AggregationCursor
AggregationCursor()
AggregationCursor.prototype.addCursorFlag()
AggregationCursor.prototype.close()
AggregationCursor.prototype.eachAsync()
AggregationCursor.prototype.map()
AggregationCursor.prototype.next()
AggregationCursor.prototype[Symbol.asyncIterator]()
AggregationCursor()
Parameters:
agg
«Aggregate»
Inherits:
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.
AggregationCursor.prototype.addCursorFlag()
Parameters:
flag
«String»value
«Boolean»
Returns:
- «AggregationCursor» this
Adds a cursor flag.
Useful for setting the noCursorTimeout
and tailable
flags.
AggregationCursor.prototype.close()
Parameters:
callback
«Function»
Returns:
- «Promise»
See:
Marks this cursor as closed. Will stop streaming and subsequent calls to
next()
will error.
AggregationCursor.prototype.eachAsync()
Parameters:
fn
«Function»[options]
«Object»[options.parallel]
«Number» the number of promises to execute in parallel. Defaults to 1.[callback]
«Function» executed when all docs have been processed
Returns:
- «Promise»
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.
AggregationCursor.prototype.map()
Parameters:
fn
«Function»
Returns:
- «AggregationCursor»
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);
});
AggregationCursor.prototype.next()
Parameters:
callback
«Function»
Returns:
- «Promise»
Get the next document from this cursor. Will return null
when there are
no documents left.
AggregationCursor.prototype[Symbol.asyncIterator]()
Returns an asyncIterator for use with for/await/of
loops
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.