Question

I wonder how it would be possible to implement a positional inverted index in MongoDB. By using the multikey feature an inverted index can be created, but how would it be possible to in a efficient way be able to store the positions of the occurences as well?

Let’s say we have this object

obj = {
  name: "Apollo",
  text: "Some text about Apollo moon landings",
  keywords: [ "some", "text", "about", "apollo", "moon", "landings" ]
}

I would know like to be able to make a query where “apollo” and “landings” would have to be connected, and not just make an “intersection” query.

Answer 1

What about an object like:

obj = {
  name: "Apollo",
  text: "Some text about Apollo moon landings",
  keywords: [
    {idx:0, text: "some"},
    {idx:1, text: "text"}, 
    {idx:2, text: "about"}, 
    {idx:3, text: "apollo"}, 
    {idx:4, text: "moon"}, 
    {idx:5, text: "landings"}
  ]
}

You can do an ensureIndex on “keywords.text” to do a query where both keywords exists and then use javascript in a “where” filter to check relative positions of the input keywords.