Question

I want to save changes made to my document. The easiest way to do this is to store the actual changes made to a document. What I mean:

var changes = {
  $set: {
    text: 'Some text.'
  }
}

db.posts.update({
  _id: _id
}, changes)

db.changes.insert({
  postid: _id,
  changes: changes
})

However I’m getting the error (with good reason):

Error: key $set must not start with '$'

What’s the easiest way to store changes?

Or perhaps I’m approaching the problem wrong and you have a better solution. I want users to be able to see a log of changes people make to any post or, in fact, anything. I’m not going to make a function for every time of change. Editing the text is just one of many ways to make changes to a document.

Answer 1

This is a limitation within MongoDB. There are certain reserved characters one of them being $ due to how querying must work. When using operators there would be ambiguity between the document in the collection and the document used for updating.

I would recommend stripping out the $ symbols. I would instead use these words in place of the operators you are trying to use:

• CREATE
• SET
• DELETE