MongoDB/NoSQL: Keeping Document Change History

Question

A fairly common requirement in database applications is to track changes to one or more specific entities in a database. I\'ve heard this called row versioning, a log table

Answer 1

Why not a variation on Store changes within the document ?

Instead of storing versions against each key pair, the current key pairs in the document always represents the most recent state and a 'log' of changes is stored within a history array. Only those keys which have changed since creation will have an entry in the log.

{
  _id: "4c6b9456f61f000000007ba6"
  title: "Bar",
  body: "Is this thing on?",
  tags: [ "test", "trivial" ],
  comments: [
    { key: 1, author: "joe", body: "Something cool" },
    { key: 2, author: "xxx", body: "Spam", deleted: true },
    { key: 3, author: "jim", body: "Not bad at all" }
  ],
  history: [
    { 
      who: "joe",
      when: 20160101,
      what: { title: "Foo", body: "What should I write?" }
    },
    { 
      who: "jim",
      when: 20160105,
      what: { tags: ["test", "test2"], comments: { key: 3, body: "Not baaad at all" }
    }
  ]
}