Aggregate constructor used for building aggregation pipelines. Do not instantiate this class directly, use Model.aggregate() instead.

Example:

const aggregate = Model.aggregate([
  { $project: { a: 1, b: 1 } },
  { $skip: 5 }
]);

Model.
  aggregate([{ $match: { age: { $gte: 21 }}}]).
  unwind('tags').
  exec(callback);

Note:

• The documents returned are plain javascript objects, not mongoose documents (since any shape of document can be returned).
• Mongoose does not cast pipeline stages. The below will not work unless _id is a string in the database

  new Aggregate([{ $match: { _id: '00000000000000000000000a' } }]);
  // Do this instead to cast to an ObjectId
  new Aggregate([{ $match: { _id: mongoose.Types.ObjectId('00000000000000000000000a') } }]);

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

const agg = Model.aggregate([{ $match: { age: { $gte: 25 } } }]);
for await (const doc of agg) {
  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.

Sets an option on this aggregation. This function will be deprecated in a future release. Use the cursor(), collation(), etc. helpers to set individual options, or access agg.options directly.

Note that MongoDB aggregations do not support the noCursorTimeout flag, if you try setting that flag with this function you will get a "unrecognized field 'noCursorTimeout'" error.

Appends a new $addFields operator to this aggregate pipeline. Requires MongoDB v3.4+ to work

Examples:

// adding new fields based on existing fields
aggregate.addFields({
    newField: '$b.nested'
  , plusTen: { $add: ['$val', 10]}
  , sub: {
       name: '$a'
    }
})

// etc
aggregate.addFields({ salary_k: { $divide: [ "$salary", 1000 ] } });

Sets the allowDiskUse option for the aggregation query (ignored for < 2.6.0)

Example:

await Model.aggregate([{ $match: { foo: 'bar' } }]).allowDiskUse(true);

Appends new operators to this aggregate pipeline

Examples:

aggregate.append({ $project: { field: 1 }}, { $limit: 2 });

// or pass an array
var pipeline = [{ $match: { daw: 'Logic Audio X' }} ];
aggregate.append(pipeline);

Executes the query returning a Promise which will be resolved with either the doc(s) or rejected with the error. Like .then(), but only takes a rejection handler.

Adds a collation

Example:

Model.aggregate(..).collation({ locale: 'en_US', strength: 1 }).exec();

Appends a new $count operator to this aggregate pipeline.

Examples:

aggregate.count("userCount");

Sets the cursor option option for the aggregation query (ignored for < 2.6.0). Note the different syntax below: .exec() returns a cursor object, and no callback is necessary.

Example:

var cursor = Model.aggregate(..).cursor({ batchSize: 1000 }).exec();
cursor.eachAsync(function(error, doc) {
  // use doc
});

Executes the aggregate pipeline on the currently bound Model.

Example:

aggregate.exec(callback);

// Because a promise is returned, the `callback` is optional.
var promise = aggregate.exec();
promise.then(..);

Execute the aggregation with explain

Example:

Model.aggregate(..).explain(callback)

Combines multiple aggregation pipelines.

Example:

Model.aggregate(...)
 .facet({
   books: [{ groupBy: '$author' }],
   price: [{ $bucketAuto: { groupBy: '$price', buckets: 2 } }]
 })
 .exec();

// Output: { books: [...], price: [{...}, {...}] }

Appends new custom $graphLookup operator(s) to this aggregate pipeline, performing a recursive search on a collection.

Note that graphLookup can only consume at most 100MB of memory, and does not allow disk use even if { allowDiskUse: true } is specified.

Examples:

// Suppose we have a collection of courses, where a document might look like `{ _id: 0, name: 'Calculus', prerequisite: 'Trigonometry'}` and `{ _id: 0, name: 'Trigonometry', prerequisite: 'Algebra' }`
 aggregate.graphLookup({ from: 'courses', startWith: '$prerequisite', connectFromField: 'prerequisite', connectToField: 'name', as: 'prerequisites', maxDepth: 3 }) // this will recursively search the 'courses' collection up to 3 prerequisites

Appends a new custom $group operator to this aggregate pipeline.

Examples:

aggregate.group({ _id: "$department" });

Sets the hint option for the aggregation query (ignored for < 3.6.0)

Example:

Model.aggregate(..).hint({ qty: 1, category: 1 }).exec(callback)

Appends a new $limit operator to this aggregate pipeline.

Examples:

aggregate.limit(10);

Appends new custom $lookup operator(s) to this aggregate pipeline.

Examples:

aggregate.lookup({ from: 'users', localField: 'userId', foreignField: '_id', as: 'users' });

Appends a new custom $match operator to this aggregate pipeline.

Examples:

aggregate.match({ department: { $in: [ "sales", "engineering" ] } });

Get/set the model that this aggregation will execute on.

Example:

const aggregate = MyModel.aggregate([{ $match: { answer: 42 } }]);
aggregate.model() === MyModel; // true

// Change the model. There's rarely any reason to do this.
aggregate.model(SomeOtherModel);
aggregate.model() === SomeOtherModel; // true

Appends a new $geoNear operator to this aggregate pipeline.

NOTE:

MUST be used as the first operator in the pipeline.

Examples:

aggregate.near({
  near: [40.724, -73.997],
  distanceField: "dist.calculated", // required
  maxDistance: 0.008,
  query: { type: "public" },
  includeLocs: "dist.location",
  uniqueDocs: true,
  num: 5
});

Lets you set arbitrary options, for middleware or plugins.

Example:

var agg = Model.aggregate(..).option({ allowDiskUse: true }); // Set the `allowDiskUse` option
agg.options; // `{ allowDiskUse: true }`

Contains options passed down to the aggregate command.

Supported options are

• readPreference
• cursor
• explain
• allowDiskUse
• maxTimeMS
• bypassDocumentValidation
• raw
• promoteLongs
• promoteValues
• promoteBuffers
• collation
• comment
• session

Returns the current pipeline

Example:

MyModel.aggregate().match({ test: 1 }).pipeline(); // [{ $match: { test: 1 } }]

Appends a new $project operator to this aggregate pipeline.

Mongoose query selection syntax is also supported.

Examples:

// include a, include b, exclude _id
aggregate.project("a b -_id");

// or you may use object notation, useful when
// you have keys already prefixed with a "-"
aggregate.project({a: 1, b: 1, _id: 0});

// reshaping documents
aggregate.project({
    newField: '$b.nested'
  , plusTen: { $add: ['$val', 10]}
  , sub: {
       name: '$a'
    }
})

// etc
aggregate.project({ salary_k: { $divide: [ "$salary", 1000 ] } });

Sets the readPreference option for the aggregation query.

Example:

Model.aggregate(..).read('primaryPreferred').exec(callback)

Sets the readConcern level for the aggregation query.

Example:

Model.aggregate(..).readConcern('majority').exec(callback)

Appends a new $redact operator to this aggregate pipeline.

If 3 arguments are supplied, Mongoose will wrap them with if-then-else of $cond operator respectively If thenExpr or elseExpr is string, make sure it starts with $$, like $$DESCEND, $$PRUNE or $$KEEP.

Example:

Model.aggregate(...)
 .redact({
   $cond: {
     if: { $eq: [ '$level', 5 ] },
     then: '$$PRUNE',
     else: '$$DESCEND'
   }
 })
 .exec();

// $redact often comes with $cond operator, you can also use the following syntax provided by mongoose
Model.aggregate(...)
 .redact({ $eq: [ '$level', 5 ] }, '$$PRUNE', '$$DESCEND')
 .exec();

Appends a new $replaceRoot operator to this aggregate pipeline.

Note that the $replaceRoot operator requires field strings to start with '$'. If you are passing in a string Mongoose will prepend '$' if the specified field doesn't start '$'. If you are passing in an object the strings in your expression will not be altered.

Examples:

aggregate.replaceRoot("user");

aggregate.replaceRoot({ x: { $concat: ['$this', '$that'] } });

Appends new custom $sample operator(s) to this aggregate pipeline.

Examples:

aggregate.sample(3); // Add a pipeline that picks 3 random documents

Sets the session for this aggregation. Useful for transactions.

Example:

const session = await Model.startSession();
await Model.aggregate(..).session(session);

Appends a new $skip operator to this aggregate pipeline.

Examples:

aggregate.skip(10);

Appends a new $sort operator to this aggregate pipeline.

If an object is passed, values allowed are asc, desc, ascending, descending, 1, and -1.

If a string is passed, it must be a space delimited list of path names. The sort order of each path is ascending unless the path name is prefixed with - which will be treated as descending.

Examples:

// these are equivalent
aggregate.sort({ field: 'asc', test: -1 });
aggregate.sort('field -test');

Appends a new $sortByCount operator to this aggregate pipeline. Accepts either a string field name or a pipeline object.

Note that the $sortByCount operator requires the new root to start with '$'. Mongoose will prepend '$' if the specified field name doesn't start with '$'.

Examples:

aggregate.sortByCount('users');
aggregate.sortByCount({ $mergeObjects: [ "$employee", "$business" ] })

Provides promise for aggregate.

Example:

Model.aggregate(..).then(successCallback, errorCallback);

Appends new custom $unwind operator(s) to this aggregate pipeline.

Note that the $unwind operator requires the path name to start with '$'. Mongoose will prepend '$' if the specified field doesn't start '$'.

Examples:

aggregate.unwind("tags");
aggregate.unwind("a", "b", "c");