More complex update operations

We already learned how to add attributes or change the value of attributes in existing documents:

collection.update( 
  {'n': /^#1/}, 
  {'$set': {'v': 5} }, 
  {'multi': true}, 
  function (err, count) { 
    // ... 
  }

This would set the value of the v attribute to 5 for all documents whose n value starts with #1.

This is probably the most regularly used update operation. Some other ways to update documents are available, however. Numeric attributes can be increased, for example:

collection.update(
  {'n': /^#1/},
  {'$inc': {'v': +1} },
  {'multi': true},
  function (err, count) {
    // ...
  }

There is no $dec operation, but of course, we can increase by -1:

collection.update(
  {'n': /^#1/},
  {'$inc': {'v': -1} },
  {'multi': true},
  function (err, count) {
    // ...
  }

Multiplication is possible, too:

collection.update(
  {'n': /^#1/},
  {'$mul': {'v': 2} },
  {'multi': true},
  function (err, count) {
    // ...
  }

There are several other operators:

• $rename...