'out_collection'});