Question

I’ve read the blog post on ES regarding versioning.

However, I’d like to be able to get the previous _source documents from an update.

For example, let’s say I have this object:

{
    "name": "John",
    "age": 32,
    "job": "janitorial technician"
}
// this becomes version 1

And I update it to:

{
    "name": "John",
    "age": 32,
    "job": "president"
}
// this becomes version 2

Then, through versioning in ES, would I be able to get the previous job property of the object? I’ve tried this:

curl -XGET "localhost:9200/index/type/id?version=1"

but that just returns the most up-to-date _source object (the one where John is president).

I’d actually like to implement a version differences aspect much like StackOverflow does. (BTW, I’m using elastic-search as my main db – if there’s a way to do this with other NoSQL databases, I’d be happy to try it out. Preferably, one that integrates well with ES.)

Answer 1

No, you can’t do this using the builtin versioning. All that does is to store the current version number to prevent you applying updates out of order.

If you wanted to keep multiple versions available, then you’d have to implement that yourself. Depending on how many versions you are likely to want to store, you could take three approaches:

For low volume changes:

1) store older versions within the same document

{ text: "foo bar",
  date:  "2011-11-01",
  previous: [
      { date: '2011-10-01', content: { text: 'Foo Bar' }},
      { date: '2011-09-01', content: { text: 'Foo-bar!' }},
  ]
}

For high volume changes:

2) add a current flag:

{
   doc_id:  123,
   version: 3,
   text:    "foo bar",
   date:    "2011-11-01",
   current: true
}

{
   doc_id:  123,
   version: 2,
   text:    "Foo Bar",
   date:    "2011-10-01",
   current: false
}

3) Same as (2) above, but store the old versions in a separate index, so keeping your “live” index, which will be used for the majority of your queries, small and more performant.