AggregationCursor

An AggregationCursor is a concurrency primitive for processing aggregation results one document at a time. It is analogous to QueryCursor.

An AggregationCursor fulfills the Node.js streams3 API, in addition to several other mechanisms for loading documents from MongoDB one at a time.

Creating an AggregationCursor executes the model's pre aggregate hooks, but not the model's post aggregate hooks.

Unless you're an advanced user, do not instantiate this class directly. Use Aggregate#cursor() instead.

Returns an asyncIterator for use with [for/await/of loops](https://thecodebarbarian.com/getting-started-with-async-iterators-in-node-js You do not need to call this function explicitly, the JavaScript runtime will call it for you.

Example

// Async iterator without explicitly calling `cursor()`. Mongoose still
// creates an AggregationCursor instance internally.
const agg = Model.aggregate([{ $match: { age: { $gte: 25 } } }]);
for await (const doc of agg) {
  console.log(doc.name);
}

// You can also use an AggregationCursor instance for async iteration
const cursor = Model.aggregate([{ $match: { age: { $gte: 25 } } }]).cursor();
for await (const doc of cursor) {
  console.log(doc.name);
}

Node.js 10.x supports async iterators natively without any flags. You can enable async iterators in Node.js 8.x using the --harmony_async_iteration flag.

Note: This function is not set if Symbol.asyncIterator is undefined. If Symbol.asyncIterator is undefined, that means your Node.js version does not support async iterators.

Adds a cursor flag. Useful for setting the noCursorTimeout and tailable flags.

Marks this cursor as closed. Will stop streaming and subsequent calls to next() will error.

Execute fn for every document in the cursor. If fn returns a promise, will wait for the promise to resolve before iterating on to the next one. Returns a promise that resolves when done.

Registers a transform function which subsequently maps documents retrieved via the streams interface or .next()

Example

// Map documents returned by `data` events
Thing.
  find({ name: /^hello/ }).
  cursor().
  map(function (doc) {
   doc.foo = "bar";
   return doc;
  })
  on('data', function(doc) { console.log(doc.foo); });

// Or map documents returned by `.next()`
const cursor = Thing.find({ name: /^hello/ }).
  cursor().
  map(function (doc) {
    doc.foo = "bar";
    return doc;
  });
cursor.next(function(error, doc) {
  console.log(doc.foo);
});

Get the next document from this cursor. Will return null when there are no documents left.