Model

A Model is a class that's your primary tool for interacting with MongoDB. An instance of a Model is called a Document.

In Mongoose, the term "Model" refers to subclasses of the mongoose.Model class. You should not use the mongoose.Model class directly. The mongoose.model() and connection.model() functions create subclasses of mongoose.Model as shown below.

Example:

// `UserModel` is a "Model", a subclass of `mongoose.Model`.
const UserModel = mongoose.model('User', new Schema({ name: String }));

// You can use a Model to create new documents using `new`:
const userDoc = new UserModel({ name: 'Foo' });
await userDoc.save();

// You also use a model to create queries:
const userFromDb = await UserModel.findOne({ name: 'Foo' });

Performs aggregations on the models collection.

If a callback is passed, the aggregate is executed and a Promise is returned. If a callback is not passed, the aggregate itself is returned.

This function triggers the following middleware.

• aggregate()

Example:

// Find the max balance of all accounts
Users.aggregate([
  { $group: { _id: null, maxBalance: { $max: '$balance' }}},
  { $project: { _id: 0, maxBalance: 1 }}
]).
then(function (res) {
  console.log(res); // [ { maxBalance: 98000 } ]
});

// Or use the aggregation pipeline builder.
Users.aggregate().
  group({ _id: null, maxBalance: { $max: '$balance' } }).
  project('-id maxBalance').
  exec(function (err, res) {
    if (err) return handleError(err);
    console.log(res); // [ { maxBalance: 98 } ]
  });

NOTE:

• Mongoose does not cast aggregation pipelines to the model's schema because $project and $group operators allow redefining the "shape" of the documents at any stage of the pipeline, which may leave documents in an incompatible format. You can use the mongoose-cast-aggregation plugin to enable minimal casting for aggregation pipelines.
• The documents returned are plain javascript objects, not mongoose documents (since any shape of document can be returned).

More About Aggregations:

• Mongoose Aggregate
• An Introduction to Mongoose Aggregate
• MongoDB Aggregation docs

Sends multiple insertOne, updateOne, updateMany, replaceOne, deleteOne, and/or deleteMany operations to the MongoDB server in one command. This is faster than sending multiple independent operations (e.g. if you use create()) because with bulkWrite() there is only one round trip to MongoDB.

Mongoose will perform casting on all operations you provide.

This function does not trigger any middleware, neither save(), nor update(). If you need to trigger save() middleware for every document use create() instead.

Example:

Character.bulkWrite([
  {
    insertOne: {
      document: {
        name: 'Eddard Stark',
        title: 'Warden of the North'
      }
    }
  },
  {
    updateOne: {
      filter: { name: 'Eddard Stark' },
      // If you were using the MongoDB driver directly, you'd need to do
      // `update: { $set: { title: ... } }` but mongoose adds $set for
      // you.
      update: { title: 'Hand of the King' }
    }
  },
  {
    deleteOne: {
      {
        filter: { name: 'Eddard Stark' }
      }
    }
  }
]).then(res => {
 // Prints "1 1 1"
 console.log(res.insertedCount, res.modifiedCount, res.deletedCount);
});

The supported operations are:

• insertOne
• updateOne
• updateMany
• deleteOne
• deleteMany
• replaceOne

Deletes all indexes that aren't defined in this model's schema. Used by syncIndexes().

The returned promise resolves to a list of the dropped indexes' names as an array

Counts number of documents that match filter in a database collection.

This method is deprecated. If you want to count the number of documents in a collection, e.g. count({}), use the estimatedDocumentCount() function instead. Otherwise, use the countDocuments() function instead.

Example:

Adventure.count({ type: 'jungle' }, function (err, count) {
  if (err) ..
  console.log('there are %d jungle adventures', count);
});

Counts number of documents matching filter in a database collection.

Example:

Adventure.countDocuments({ type: 'jungle' }, function (err, count) {
  console.log('there are %d jungle adventures', count);
});

If you want to count all documents in a large collection, use the estimatedDocumentCount() function instead. If you call countDocuments({}), MongoDB will always execute a full collection scan and not use any indexes.

The countDocuments() function is similar to count(), but there are a few operators that countDocuments() does not support. Below are the operators that count() supports but countDocuments() does not, and the suggested replacement:

• $where: $expr
• $near: $geoWithin with $center
• $nearSphere: $geoWithin with $centerSphere

Shortcut for saving one or more documents to the database. MyModel.create(docs) does new MyModel(doc).save() for every doc in docs.

This function triggers the following middleware.

• save()

Example:

// Insert one new `Character` document
await Character.create({ name: 'Jean-Luc Picard' });

// Insert multiple new `Character` documents
await Character.create([{ name: 'Will Riker' }, { name: 'Geordi LaForge' }]);

// Create a new character within a transaction. Note that you **must**
// pass an array as the first parameter to `create()` if you want to
// specify options.
await Character.create([{ name: 'Jean-Luc Picard' }], { session });

Create the collection for this model. By default, if no indexes are specified, mongoose will not create the collection for the model until any documents are created. Use this method to create the collection explicitly.

Note 1: You may need to call this before starting a transaction See https://docs.mongodb.com/manual/core/transactions/#transactions-and-operations

Note 2: You don't have to call this if your schema contains index or unique field. In that case, just use Model.init()

Example:

const userSchema = new Schema({ name: String })
const User = mongoose.model('User', userSchema);

User.createCollection().then(function(collection) {
  console.log('Collection is created!');
});

Similar to ensureIndexes(), except for it uses the createIndex function.

Deletes all of the documents that match conditions from the collection. Behaves like remove(), but deletes all documents that match conditions regardless of the single option.

Example:

await Character.deleteMany({ name: /Stark/, age: { $gte: 18 } });

Note:

This function triggers deleteMany query hooks. Read the middleware docs to learn more.

Deletes the first document that matches conditions from the collection. Behaves like remove(), but deletes at most one document regardless of the single option.

Example:

await Character.deleteOne({ name: 'Eddard Stark' });

Note:

This function triggers deleteOne query hooks. Read the middleware docs to learn more.

Adds a discriminator type.

Example:

function BaseSchema() {
  Schema.apply(this, arguments);

  this.add({
    name: String,
    createdAt: Date
  });
}
util.inherits(BaseSchema, Schema);

const PersonSchema = new BaseSchema();
const BossSchema = new BaseSchema({ department: String });

const Person = mongoose.model('Person', PersonSchema);
const Boss = Person.discriminator('Boss', BossSchema);
new Boss().__t; // "Boss". `__t` is the default `discriminatorKey`

const employeeSchema = new Schema({ boss: ObjectId });
const Employee = Person.discriminator('Employee', employeeSchema, 'staff');
new Employee().__t; // "staff" because of 3rd argument above

Creates a Query for a distinct operation.

Passing a callback executes the query.

Example

Link.distinct('url', { clicks: {$gt: 100}}, function (err, result) {
  if (err) return handleError(err);

  assert(Array.isArray(result));
  console.log('unique urls with more than 100 clicks', result);
})

const query = Link.distinct('url');
query.exec(callback);

Sends createIndex commands to mongo for each index declared in the schema. The createIndex commands are sent in series.

Example:

Event.ensureIndexes(function (err) {
  if (err) return handleError(err);
});

After completion, an index event is emitted on this Model passing an error if one occurred.

Example:

const eventSchema = new Schema({ thing: { type: 'string', unique: true }})
const Event = mongoose.model('Event', eventSchema);

Event.on('index', function (err) {
  if (err) console.error(err); // error occurred during index creation
})

NOTE: It is not recommended that you run this in production. Index creation may impact database performance depending on your load. Use with caution.

Estimates the number of documents in the MongoDB collection. Faster than using countDocuments() for large collections because estimatedDocumentCount() uses collection metadata rather than scanning the entire collection.

Example:

const numAdventures = Adventure.estimatedDocumentCount();

Event emitter that reports any errors that occurred. Useful for global error handling.

Example:

MyModel.events.on('error', err => console.log(err.message));

// Prints a 'CastError' because of the above handler
await MyModel.findOne({ _id: 'notanid' }).catch(noop);

Returns true if at least one document exists in the database that matches the given filter, and false otherwise.

Under the hood, MyModel.exists({ answer: 42 }) is equivalent to MyModel.findOne({ answer: 42 }).select({ _id: 1 }).lean().then(doc => !!doc)

Example:

await Character.deleteMany({});
await Character.create({ name: 'Jean-Luc Picard' });

await Character.exists({ name: /picard/i }); // true
await Character.exists({ name: /riker/i }); // false

This function triggers the following middleware.

• findOne()

Finds documents.

Mongoose casts the filter to match the model's schema before the command is sent. See our query casting tutorial for more information on how Mongoose casts filter.

Examples:

// find all documents
await MyModel.find({});

// find all documents named john and at least 18
await MyModel.find({ name: 'john', age: { $gte: 18 } }).exec();

// executes, passing results to callback
MyModel.find({ name: 'john', age: { $gte: 18 }}, function (err, docs) {});

// executes, name LIKE john and only selecting the "name" and "friends" fields
await MyModel.find({ name: /john/i }, 'name friends').exec();

// passing options
await MyModel.find({ name: /john/i }, null, { skip: 10 }).exec();

Finds a single document by its _id field. findById(id) is almost* equivalent to findOne({ _id: id }). If you want to query by a document's _id, use findById() instead of findOne().

The id is cast based on the Schema before sending the command.

This function triggers the following middleware.

• findOne()

* Except for how it treats undefined. If you use findOne(), you'll see that findOne(undefined) and findOne({ _id: undefined }) are equivalent to findOne({}) and return arbitrary documents. However, mongoose translates findById(undefined) into findOne({ _id: null }).

Example:

// Find the adventure with the given `id`, or `null` if not found
await Adventure.findById(id).exec();

// using callback
Adventure.findById(id, function (err, adventure) {});

// select only the adventures name and length
await Adventure.findById(id, 'name length').exec();

Issue a MongoDB findOneAndDelete() command by a document's _id field. In other words, findByIdAndDelete(id) is a shorthand for findOneAndDelete({ _id: id }).

This function triggers the following middleware.

• findOneAndDelete()

Issue a mongodb findAndModify remove command by a document's _id field. findByIdAndRemove(id, ...) is equivalent to findOneAndRemove({ _id: id }, ...).

Finds a matching document, removes it, passing the found document (if any) to the callback.

Executes the query if callback is passed.

This function triggers the following middleware.

• findOneAndRemove()

Options:

• sort: if multiple docs are found by the conditions, sets the sort order to choose which doc to update
• select: sets the document fields to return
• rawResult: if true, returns the raw result from the MongoDB driver
• strict: overwrites the schema's strict mode option for this update

Examples:

A.findByIdAndRemove(id, options, callback) // executes
A.findByIdAndRemove(id, options)  // return Query
A.findByIdAndRemove(id, callback) // executes
A.findByIdAndRemove(id) // returns Query
A.findByIdAndRemove()           // returns Query

Issues a mongodb findAndModify update command by a document's _id field. findByIdAndUpdate(id, ...) is equivalent to findOneAndUpdate({ _id: id }, ...).

Finds a matching document, updates it according to the update arg, passing any options, and returns the found document (if any) to the callback. The query executes if callback is passed.

This function triggers the following middleware.

• findOneAndUpdate()

Options:

• new: bool - true to return the modified document rather than the original. defaults to false
• upsert: bool - creates the object if it doesn't exist. defaults to false.
• runValidators: if true, runs update validators on this command. Update validators validate the update operation against the model's schema.
• setDefaultsOnInsert: if this and upsert are true, mongoose will apply the defaults specified in the model's schema if a new document is created. This option only works on MongoDB >= 2.4 because it relies on MongoDB's $setOnInsert operator.
• sort: if multiple docs are found by the conditions, sets the sort order to choose which doc to update
• select: sets the document fields to return
• rawResult: if true, returns the raw result from the MongoDB driver
• strict: overwrites the schema's strict mode option for this update

Examples:

A.findByIdAndUpdate(id, update, options, callback) // executes
A.findByIdAndUpdate(id, update, options)  // returns Query
A.findByIdAndUpdate(id, update, callback) // executes
A.findByIdAndUpdate(id, update)           // returns Query
A.findByIdAndUpdate()                     // returns Query

Note:

All top level update keys which are not atomic operation names are treated as set operations:

Example:

Model.findByIdAndUpdate(id, { name: 'jason bourne' }, options, callback)

// is sent as
Model.findByIdAndUpdate(id, { $set: { name: 'jason bourne' }}, options, callback)

This helps prevent accidentally overwriting your document with { name: 'jason bourne' }.

Note:

Values are cast to their appropriate types when using the findAndModify helpers. However, the below are not executed by default.

• defaults. Use the setDefaultsOnInsert option to override.

findAndModify helpers support limited validation. You can enable these by setting the runValidators options, respectively.

If you need full-fledged validation, use the traditional approach of first retrieving the document.

Model.findById(id, function (err, doc) {
  if (err) ..
  doc.name = 'jason bourne';
  doc.save(callback);
});

Finds one document.

The conditions are cast to their respective SchemaTypes before the command is sent.

Note: conditions is optional, and if conditions is null or undefined, mongoose will send an empty findOne command to MongoDB, which will return an arbitrary document. If you're querying by _id, use findById() instead.

Example:

// Find one adventure whose `country` is 'Croatia', otherwise `null`
await Adventure.findOne({ country: 'Croatia' }).exec();

// using callback
Adventure.findOne({ country: 'Croatia' }, function (err, adventure) {});

// select only the adventures name and length
await Adventure.findOne({ country: 'Croatia' }, 'name length').exec();

Issue a MongoDB findOneAndDelete() command.

Finds a matching document, removes it, and passes the found document (if any) to the callback.

Executes the query if callback is passed.

This function triggers the following middleware.

• findOneAndDelete()

This function differs slightly from Model.findOneAndRemove() in that findOneAndRemove() becomes a MongoDB findAndModify() command, as opposed to a findOneAndDelete() command. For most mongoose use cases, this distinction is purely pedantic. You should use findOneAndDelete() unless you have a good reason not to.

Options:

• sort: if multiple docs are found by the conditions, sets the sort order to choose which doc to update
• maxTimeMS: puts a time limit on the query - requires mongodb >= 2.6.0
• select: sets the document fields to return, ex. { projection: { _id: 0 } }
• projection: equivalent to select
• rawResult: if true, returns the raw result from the MongoDB driver
• strict: overwrites the schema's strict mode option for this update

Examples:

A.findOneAndDelete(conditions, options, callback) // executes
A.findOneAndDelete(conditions, options)  // return Query
A.findOneAndDelete(conditions, callback) // executes
A.findOneAndDelete(conditions) // returns Query
A.findOneAndDelete()           // returns Query

Values are cast to their appropriate types when using the findAndModify helpers. However, the below are not executed by default.

• defaults. Use the setDefaultsOnInsert option to override.

findAndModify helpers support limited validation. You can enable these by setting the runValidators options, respectively.

If you need full-fledged validation, use the traditional approach of first retrieving the document.

Model.findById(id, function (err, doc) {
  if (err) ..
  doc.name = 'jason bourne';
  doc.save(callback);
});

Issue a mongodb findAndModify remove command.

Finds a matching document, removes it, passing the found document (if any) to the callback.

Executes the query if callback is passed.

This function triggers the following middleware.

• findOneAndRemove()

Options:

• sort: if multiple docs are found by the conditions, sets the sort order to choose which doc to update
• maxTimeMS: puts a time limit on the query - requires mongodb >= 2.6.0
• select: sets the document fields to return
• projection: like select, it determines which fields to return, ex. { projection: { _id: 0 } }
• rawResult: if true, returns the raw result from the MongoDB driver
• strict: overwrites the schema's strict mode option for this update

Examples:

A.findOneAndRemove(conditions, options, callback) // executes
A.findOneAndRemove(conditions, options)  // return Query
A.findOneAndRemove(conditions, callback) // executes
A.findOneAndRemove(conditions) // returns Query
A.findOneAndRemove()           // returns Query

Values are cast to their appropriate types when using the findAndModify helpers. However, the below are not executed by default.

• defaults. Use the setDefaultsOnInsert option to override.

findAndModify helpers support limited validation. You can enable these by setting the runValidators options, respectively.

If you need full-fledged validation, use the traditional approach of first retrieving the document.

Model.findById(id, function (err, doc) {
  if (err) ..
  doc.name = 'jason bourne';
  doc.save(callback);
});

Issue a MongoDB findOneAndReplace() command.

Finds a matching document, replaces it with the provided doc, and passes the returned doc to the callback.

Executes the query if callback is passed.

This function triggers the following query middleware.

• findOneAndReplace()

Options:

• sort: if multiple docs are found by the conditions, sets the sort order to choose which doc to update
• maxTimeMS: puts a time limit on the query - requires mongodb >= 2.6.0
• select: sets the document fields to return
• projection: like select, it determines which fields to return, ex. { projection: { _id: 0 } }
• rawResult: if true, returns the raw result from the MongoDB driver
• strict: overwrites the schema's strict mode option for this update

Examples:

A.findOneAndReplace(conditions, options, callback) // executes
A.findOneAndReplace(conditions, options)  // return Query
A.findOneAndReplace(conditions, callback) // executes
A.findOneAndReplace(conditions) // returns Query
A.findOneAndReplace()           // returns Query

Values are cast to their appropriate types when using the findAndModify helpers. However, the below are not executed by default.

• defaults. Use the setDefaultsOnInsert option to override.

Issues a mongodb findAndModify update command.

Finds a matching document, updates it according to the update arg, passing any options, and returns the found document (if any) to the callback. The query executes if callback is passed else a Query object is returned.

Options:

• new: bool - if true, return the modified document rather than the original. defaults to false (changed in 4.0)
• upsert: bool - creates the object if it doesn't exist. defaults to false.
• overwrite: bool - if true, replace the entire document.
• fields: {Object|String} - Field selection. Equivalent to .select(fields).findOneAndUpdate()
• maxTimeMS: puts a time limit on the query - requires mongodb >= 2.6.0
• sort: if multiple docs are found by the conditions, sets the sort order to choose which doc to update
• runValidators: if true, runs update validators on this command. Update validators validate the update operation against the model's schema.
• setDefaultsOnInsert: if this and upsert are true, mongoose will apply the defaults specified in the model's schema if a new document is created. This option only works on MongoDB >= 2.4 because it relies on MongoDB's $setOnInsert operator.
• rawResult: if true, returns the raw result from the MongoDB driver
• strict: overwrites the schema's strict mode option for this update

Examples:

A.findOneAndUpdate(conditions, update, options, callback) // executes
A.findOneAndUpdate(conditions, update, options)  // returns Query
A.findOneAndUpdate(conditions, update, callback) // executes
A.findOneAndUpdate(conditions, update)           // returns Query
A.findOneAndUpdate()                             // returns Query

Note:

All top level update keys which are not atomic operation names are treated as set operations:

Example:

const query = { name: 'borne' };
Model.findOneAndUpdate(query, { name: 'jason bourne' }, options, callback)

// is sent as
Model.findOneAndUpdate(query, { $set: { name: 'jason bourne' }}, options, callback)

This helps prevent accidentally overwriting your document with { name: 'jason bourne' }.

Note:

Values are cast to their appropriate types when using the findAndModify helpers. However, the below are not executed by default.

• defaults. Use the setDefaultsOnInsert option to override.

findAndModify helpers support limited validation. You can enable these by setting the runValidators options, respectively.

If you need full-fledged validation, use the traditional approach of first retrieving the document.

Model.findById(id, function (err, doc) {
  if (err) ..
  doc.name = 'jason bourne';
  doc.save(callback);
});

Implements $geoSearch functionality for Mongoose

This function does not trigger any middleware

Example:

const options = { near: [10, 10], maxDistance: 5 };
Locations.geoSearch({ type : "house" }, options, function(err, res) {
  console.log(res);
});

Options:

• near {Array} x,y point to search for
• maxDistance {Number} the maximum distance from the point near that a result can be
• limit {Number} The maximum number of results to return
• lean {Object|Boolean} return the raw object instead of the Mongoose Model

Shortcut for creating a new Document from existing raw data, pre-saved in the DB. The document returned has no paths marked as modified initially.

Example:

// hydrate previous data into a Mongoose document
const mongooseCandy = Candy.hydrate({ _id: '54108337212ffb6d459f854c', type: 'jelly bean' });

This function is responsible for building indexes, unless autoIndex is turned off.

Mongoose calls this function automatically when a model is created using mongoose.model() or connection.model(), so you don't need to call it. This function is also idempotent, so you may call it to get back a promise that will resolve when your indexes are finished building as an alternative to MyModel.on('index')

Example:

const eventSchema = new Schema({ thing: { type: 'string', unique: true }})
// This calls `Event.init()` implicitly, so you don't need to call
// `Event.init()` on your own.
const Event = mongoose.model('Event', eventSchema);

Event.init().then(function(Event) {
  // You can also use `Event.on('index')` if you prefer event emitters
  // over promises.
  console.log('Indexes are done building!');
});

Shortcut for validating an array of documents and inserting them into MongoDB if they're all valid. This function is faster than .create() because it only sends one operation to the server, rather than one for each document.

Mongoose always validates each document before sending insertMany to MongoDB. So if one document has a validation error, no documents will be saved, unless you set the ordered option to false.

This function does not trigger save middleware.

This function triggers the following middleware.

• insertMany()

Example:

const arr = [{ name: 'Star Wars' }, { name: 'The Empire Strikes Back' }];
Movies.insertMany(arr, function(error, docs) {});

Helper for console.log. Given a model named 'MyModel', returns the string 'Model { MyModel }'.

Example:

const MyModel = mongoose.model('Test', Schema({ name: String }));
MyModel.inspect(); // 'Model { Test }'
console.log(MyModel); // Prints 'Model { Test }'

Lists the indexes currently defined in MongoDB. This may or may not be the same as the indexes defined in your schema depending on whether you use the autoIndex option and if you build indexes manually.

Executes a mapReduce command.

o is an object specifying all mapReduce options as well as the map and reduce functions. All options are delegated to the driver implementation. See node-mongodb-native mapReduce() documentation for more detail about options.

This function does not trigger any middleware.

Example:

const o = {};
// `map()` and `reduce()` are run on the MongoDB server, not Node.js,
// these functions are converted to strings
o.map = function () { emit(this.name, 1) };
o.reduce = function (k, vals) { return vals.length };
User.mapReduce(o, function (err, results) {
  console.log(results)
})

Other options:

• query {Object} query filter object.
• sort {Object} sort input objects using this key
• limit {Number} max number of documents
• keeptemp {Boolean, default:false} keep temporary data
• finalize {Function} finalize function
• scope {Object} scope variables exposed to map/reduce/finalize during execution
• jsMode {Boolean, default:false} it is possible to make the execution stay in JS. Provided in MongoDB > 2.0.X
• verbose {Boolean, default:false} provide statistics on job execution time.
• readPreference {String}
• out* {Object, default: {inline:1}} sets the output target for the map reduce job.

* out options:

• {inline:1} the results are returned in an array
• {replace: 'collectionName'} add the results to collectionName: the results replace the collection
• {reduce: 'collectionName'} add the results to collectionName: if dups are detected, uses the reducer / finalize functions
• {merge: 'collectionName'} add the results to collectionName: if dups exist the new docs overwrite the old

If options.out is set to replace, merge, or reduce, a Model instance is returned that can be used for further querying. Queries run against this model are all executed with the lean option; meaning only the js object is returned and no Mongoose magic is applied (getters, setters, etc).

Example:

const o = {};
// You can also define `map()` and `reduce()` as strings if your
// linter complains about `emit()` not being defined
o.map = 'function () { emit(this.name, 1) }';
o.reduce = 'function (k, vals) { return vals.length }';
o.out = { replace: 'createdCollectionNameForResults' }
o.verbose = true;

User.mapReduce(o, function (err, model, stats) {
  console.log('map reduce took %d ms', stats.processtime)
  model.find().where('value').gt(10).exec(function (err, docs) {
    console.log(docs);
  });
})

// `mapReduce()` returns a promise. However, ES6 promises can only
// resolve to exactly one value,
o.resolveToObject = true;
const promise = User.mapReduce(o);
promise.then(function (res) {
  const model = res.model;
  const stats = res.stats;
  console.log('map reduce took %d ms', stats.processtime)
  return model.find().where('value').gt(10).exec();
}).then(function (docs) {
   console.log(docs);
}).then(null, handleError).end()

Populates document references.

Available top-level options:

• path: space delimited path(s) to populate
• select: optional fields to select
• match: optional query conditions to match
• model: optional name of the model to use for population
• options: optional query options like sort, limit, etc
• justOne: optional boolean, if true Mongoose will always set path to an array. Inferred from schema by default.

Examples:

// populates a single object
User.findById(id, function (err, user) {
  const opts = [
    { path: 'company', match: { x: 1 }, select: 'name' },
    { path: 'notes', options: { limit: 10 }, model: 'override' }
  ];

  User.populate(user, opts, function (err, user) {
    console.log(user);
  });
});

// populates an array of objects
User.find(match, function (err, users) {
  const opts = [{ path: 'company', match: { x: 1 }, select: 'name' }];

  const promise = User.populate(users, opts);
  promise.then(console.log).end();
})

// imagine a Weapon model exists with two saved documents:
//   { _id: 389, name: 'whip' }
//   { _id: 8921, name: 'boomerang' }
// and this schema:
// new Schema({
//   name: String,
//   weapon: { type: ObjectId, ref: 'Weapon' }
// });

const user = { name: 'Indiana Jones', weapon: 389 };
Weapon.populate(user, { path: 'weapon', model: 'Weapon' }, function (err, user) {
  console.log(user.weapon.name); // whip
})

// populate many plain objects
const users = [{ name: 'Indiana Jones', weapon: 389 }]
users.push({ name: 'Batman', weapon: 8921 })
Weapon.populate(users, { path: 'weapon' }, function (err, users) {
  users.forEach(function (user) {
    console.log('%s uses a %s', users.name, user.weapon.name)
    // Indiana Jones uses a whip
    // Batman uses a boomerang
  });
});
// Note that we didn't need to specify the Weapon model because
// it is in the schema's ref

Additional properties to attach to the query when calling save() and isNew is false.

Creates a Query and specifies a $where condition.

Sometimes you need to query for things in mongodb using a JavaScript expression. You can do so via find({ $where: javascript }), or you can use the mongoose shortcut method $where via a Query chain or from your mongoose Model.

Blog.$where('this.username.indexOf("val") !== -1').exec(function (err, docs) {});

Base Mongoose instance the model uses.

If this is a discriminator model, baseModelName is the name of the base model.

Collection the model uses.

This property is read-only. Modifying this property is a no-op.

Connection the model uses.

Alias for remove

Removes this document from the db. Equivalent to .remove().

Example:

product = await product.deleteOne();
await Product.findById(product._id); // null

Registered discriminators for this model.

Returns another Model instance.

Example:

const doc = new Tank;
doc.model('User').findById(id, callback);

The name of the model

Removes this document from the db.

Example:

product.remove(function (err, product) {
  if (err) return handleError(err);
  Product.findById(product._id, function (err, product) {
    console.log(product) // null
  })
})

As an extra measure of flow control, remove will return a Promise (bound to fn if passed) so it could be chained, or hooked to recieve errors

Example:

product.remove().then(function (product) {
   ...
}).catch(function (err) {
   assert.ok(err)
})

Saves this document by inserting a new document into the database if document.isNew is true, or sends an updateOne operation with just the modified paths if isNew is false.

Example:

product.sold = Date.now();
product = await product.save();

If save is successful, the returned promise will fulfill with the document saved.

Example:

const newProduct = await product.save();
newProduct === product; // true

Schema the model uses.

Removes all documents that match conditions from the collection. To remove just the first document that matches conditions, set the single option to true.

Example:

const res = await Character.remove({ name: 'Eddard Stark' });
res.deletedCount; // Number of documents removed

Note:

This method sends a remove command directly to MongoDB, no Mongoose documents are involved. Because no Mongoose documents are involved, Mongoose does not execute document middleware.

Same as update(), except MongoDB replace the existing document with the given document (no atomic operators like $set).

Example:

const res = await Person.replaceOne({ _id: 24601 }, { name: 'Jean Valjean' });
res.n; // Number of documents matched
res.nModified; // Number of documents modified

This function triggers the following middleware.

• replaceOne()

Requires MongoDB >= 3.6.0. Starts a MongoDB session for benefits like causal consistency, retryable writes, and transactions.

Calling MyModel.startSession() is equivalent to calling MyModel.db.startSession().

This function does not trigger any middleware.

Example:

const session = await Person.startSession();
let doc = await Person.findOne({ name: 'Ned Stark' }, null, { session });
await doc.remove();
// `doc` will always be null, even if reading from a replica set
// secondary. Without causal consistency, it is possible to
// get a doc back from the below query if the query reads from a
// secondary that is experiencing replication lag.
doc = await Person.findOne({ name: 'Ned Stark' }, null, { session, readPreference: 'secondary' });

Makes the indexes in MongoDB match the indexes defined in this model's schema. This function will drop any indexes that are not defined in the model's schema except the _id index, and build any indexes that are in your schema but not in MongoDB.

See the introductory blog post for more information.

Example:

const schema = new Schema({ name: { type: String, unique: true } });
const Customer = mongoose.model('Customer', schema);
await Customer.collection.createIndex({ age: 1 }); // Index is not in schema
// Will drop the 'age' index and create an index on `name`
await Customer.syncIndexes();

Translate any aliases fields/conditions so the final query or document object is pure

Example:

Character
  .find(Character.translateAliases({
    '名': 'Eddard Stark' // Alias for 'name'
  })
  .exec(function(err, characters) {})

Note:

Only translate arguments of object type anything else is returned raw

Updates one document in the database without returning it.

This function triggers the following middleware.

• update()

Examples:

MyModel.update({ age: { $gt: 18 } }, { oldEnough: true }, fn);

const res = await MyModel.update({ name: 'Tobi' }, { ferret: true });
res.n; // Number of documents that matched `{ name: 'Tobi' }`
// Number of documents that were changed. If every doc matched already
// had `ferret` set to `true`, `nModified` will be 0.
res.nModified;

Valid options:

• strict (boolean): overrides the schema-level strict option for this update
• upsert (boolean): whether to create the doc if it doesn't match (false)
• writeConcern (object): sets the write concern for replica sets. Overrides the schema-level write concern
• omitUndefined (boolean): If true, delete any properties whose value is undefined when casting an update. In other words, if this is set, Mongoose will delete baz from the update in Model.updateOne({}, { foo: 'bar', baz: undefined }) before sending the update to the server.
• multi (boolean): whether multiple documents should be updated (false)
• runValidators: if true, runs update validators on this command. Update validators validate the update operation against the model's schema.
• setDefaultsOnInsert (boolean): if this and upsert are true, mongoose will apply the defaults specified in the model's schema if a new document is created. This option only works on MongoDB >= 2.4 because it relies on MongoDB's $setOnInsert operator.
• timestamps (boolean): If set to false and schema-level timestamps are enabled, skip timestamps for this update. Does nothing if schema-level timestamps are not set.
• overwrite (boolean): disables update-only mode, allowing you to overwrite the doc (false)

All update values are cast to their appropriate SchemaTypes before being sent.

The callback function receives (err, rawResponse).

• err is the error if any occurred
• rawResponse is the full response from Mongo

Note:

All top level keys which are not atomic operation names are treated as set operations:

Example:

const query = { name: 'borne' };
Model.update(query, { name: 'jason bourne' }, options, callback);

// is sent as
Model.update(query, { $set: { name: 'jason bourne' }}, options, function(err, res));
// if overwrite option is false. If overwrite is true, sent without the $set wrapper.

This helps prevent accidentally overwriting all documents in your collection with { name: 'jason bourne' }.

Note:

Be careful to not use an existing model instance for the update clause (this won't work and can cause weird behavior like infinite loops). Also, ensure that the update clause does not have an _id property, which causes Mongo to return a "Mod on _id not allowed" error.

Note:

Mongoose casts values and runs setters when using update. The following features are not applied by default.

• defaults
• validators
• middleware

If you need document middleware and fully-featured validation, load the document first and then use save().

Model.findOne({ name: 'borne' }, function (err, doc) {
  if (err) ..
  doc.name = 'jason bourne';
  doc.save(callback);
})

Same as update(), except MongoDB will update all documents that match filter (as opposed to just the first one) regardless of the value of the multi option.

Note updateMany will not fire update middleware. Use pre('updateMany') and post('updateMany') instead.

Example:

const res = await Person.updateMany({ name: /Stark$/ }, { isDeleted: true });
res.n; // Number of documents matched
res.nModified; // Number of documents modified

This function triggers the following middleware.

• updateMany()

Same as update(), except it does not support the multi or overwrite options.

• MongoDB will update only the first document that matches filter regardless of the value of the multi option.
• Use replaceOne() if you want to overwrite an entire document rather than using atomic operators like $set.

Example:

const res = await Person.updateOne({ name: 'Jean-Luc Picard' }, { ship: 'USS Enterprise' });
res.n; // Number of documents matched
res.nModified; // Number of documents modified

This function triggers the following middleware.

• updateOne()

Casts and validates the given object against this model's schema, passing the given context to custom validators.

Example:

const Model = mongoose.model('Test', Schema({
  name: { type: String, required: true },
  age: { type: Number, required: true }
});

try {
  await Model.validate({ name: null }, ['name'])
} catch (err) {
  err instanceof mongoose.Error.ValidationError; // true
  Object.keys(err.errors); // ['name']
}

Requires a replica set running MongoDB >= 3.6.0. Watches the underlying collection for changes using MongoDB change streams.

This function does not trigger any middleware. In particular, it does not trigger aggregate middleware.

The ChangeStream object is an event emitter that emits the following events

• 'change': A change occurred, see below example
• 'error': An unrecoverable error occurred. In particular, change streams currently error out if they lose connection to the replica set primary. Follow this GitHub issue for updates.
• 'end': Emitted if the underlying stream is closed
• 'close': Emitted if the underlying stream is closed

Example:

const doc = await Person.create({ name: 'Ned Stark' });
const changeStream = Person.watch().on('change', change => console.log(change));
// Will print from the above `console.log()`:
// { _id: { _data: ... },
//   operationType: 'delete',
//   ns: { db: 'mydb', coll: 'Person' },
//   documentKey: { _id: 5a51b125c5500f5aa094c7bd } }
await doc.remove();

Creates a Query, applies the passed conditions, and returns the Query.

For example, instead of writing:

User.find({age: {$gte: 21, $lte: 65}}, callback);

we can instead write:

User.where('age').gte(21).lte(65).exec(callback);

Since the Query class also supports where you can continue chaining

User
.where('age').gte(21).lte(65)
.where('name', /^b/i)
... etc

Signal that we desire an increment of this documents version.

Example:

Model.findById(id, function (err, doc) {
  doc.increment();
  doc.save(function (err) { .. })
})