How to update MongoDB document based on its previous values?

Question

Sorry if this is pretty basic, but I'm a mongodb newbie and haven't been able to find an answer to this:

Let's say I'm doing the following:

db.collection("bugs").updateOne({ _id: searchId }, { $set: { "fixed": true }}

How to set "fixed" to the contrary of whatever the last value of "fixed" was? Without any additional queries? Something like { $set: { "fixed": !fixed }}

Answer 1

It is not really possible to achieve this in MongoDB as of now in just one operation by sticking to the idea of storing boolean values (might be possible in future versions of MongoDB). But, there is a workaround to do this by storing bits (0 or 1) to represent true or false instead of boolean values and performing bitwise xor operation on those in MongoDB as follows:

db.collection("bugs").updateOne(
  {
    _id: searchId
  },
  { 
    $bit : {
     fixed: {
       xor: NumberInt(1)
     }
    }
  }
)

Please note that you also have to store 0 as NumberInt(0) to represent false and 1 as NumberInt(1) to represent true in the fixed prop as MongoDB by default treats all numbers as floating-point values.

Answer 2

This is not possible in MongoDB. You have to retrieve the doc from the db and then update it:

var doc = db.collection("bugs").findOne({ _id: searchId });
db.collection("bugs").updateOne({ _id: searchId }, { $set: { "fixed": !doc.fixed } }