mongoose/lib/model.js

Mongoose MongoDB ODM

'use strict';

/*!
 * Module dependencies.
 */

const Aggregate = require('./aggregate');
const ChangeStream = require('./cursor/ChangeStream');
const Document = require('./document');
const DocumentNotFoundError = require('./error/notFound');
const DivergentArrayError = require('./error/divergentArray');
const EventEmitter = require('events').EventEmitter;
const MongooseBuffer = require('./types/buffer');
const MongooseError = require('./error/index');
const OverwriteModelError = require('./error/overwriteModel');
const Query = require('./query');
const SaveOptions = require('./options/saveOptions');
const Schema = require('./schema');
const ValidationError = require('./error/validation');
const VersionError = require('./error/version');
const ParallelSaveError = require('./error/parallelSave');
const applyDefaultsHelper = require('./helpers/document/applyDefaults');
const applyDefaultsToPOJO = require('./helpers/model/applyDefaultsToPOJO');
const applyQueryMiddleware = require('./helpers/query/applyQueryMiddleware');
const applyHooks = require('./helpers/model/applyHooks');
const applyMethods = require('./helpers/model/applyMethods');
const applyProjection = require('./helpers/projection/applyProjection');
const applySchemaCollation = require('./helpers/indexes/applySchemaCollation');
const applyStaticHooks = require('./helpers/model/applyStaticHooks');
const applyStatics = require('./helpers/model/applyStatics');
const applyWriteConcern = require('./helpers/schema/applyWriteConcern');
const assignVals = require('./helpers/populate/assignVals');
const castBulkWrite = require('./helpers/model/castBulkWrite');
const clone = require('./helpers/clone');
const createPopulateQueryFilter = require('./helpers/populate/createPopulateQueryFilter');
const getDefaultBulkwriteResult = require('./helpers/getDefaultBulkwriteResult');
const getSchemaDiscriminatorByValue = require('./helpers/discriminator/getSchemaDiscriminatorByValue');
const discriminator = require('./helpers/model/discriminator');
const firstKey = require('./helpers/firstKey');
const each = require('./helpers/each');
const get = require('./helpers/get');
const getConstructorName = require('./helpers/getConstructorName');
const getDiscriminatorByValue = require('./helpers/discriminator/getDiscriminatorByValue');
const getModelsMapForPopulate = require('./helpers/populate/getModelsMapForPopulate');
const immediate = require('./helpers/immediate');
const internalToObjectOptions = require('./options').internalToObjectOptions;
const isDefaultIdIndex = require('./helpers/indexes/isDefaultIdIndex');
const isIndexEqual = require('./helpers/indexes/isIndexEqual');
const {
  getRelatedDBIndexes,
  getRelatedSchemaIndexes
} = require('./helpers/indexes/getRelatedIndexes');
const isPathExcluded = require('./helpers/projection/isPathExcluded');
const decorateDiscriminatorIndexOptions = require('./helpers/indexes/decorateDiscriminatorIndexOptions');
const isPathSelectedInclusive = require('./helpers/projection/isPathSelectedInclusive');
const leanPopulateMap = require('./helpers/populate/leanPopulateMap');
const modifiedPaths = require('./helpers/update/modifiedPaths');
const parallelLimit = require('./helpers/parallelLimit');
const parentPaths = require('./helpers/path/parentPaths');
const prepareDiscriminatorPipeline = require('./helpers/aggregate/prepareDiscriminatorPipeline');
const pushNestedArrayPaths = require('./helpers/model/pushNestedArrayPaths');
const removeDeselectedForeignField = require('./helpers/populate/removeDeselectedForeignField');
const setDottedPath = require('./helpers/path/setDottedPath');
const STATES = require('./connectionstate');
const util = require('util');
const utils = require('./utils');
const MongooseBulkWriteError = require('./error/bulkWriteError');

const VERSION_WHERE = 1;
const VERSION_INC = 2;
const VERSION_ALL = VERSION_WHERE | VERSION_INC;

const arrayAtomicsSymbol = require('./helpers/symbols').arrayAtomicsSymbol;
const modelCollectionSymbol = Symbol('mongoose#Model#collection');
const modelDbSymbol = Symbol('mongoose#Model#db');
const modelSymbol = require('./helpers/symbols').modelSymbol;
const subclassedSymbol = Symbol('mongoose#Model#subclassed');

const saveToObjectOptions = Object.assign({}, internalToObjectOptions, {
  bson: true,
  flattenObjectIds: false
});

/**
 * A Model is a class that's your primary tool for interacting with MongoDB.
 * An instance of a Model is called a [Document](https://mongoosejs.com/docs/api/document.html#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()`](https://mongoosejs.com/docs/api/mongoose.html#Mongoose.prototype.model()) and
 * [`connection.model()`](https://mongoosejs.com/docs/api/connection.html#Connection.prototype.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' });
 *
 * @param {Object} doc values for initial set
 * @param {Object} [fields] optional object containing the fields that were selected in the query which returned this document. You do **not** need to set this parameter to ensure Mongoose handles your [query projection](https://mongoosejs.com/docs/api/query.html#Query.prototype.select()).
 * @param {Boolean} [skipId=false] optional boolean. If true, mongoose doesn't add an `_id` field to the document.
 * @inherits Document https://mongoosejs.com/docs/api/document.html
 * @event `error`: If listening to this event, 'error' is emitted when a document was saved and an `error` occurred. If not listening, the event bubbles to the connection used to create this Model.
 * @event `index`: Emitted after `Model#ensureIndexes` completes. If an error occurred it is passed with the event.
 * @event `index-single-start`: Emitted when an individual index starts within `Model#ensureIndexes`. The fields and options being used to build the index are also passed with the event.
 * @event `index-single-done`: Emitted when an individual index finishes within `Model#ensureIndexes`. If an error occurred it is passed with the event. The fields, options, and index name are also passed.
 * @api public
 */

function Model(doc, fields, skipId) {
  if (fields instanceof Schema) {
    throw new TypeError('2nd argument to `Model` must be a POJO or string, ' +
      '**not** a schema. Make sure you\'re calling `mongoose.model()`, not ' +
      '`mongoose.Model()`.');
  }
  Document.call(this, doc, fields, skipId);
}

/**
 * Inherits from Document.
 *
 * All Model.prototype features are available on
 * top level (non-sub) documents.
 * @api private
 */

Object.setPrototypeOf(Model.prototype, Document.prototype);
Model.prototype.$isMongooseModelPrototype = true;

/**
 * Connection the model uses.
 *
 * @api public
 * @property db
 * @memberOf Model
 * @instance
 */

Model.prototype.db;

/**
 * The collection instance this model uses.
 * A Mongoose collection is a thin wrapper around a [MongoDB Node.js driver collection]([MongoDB Node.js driver collection](https://mongodb.github.io/node-mongodb-native/Next/classes/Collection.html)).
 * Using `Model.collection` means you bypass Mongoose middleware, validation, and casting.
 *
 * This property is read-only. Modifying this property is a no-op.
 *
 * @api public
 * @property collection
 * @memberOf Model
 * @instance
 */

Model.prototype.collection;

/**
 * Internal collection the model uses.
 *
 * This property is read-only. Modifying this property is a no-op.
 *
 * @api private
 * @property collection
 * @memberOf Model
 * @instance
 */


Model.prototype.$__collection;

/**
 * The name of the model
 *
 * @api public
 * @property modelName
 * @memberOf Model
 * @instance
 */

Model.prototype.modelName;

/**
 * Additional properties to attach to the query when calling `save()` and
 * `isNew` is false.
 *
 * @api public
 * @property $where
 * @memberOf Model
 * @instance
 */

Model.prototype.$where;

/**
 * If this is a discriminator model, `baseModelName` is the name of
 * the base model.
 *
 * @api public
 * @property baseModelName
 * @memberOf Model
 * @instance
 */

Model.prototype.baseModelName;

/**
 * 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: 'Not a valid ObjectId' }).catch(noop);
 *
 * @api public
 * @property events
 * @fires error whenever any query or model function errors
 * @memberOf Model
 * @static
 */

Model.events;

/**
 * Compiled middleware for this model. Set in `applyHooks()`.
 *
 * @api private
 * @property _middleware
 * @memberOf Model
 * @static
 */

Model._middleware;

/*!
 * ignore
 */

function _applyCustomWhere(doc, where) {
  if (doc.$where == null) {
    return;
  }
  for (const key of Object.keys(doc.$where)) {
    where[key] = doc.$where[key];
  }
}

/*!
 * ignore
 */

Model.prototype.$__handleSave = function(options, callback) {
  const saveOptions = {};

  applyWriteConcern(this.$__schema, options);
  if (typeof options.writeConcern !== 'undefined') {
    saveOptions.writeConcern = {};
    if ('w' in options.writeConcern) {
      saveOptions.writeConcern.w = options.writeConcern.w;
    }
    if ('j' in options.writeConcern) {
      saveOptions.writeConcern.j = options.writeConcern.j;
    }
    if ('wtimeout' in options.writeConcern) {
      saveOptions.writeConcern.wtimeout = options.writeConcern.wtimeout;
    }
  } else {
    if ('w' in options) {
      saveOptions.w = options.w;
    }
    if ('j' in options) {
      saveOptions.j = options.j;
    }
    if ('wtimeout' in options) {
      saveOptions.wtimeout = options.wtimeout;
    }
  }
  if ('checkKeys' in options) {
    saveOptions.checkKeys = options.checkKeys;
  }

  const session = this.$session();
  if (!saveOptions.hasOwnProperty('session') && session != null) {
    saveOptions.session = session;
  }

  if (this.$isNew) {
    // send entire doc
    const obj = this.toObject(saveToObjectOptions);
    if ((obj || {})._id === void 0) {
      // documents must have an _id else mongoose won't know
      // what to update later if more changes are made. the user
      // wouldn't know what _id was generated by mongodb either
      // nor would the ObjectId generated by mongodb necessarily
      // match the schema definition.
      immediate(function() {
        callback(new MongooseError('document must have an _id before saving'));
      });
      return;
    }

    this.$__version(true, obj);
    this[modelCollectionSymbol].insertOne(obj, saveOptions).then(
      ret => callback(null, ret),
      err => {
        _setIsNew(this, true);

        callback(err, null);
      }
    );

    this.$__reset();
    _setIsNew(this, false);
    // Make it possible to retry the insert
    this.$__.inserting = true;
    return;
  }

  // Make sure we don't treat it as a new object on error,
  // since it already exists
  this.$__.inserting = false;
  const delta = this.$__delta();
  if (delta) {
    if (delta instanceof MongooseError) {
      callback(delta);
      return;
    }

    const where = this.$__where(delta[0]);
    if (where instanceof MongooseError) {
      callback(where);
      return;
    }

    _applyCustomWhere(this, where);
    this[modelCollectionSymbol].updateOne(where, delta[1], saveOptions).then(
      ret => {
        ret.$where = where;
        callback(null, ret);
      },
      err => {
        this.$__undoReset();

        callback(err);
      }
    );
  } else {
    const optionsWithCustomValues = Object.assign({}, options, saveOptions);
    const where = this.$__where();
    const optimisticConcurrency = this.$__schema.options.optimisticConcurrency;
    if (optimisticConcurrency && !Array.isArray(optimisticConcurrency)) {
      const key = this.$__schema.options.versionKey;
      const val = this.$__getValue(key);
      if (val != null) {
        where[key] = val;
      }
    }
    this.constructor.collection.findOne(where, optionsWithCustomValues)
      .then(documentExists => {
        const matchedCount = !documentExists ? 0 : 1;
        callback(null, { $where: where, matchedCount });
      })
      .catch(callback);
    return;
  }

  // store the modified paths before the document is reset
  this.$__.modifiedPaths = this.modifiedPaths();
  this.$__reset();

  _setIsNew(this, false);
};

/*!
 * ignore
 */

Model.prototype.$__save = function(options, callback) {
  this.$__handleSave(options, (error, result) => {
    if (error) {
      const hooks = this.$__schema.s.hooks;
      return hooks.execPost('save:error', this, [this], { error: error }, (error) => {
        callback(error, this);
      });
    }
    let numAffected = 0;
    const writeConcern = options != null ?
      options.writeConcern != null ?
        options.writeConcern.w :
        options.w :
      0;
    if (writeConcern !== 0) {
      // Skip checking if write succeeded if writeConcern is set to
      // unacknowledged writes, because otherwise `numAffected` will always be 0
      if (result != null) {
        if (Array.isArray(result)) {
          numAffected = result.length;
        } else if (result.matchedCount != null) {
          numAffected = result.matchedCount;
        } else {
          numAffected = result;
        }
      }

      const versionBump = this.$__.version;
      // was this an update that required a version bump?
      if (versionBump && !this.$__.inserting) {
        const doIncrement = VERSION_INC === (VERSION_INC & this.$__.version);
        this.$__.version = undefined;
        const key = this.$__schema.options.versionKey;
        const version = this.$__getValue(key) || 0;
        if (numAffected <= 0) {
          // the update failed. pass an error back
          this.$__undoReset();
          const err = this.$__.$versionError ||
            new VersionError(this, version, this.$__.modifiedPaths);
          return callback(err);
        }

        // increment version if was successful
        if (doIncrement) {
          this.$__setValue(key, version + 1);
        }
      }
      if (result != null && numAffected <= 0) {
        this.$__undoReset();
        error = new DocumentNotFoundError(result.$where,
          this.constructor.modelName, numAffected, result);
        const hooks = this.$__schema.s.hooks;
        return hooks.execPost('save:error', this, [this], { error: error }, (error) => {
          callback(error, this);
        });
      }
    }
    this.$__.saving = undefined;
    this.$__.savedState = {};
    this.$emit('save', this, numAffected);
    this.constructor.emit('save', this, numAffected);
    callback(null, this);
  });
};

/*!
 * ignore
 */

function generateVersionError(doc, modifiedPaths) {
  const key = doc.$__schema.options.versionKey;
  if (!key) {
    return null;
  }
  const version = doc.$__getValue(key) || 0;
  return new VersionError(doc, version, modifiedPaths);
}

/**
 * Saves this document by inserting a new document into the database if [document.isNew](https://mongoosejs.com/docs/api/document.html#Document.prototype.isNew) is `true`,
 * or sends an [updateOne](https://mongoosejs.com/docs/api/document.html#Document.prototype.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
 *
 * @param {Object} [options] options optional options
 * @param {Session} [options.session=null] the [session](https://www.mongodb.com/docs/manual/reference/server-sessions/) associated with this save operation. If not specified, defaults to the [document's associated session](https://mongoosejs.com/docs/api/document.html#Document.prototype.session()).
 * @param {Object} [options.safe] (DEPRECATED) overrides [schema's safe option](https://mongoosejs.com/docs/guide.html#safe). Use the `w` option instead.
 * @param {Boolean} [options.validateBeforeSave] set to false to save without validating.
 * @param {Boolean} [options.validateModifiedOnly=false] if `true`, Mongoose will only validate modified paths, as opposed to modified paths and `required` paths.
 * @param {Number|String} [options.w] set the [write concern](https://www.mongodb.com/docs/manual/reference/write-concern/#w-option). Overrides the [schema-level `writeConcern` option](https://mongoosejs.com/docs/guide.html#writeConcern)
 * @param {Boolean} [options.j] set to true for MongoDB to wait until this `save()` has been [journaled before resolving the returned promise](https://www.mongodb.com/docs/manual/reference/write-concern/#j-option). Overrides the [schema-level `writeConcern` option](https://mongoosejs.com/docs/guide.html#writeConcern)
 * @param {Number} [options.wtimeout] sets a [timeout for the write concern](https://www.mongodb.com/docs/manual/reference/write-concern/#wtimeout). Overrides the [schema-level `writeConcern` option](https://mongoosejs.com/docs/guide.html#writeConcern).
 * @param {Boolean} [options.checkKeys=true] the MongoDB driver prevents you from saving keys that start with '$' or contain '.' by default. Set this option to `false` to skip that check. See [restrictions on field names](https://docs.mongodb.com/manual/reference/limits/#mongodb-limit-Restrictions-on-Field-Names)
 * @param {Boolean} [options.timestamps=true] if `false` and [timestamps](https://mongoosejs.com/docs/guide.html#timestamps) are enabled, skip timestamps for this `save()`.
 * @throws {DocumentNotFoundError} if this [save updates an existing document](https://mongoosejs.com/docs/api/document.html#Document.prototype.isNew) but the document doesn't exist in the database. For example, you will get this error if the document is [deleted between when you retrieved the document and when you saved it](documents.html#updating).
 * @return {Promise}
 * @api public
 * @see middleware https://mongoosejs.com/docs/middleware.html
 */

Model.prototype.save = async function save(options) {
  if (typeof options === 'function' || typeof arguments[1] === 'function') {
    throw new MongooseError('Model.prototype.save() no longer accepts a callback');
  }

  let parallelSave;
  this.$op = 'save';

  if (this.$__.saving) {
    parallelSave = new ParallelSaveError(this);
  } else {
    this.$__.saving = new ParallelSaveError(this);
  }

  options = new SaveOptions(options);
  if (options.hasOwnProperty('session')) {
    this.$session(options.session);
  }
  if (this.$__.timestamps != null) {
    options.timestamps = this.$__.timestamps;
  }
  this.$__.$versionError = generateVersionError(this, this.modifiedPaths());

  if (parallelSave) {
    this.$__handleReject(parallelSave);
    throw parallelSave;
  }

  this.$__.saveOptions = options;

  await new Promise((resolve, reject) => {
    this.$__save(options, error => {
      this.$__.saving = null;
      this.$__.saveOptions = null;
      this.$__.$versionError = null;
      this.$op = null;
      if (error != null) {
        this.$__handleReject(error);
        return reject(error);
      }

      resolve();
    });
  });

  return this;
};

Model.prototype.$save = Model.prototype.save;

/**
 * Determines whether versioning should be skipped for the given path
 *
 * @param {Document} self
 * @param {String} path
 * @return {Boolean} true if versioning should be skipped for the given path
 * @api private
 */
function shouldSkipVersioning(self, path) {
  const skipVersioning = self.$__schema.options.skipVersioning;
  if (!skipVersioning) return false;

  // Remove any array indexes from the path
  path = path.replace(/\.\d+\./, '.');

  return skipVersioning[path];
}

/**
 * Apply the operation to the delta (update) clause as
 * well as track versioning for our where clause.
 *
 * @param {Document} self
 * @param {Object} where Unused
 * @param {Object} delta
 * @param {Object} data
 * @param {Mixed} val
 * @param {String} [op]
 * @api private
 */

function operand(self, where, delta, data, val, op) {
  // delta
  op || (op = '$set');
  if (!delta[op]) delta[op] = {};
  delta[op][data.path] = val;
  // disabled versioning?
  if (self.$__schema.options.versionKey === false) return;

  // path excluded from versioning?
  if (shouldSkipVersioning(self, data.path)) return;

  // already marked for versioning?
  if (VERSION_ALL === (VERSION_ALL & self.$__.version)) return;

  if (self.$__schema.options.optimisticConcurrency) {
    return;
  }

  switch (op) {
    case '$set':
    case '$unset':
    case '$pop':
    case '$pull':
    case '$pullAll':
    case '$push':
    case '$addToSet':
    case '$inc':
      break;
    default:
      // nothing to do
      return;
  }

  // ensure updates sent with positional notation are
  // editing the correct array element.
  // only increment the version if an array position changes.
  // modifying elements of an array is ok if position does not change.
  if (op === '$push' || op === '$addToSet' || op === '$pullAll' || op === '$pull') {
    if (/\.\d+\.|\.\d+$/.test(data.path)) {
      increment.call(self);
    } else {
      self.$__.version = VERSION_INC;
    }
  } else if (/^\$p/.test(op)) {
    // potentially changing array positions
    increment.call(self);
  } else if (Array.isArray(val)) {
    // $set an array
    increment.call(self);
  } else if (/\.\d+\.|\.\d+$/.test(data.path)) {
    // now handling $set, $unset
    // subpath of array
    self.$__.version = VERSION_WHERE;
  }
}

/**
 * Compiles an update and where clause for a `val` with _atomics.
 *
 * @param {Document} self
 * @param {Object} where
 * @param {Object} delta
 * @param {Object} data
 * @param {Array} value
 * @api private
 */

function handleAtomics(self, where, delta, data, value) {
  if (delta.$set && delta.$set[data.path]) {
    // $set has precedence over other atomics
    return;
  }

  if (typeof value.$__getAtomics === 'function') {
    value.$__getAtomics().forEach(function(atomic) {
      const op = atomic[0];
      const val = atomic[1];
      operand(self, where, delta, data, val, op);
    });
    return;
  }

  // legacy support for plugins

  const atomics = value[arrayAtomicsSymbol];
  const ops = Object.keys(atomics);
  let i = ops.length;
  let val;
  let op;

  if (i === 0) {
    // $set

    if (utils.isMongooseObject(value)) {
      value = value.toObject({ depopulate: 1, _isNested: true });
    } else if (value.valueOf) {
      value = value.valueOf();
    }

    return operand(self, where, delta, data, value);
  }

  function iter(mem) {
    return utils.isMongooseObject(mem)
      ? mem.toObject({ depopulate: 1, _isNested: true })
      : mem;
  }

  while (i--) {
    op = ops[i];
    val = atomics[op];

    if (utils.isMongooseObject(val)) {
      val = val.toObject({ depopulate: true, transform: false, _isNested: true });
    } else if (Array.isArray(val)) {
      val = val.map(iter);
    } else if (val.valueOf) {
      val = val.valueOf();
    }

    if (op === '$addToSet') {
      val = { $each: val };
    }

    operand(self, where, delta, data, val, op);
  }
}

/**
 * Produces a special query document of the modified properties used in updates.
 *
 * @api private
 * @method $__delta
 * @memberOf Model
 * @instance
 */

Model.prototype.$__delta = function() {
  const dirty = this.$__dirty();

  const optimisticConcurrency = this.$__schema.options.optimisticConcurrency;
  if (optimisticConcurrency) {
    if (Array.isArray(optimisticConcurrency)) {
      const optCon = new Set(optimisticConcurrency);
      const modPaths = this.modifiedPaths();
      if (modPaths.find(path => optCon.has(path))) {
        this.$__.version = dirty.length ? VERSION_ALL : VERSION_WHERE;
      }
    } else {
      this.$__.version = dirty.length ? VERSION_ALL : VERSION_WHERE;
    }
  }

  if (!dirty.length && VERSION_ALL !== this.$__.version) {
    return;
  }
  const where = {};
  const delta = {};
  const len = dirty.length;
  const divergent = [];
  let d = 0;

  where._id = this._doc._id;
  // If `_id` is an object, need to depopulate, but also need to be careful
  // because `_id` can technically be null (see gh-6406)
  if ((where && where._id && where._id.$__ || null) != null) {
    where._id = where._id.toObject({ transform: false, depopulate: true });
  }
  for (; d < len; ++d) {
    const data = dirty[d];
    let value = data.value;
    const match = checkDivergentArray(this, data.path, value);
    if (match) {
      divergent.push(match);
      continue;
    }

    const pop = this.$populated(data.path, true);
    if (!pop && this.$__.selected) {
      // If any array was selected using an $elemMatch projection, we alter the path and where clause
      // NOTE: MongoDB only supports projected $elemMatch on top level array.
      const pathSplit = data.path.split('.');
      const top = pathSplit[0];
      if (this.$__.selected[top] && this.$__.selected[top].$elemMatch) {
        // If the selected array entry was modified
        if (pathSplit.length > 1 && pathSplit[1] == 0 && typeof where[top] === 'undefined') {
          where[top] = this.$__.selected[top];
          pathSplit[1] = '$';
          data.path = pathSplit.join('.');
        }
        // if the selected array was modified in any other way throw an error
        else {
          divergent.push(data.path);
          continue;
        }
      }
    }

    // If this path is set to default, and either this path or one of
    // its parents is excluded, don't treat this path as dirty.
    if (this.$isDefault(data.path) && this.$__.selected) {
      if (data.path.indexOf('.') === -1 && isPathExcluded(this.$__.selected, data.path)) {
        continue;
      }

      const pathsToCheck = parentPaths(data.path);
      if (pathsToCheck.find(path => isPathExcluded(this.$__.isSelected, path))) {
        continue;
      }
    }

    if (divergent.length) continue;
    if (value === undefined) {
      operand(this, where, delta, data, 1, '$unset');
    } else if (value === null) {
      operand(this, where, delta, data, null);
    } else if (utils.isMongooseArray(value) && value.$path() && value[arrayAtomicsSymbol]) {
      // arrays and other custom types (support plugins etc)
      handleAtomics(this, where, delta, data, value);
    } else if (value[MongooseBuffer.pathSymbol] && Buffer.isBuffer(value)) {
      // MongooseBuffer
      value = value.toObject();
      operand(this, where, delta, data, value);
    } else {
      if (this.$__.primitiveAtomics && this.$__.primitiveAtomics[data.path] != null) {
        const val = this.$__.primitiveAtomics[data.path];
        const op = firstKey(val);
        operand(this, where, delta, data, val[op], op);
      } else {
        value = clone(value, {
          depopulate: true,
          transform: false,
          virtuals: false,
          getters: false,
          omitUndefined: true,
          _isNested: true
        });
        operand(this, where, delta, data, value);
      }
    }
  }

  if (divergent.length) {
    return new DivergentArrayError(divergent);
  }

  if (this.$__.version) {
    this.$__version(where, delta);
  }

  if (Object.keys(delta).length === 0) {
    return [where, null];
  }

  return [where, delta];
};

/**
 * Determine if array was populated with some form of filter and is now
 * being updated in a manner which could overwrite data unintentionally.
 *
 * @see https://github.com/Automattic/mongoose/issues/1334
 * @param {Document} doc
 * @param {String} path
 * @param {Any} array
 * @return {String|undefined}
 * @api private
 */

function checkDivergentArray(doc, path, array) {
  // see if we populated this path
  const pop = doc.$populated(path, true);

  if (!pop && doc.$__.selected) {
    // If any array was selected using an $elemMatch projection, we deny the update.
    // NOTE: MongoDB only supports projected $elemMatch on top level array.
    const top = path.split('.')[0];
    if (doc.$__.selected[top + '.$']) {
      return top;
    }
  }

  if (!(pop && utils.isMongooseArray(array))) return;

  // If the array was populated using options that prevented all
  // documents from being returned (match, skip, limit) or they
  // deselected the _id field, $pop and $set of the array are
  // not safe operations. If _id was deselected, we do not know
  // how to remove elements. $pop will pop off the _id from the end
  // of the array in the db which is not guaranteed to be the
  // same as the last element we have here. $set of the entire array
  // would be similarly destructive as we never received all
  // elements of the array and potentially would overwrite data.
  const check = pop.options.match ||
      pop.options.options && utils.object.hasOwnProperty(pop.options.options, 'limit') || // 0 is not permitted
      pop.options.options && pop.options.options.skip || // 0 is permitted
      pop.options.select && // deselected _id?
      (pop.options.select._id === 0 ||
      /\s?-_id\s?/.test(pop.options.select));

  if (check) {
    const atomics = array[arrayAtomicsSymbol];
    if (Object.keys(atomics).length === 0 || atomics.$set || atomics.$pop) {
      return path;
    }
  }
}

/**
 * Appends versioning to the where and update clauses.
 *
 * @api private
 * @method $__version
 * @memberOf Model
 * @instance
 */

Model.prototype.$__version = function(where, delta) {
  const key = this.$__schema.options.versionKey;
  if (where === true) {
    // this is an insert
    if (key) {
      setDottedPath(delta, key, 0);
      this.$__setValue(key, 0);
    }
    return;
  }

  if (key === false) {
    return;
  }

  // updates

  // only apply versioning if our versionKey was selected. else
  // there is no way to select the correct version. we could fail
  // fast here and force them to include the versionKey but
  // thats a bit intrusive. can we do this automatically?

  if (!this.$__isSelected(key)) {
    return;
  }

  // $push $addToSet don't need the where clause set
  if (VERSION_WHERE === (VERSION_WHERE & this.$__.version)) {
    const value = this.$__getValue(key);
    if (value != null) where[key] = value;
  }

  if (VERSION_INC === (VERSION_INC & this.$__.version)) {
    if (get(delta.$set, key, null) != null) {
      // Version key is getting set, means we'll increment the doc's version
      // after a successful save, so we should set the incremented version so
      // future saves don't fail (gh-5779)
      ++delta.$set[key];
    } else {
      delta.$inc = delta.$inc || {};
      delta.$inc[key] = 1;
    }
  }
};

/*!
 * ignore
 */

function increment() {
  this.$__.version = VERSION_ALL;
  return this;
}

/**
 * Signal that we desire an increment of this documents version.
 *
 * #### Example:
 *
 *     const doc = await Model.findById(id);
 *     doc.increment();
 *     await doc.save();
 *
 * @see versionKeys https://mongoosejs.com/docs/guide.html#versionKey
 * @memberOf Model
 * @method increment
 * @api public
 */

Model.prototype.increment = increment;

/**
 * Returns a query object
 *
 * @api private
 * @method $__where
 * @memberOf Model
 * @instance
 */

Model.prototype.$__where = function _where(where) {
  where || (where = {});

  if (!where._id) {
    where._id = this._doc._id;
  }

  if (this._doc._id === void 0) {
    return new MongooseError('No _id found on document!');
  }

  return where;
};

/**
 * Removes this document from the db. Equivalent to `.remove()`.
 *
 * #### Example:
 *
 *     product = await product.deleteOne();
 *     await Product.findById(product._id); // null
 *
 * @return {Promise} Promise
 * @api public
 */

Model.prototype.deleteOne = async function deleteOne(options) {
  if (typeof options === 'function' ||
      typeof arguments[1] === 'function') {
    throw new MongooseError('Model.prototype.deleteOne() no longer accepts a callback');
  }

  if (!options) {
    options = {};
  }

  if (options.hasOwnProperty('session')) {
    this.$session(options.session);
  }

  const res = await new Promise((resolve, reject) => {
    this.$__deleteOne(options, (err, res) => {
      if (err != null) {
        return reject(err);
      }
      resolve(res);
    });
  });

  return res;
};

/*!
 * ignore
 */

Model.prototype.$__deleteOne = function $__deleteOne(options, cb) {
  if (this.$__.isDeleted) {
    return immediate(() => cb(null, this));
  }

  const where = this.$__where();
  if (where instanceof MongooseError) {
    return cb(where);
  }

  _applyCustomWhere(this, where);

  const session = this.$session();
  if (!options.hasOwnProperty('session')) {
    options.session = session;
  }

  this[modelCollectionSymbol].deleteOne(where, options).then(
    () => {
      this.$__.isDeleted = true;
      this.$emit('deleteOne', this);
      this.constructor.emit('deleteOne', this);
      return cb(null, this);
    },
    err => {
      this.$__.isDeleted = false;
      cb(err);
    }
  );
};

/**
 * Returns another Model instance.
 *
 * #### Example:
 *
 *     const doc = new Tank;
 *     await doc.model('User').findById(id);
 *
 * @param {String} name model name
 * @method model
 * @api public
 * @return {Model}
 */

Model.prototype.model = function model(name) {
  return this[modelDbSymbol].model(name);
};

/**
 * Returns another Model instance.
 *
 * #### Example:
 *
 *     const doc = new Tank;
 *     await doc.model('User').findById(id);
 *
 * @param {String} name model name
 * @method $model
 * @api public
 * @return {Model}
 */

Model.prototype.$model = function $model(name) {
  return this[modelDbSymbol].model(name);
};

/**
 * Returns a document with `_id` only if at least one document exists in the database that matches
 * the given `filter`, and `null` otherwise.
 *
 * Under the hood, `MyModel.exists({ answer: 42 })` is equivalent to
 * `MyModel.findOne({ answer: 42 }).select({ _id: 1 }).lean()`
 *
 * #### Example:
 *
 *     await Character.deleteMany({});
 *     await Character.create({ name: 'Jean-Luc Picard' });
 *
 *     await Character.exists({ name: /picard/i }); // { _id: ... }
 *     await Character.exists({ name: /riker/i }); // null
 *
 * This function triggers the following middleware.
 *
 * - `findOne()`
 *
 * @param {Object} filter
 * @param {Object} [options] optional see [`Query.prototype.setOptions()`](https://mongoosejs.com/docs/api/query.html#Query.prototype.setOptions())
 * @return {Query}
 */

Model.exists = function exists(filter, options) {
  _checkContext(this, 'exists');
  if (typeof arguments[2] === 'function') {
    throw new MongooseError('Model.exists() no longer accepts a callback');
  }

  const query = this.findOne(filter).
    select({ _id: 1 }).
    lean().
    setOptions(options);

  return query;
};

/**
 * 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
 *
 * @param {String} name discriminator model name
 * @param {Schema} schema discriminator model schema
 * @param {Object|String} [options] If string, same as `options.value`.
 * @param {String} [options.value] the string stored in the `discriminatorKey` property. If not specified, Mongoose uses the `name` parameter.
 * @param {Boolean} [options.clone=true] By default, `discriminator()` clones the given `schema`. Set to `false` to skip cloning.
 * @param {Boolean} [options.overwriteModels=false] by default, Mongoose does not allow you to define a discriminator with the same name as another discriminator. Set this to allow overwriting discriminators with the same name.
 * @param {Boolean} [options.mergeHooks=true] By default, Mongoose merges the base schema's hooks with the discriminator schema's hooks. Set this option to `false` to make Mongoose use the discriminator schema's hooks instead.
 * @param {Boolean} [options.mergePlugins=true] By default, Mongoose merges the base schema's plugins with the discriminator schema's plugins. Set this option to `false` to make Mongoose use the discriminator schema's plugins instead.
 * @return {Model} The newly created discriminator model
 * @api public
 */

Model.discriminator = function(name, schema, options) {
  let model;
  if (typeof name === 'function') {
    model = name;
    name = utils.getFunctionName(model);
    if (!(model.prototype instanceof Model)) {
      throw new MongooseError('The provided class ' + name + ' must extend Model');
    }
  }

  options = options || {};
  const value = utils.isPOJO(options) ? options.value : options;
  const clone = typeof options.clone === 'boolean' ? options.clone : true;
  const mergePlugins = typeof options.mergePlugins === 'boolean' ? options.mergePlugins : true;

  _checkContext(this, 'discriminator');

  if (utils.isObject(schema) && !schema.instanceOfSchema) {
    schema = new Schema(schema);
  }
  if (schema instanceof Schema && clone) {
    schema = schema.clone();
  }

  schema = discriminator(this, name, schema, value, mergePlugins, options.mergeHooks);
  if (this.db.models[name] && !schema.options.overwriteModels) {
    throw new OverwriteModelError(name);
  }

  schema.$isRootDiscriminator = true;
  schema.$globalPluginsApplied = true;

  model = this.db.model(model || name, schema, this.$__collection.name);
  this.discriminators[name] = model;
  const d = this.discriminators[name];
  Object.setPrototypeOf(d.prototype, this.prototype);
  Object.defineProperty(d, 'baseModelName', {
    value: this.modelName,
    configurable: true,
    writable: false
  });

  // apply methods and statics
  applyMethods(d, schema);
  applyStatics(d, schema);

  if (this[subclassedSymbol] != null) {
    for (const submodel of this[subclassedSymbol]) {
      submodel.discriminators = submodel.discriminators || {};
      submodel.discriminators[name] =
        model.__subclass(model.db, schema, submodel.collection.name);
    }
  }

  return d;
};

/**
 * Make sure `this` is a model
 * @api private
 */

function _checkContext(ctx, fnName) {
  // Check context, because it is easy to mistakenly type
  // `new Model.discriminator()` and get an incomprehensible error
  if (ctx == null || ctx === global) {
    throw new MongooseError('`Model.' + fnName + '()` cannot run without a ' +
      'model as `this`. Make sure you are calling `MyModel.' + fnName + '()` ' +
      'where `MyModel` is a Mongoose model.');
  } else if (ctx[modelSymbol] == null) {
    throw new MongooseError('`Model.' + fnName + '()` cannot run without a ' +
      'model as `this`. Make sure you are not calling ' +
      '`new Model.' + fnName + '()`');
  }
}

// Model (class) features

/*!
 * Give the constructor the ability to emit events.
 */

for (const i in EventEmitter.prototype) {
  Model[i] = EventEmitter.prototype[i];
}

/**
 * This function is responsible for building [indexes](https://www.mongodb.com/docs/manual/indexes/),
 * unless [`autoIndex`](https://mongoosejs.com/docs/guide.html#autoIndex) is turned off.
 *
 * Mongoose calls this function automatically when a model is created using
 * [`mongoose.model()`](https://mongoosejs.com/docs/api/mongoose.html#Mongoose.prototype.model()) or
 * [`connection.model()`](https://mongoosejs.com/docs/api/connection.html#Connection.prototype.model()), so you
 * don't need to call `init()` to trigger index builds.
 *
 * However, you _may_ need to call `init()`  to get back a promise that will resolve when your indexes are finished.
 * Calling `await Model.init()` is helpful if you need to wait for indexes to build before continuing.
 * For example, if you want to wait for unique indexes to build before continuing with a test case.
 *
 * #### 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);
 *
 *     await Event.init();
 *     console.log('Indexes are done building!');
 *
 * @api public
 * @returns {Promise}
 */

Model.init = function init() {
  _checkContext(this, 'init');
  if (typeof arguments[0] === 'function') {
    throw new MongooseError('Model.init() no longer accepts a callback');
  }

  this.schema.emit('init', this);

  if (this.$init != null) {
    return this.$init;
  }

  const conn = this.db;
  const _ensureIndexes = async() => {
    const autoIndex = utils.getOption(
      'autoIndex',
      this.schema.options,
      conn.config,
      conn.base.options
    );
    if (!autoIndex) {
      return;
    }
    return await this.ensureIndexes({ _automatic: true });
  };
  const _createCollection = async() => {
    if ((conn.readyState === STATES.connecting || conn.readyState === STATES.disconnected) && conn._shouldBufferCommands()) {
      await new Promise(resolve => {
        conn._queue.push({ fn: resolve });
      });
    }
    const autoCreate = utils.getOption(
      'autoCreate',
      this.schema.options,
      conn.config,
      conn.base.options
    );
    if (!autoCreate) {
      return;
    }
    return await this.createCollection();
  };

  this.$init = _createCollection().then(() => _ensureIndexes());

  const _catch = this.$init.catch;
  const _this = this;
  this.$init.catch = function() {
    _this.$caught = true;
    return _catch.apply(_this.$init, arguments);
  };

  return this.$init;
};


/**
 * 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://www.mongodb.com/docs/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!');
 *     });
 *
 * @api public
 * @param {Object} [options] see [MongoDB driver docs](https://mongodb.github.io/node-mongodb-native/4.9/classes/Db.html#createCollection)
 * @returns {Promise}
 */

Model.createCollection = async function createCollection(options) {
  _checkContext(this, 'createCollection');
  if (typeof arguments[0] === 'function' || typeof arguments[1] === 'function') {
    throw new MongooseError('Model.createCollection() no longer accepts a callback');
  }

  const collectionOptions = this &&
    this.schema &&
    this.schema.options &&
    this.schema.options.collectionOptions;
  if (collectionOptions != null) {
    options = Object.assign({}, collectionOptions, options);
  }

  const schemaCollation = this &&
    this.schema &&
    this.schema.options &&
    this.schema.options.collation;
  if (schemaCollation != null) {
    options = Object.assign({ collation: schemaCollation }, options);
  }
  const capped = this &&
    this.schema &&
    this.schema.options &&
    this.schema.options.capped;
  if (capped != null) {
    if (typeof capped === 'number') {
      options = Object.assign({ capped: true, size: capped }, options);
    } else if (typeof capped === 'object') {
      options = Object.assign({ capped: true }, capped, options);
    }
  }
  const timeseries = this &&
    this.schema &&
    this.schema.options &&
    this.schema.options.timeseries;
  if (timeseries != null) {
    options = Object.assign({ timeseries }, options);
    if (options.expireAfterSeconds != null) {
      // do nothing
    } else if (options.expires != null) {
      utils.expires(options);
    } else if (this.schema.options.expireAfterSeconds != null) {
      options.expireAfterSeconds = this.schema.options.expireAfterSeconds;
    } else if (this.schema.options.expires != null) {
      options.expires = this.schema.options.expires;
      utils.expires(options);
    }
  }

  const clusteredIndex = this &&
    this.schema &&
    this.schema.options &&
    this.schema.options.clusteredIndex;
  if (clusteredIndex != null) {
    options = Object.assign({ clusteredIndex: { ...clusteredIndex, unique: true } }, options);
  }

  try {
    await this.db.createCollection(this.$__collection.collectionName, options);
  } catch (err) {

    if (err != null && (err.name !== 'MongoServerError' || err.code !== 48)) {
      throw err;
    }
  }
  return this.$__collection;
};

/**
 * 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](https://thecodebarbarian.com/whats-new-in-mongoose-5-2-syncindexes)
 * 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();
 *
 * You should be careful about running `syncIndexes()` on production applications under heavy load,
 * because index builds are expensive operations, and unexpected index drops can lead to degraded
 * performance. Before running `syncIndexes()`, you can use the [`diffIndexes()` function](#Model.diffIndexes())
 * to check what indexes `syncIndexes()` will drop and create.
 *
 * #### Example:
 *
 *     const { toDrop, toCreate } = await Model.diffIndexes();
 *     toDrop; // Array of strings containing names of indexes that `syncIndexes()` will drop
 *     toCreate; // Array of strings containing names of indexes that `syncIndexes()` will create
 *
 * @param {Object} [options] options to pass to `ensureIndexes()`
 * @param {Boolean} [options.background=null] if specified, overrides each index's `background` property
 * @return {Promise}
 * @api public
 */

Model.syncIndexes = async function syncIndexes(options) {
  _checkContext(this, 'syncIndexes');
  if (typeof arguments[0] === 'function' || typeof arguments[1] === 'function') {
    throw new MongooseError('Model.syncIndexes() no longer accepts a callback');
  }

  const model = this;

  try {
    await model.createCollection();
  } catch (err) {
    if (err != null && (err.name !== 'MongoServerError' || err.code !== 48)) {
      throw err;
    }
  }

  const diffIndexesResult = await model.diffIndexes();
  const dropped = await model.cleanIndexes({ ...options, toDrop: diffIndexesResult.toDrop });
  await model.createIndexes({ ...options, toCreate: diffIndexesResult.toCreate });

  return dropped;
};

/**
 * Does a dry-run of `Model.syncIndexes()`, returning the indexes that `syncIndexes()` would drop and create if you were to run `syncIndexes()`.
 *
 * #### Example:
 *
 *     const { toDrop, toCreate } = await Model.diffIndexes();
 *     toDrop; // Array of strings containing names of indexes that `syncIndexes()` will drop
 *     toCreate; // Array of strings containing names of indexes that `syncIndexes()` will create
 *
 * @param {Object} [options]
 * @return {Promise<Object>} contains the indexes that would be dropped in MongoDB and indexes that would be created in MongoDB as `{ toDrop: string[], toCreate: string[] }`.
 */

Model.diffIndexes = async function diffIndexes() {
  if (typeof arguments[0] === 'function' || typeof arguments[1] === 'function') {
    throw new MongooseError('Model.syncIndexes() no longer accepts a callback');
  }

  const model = this;

  let dbIndexes = await model.listIndexes();
  if (dbIndexes === undefined) {
    dbIndexes = [];
  }
  dbIndexes = getRelatedDBIndexes(model, dbIndexes);

  const schema = model.schema;
  const schemaIndexes = getRelatedSchemaIndexes(model, schema.indexes());

  const toDrop = getIndexesToDrop(schema, schemaIndexes, dbIndexes);
  const toCreate = getIndexesToCreate(schema, schemaIndexes, dbIndexes, toDrop);

  return { toDrop, toCreate };
};

function getIndexesToCreate(schema, schemaIndexes, dbIndexes, toDrop) {
  const toCreate = [];

  for (const [schemaIndexKeysObject, schemaIndexOptions] of schemaIndexes) {
    let found = false;

    const options = decorateDiscriminatorIndexOptions(schema, clone(schemaIndexOptions));

    for (const index of dbIndexes) {
      if (isDefaultIdIndex(index)) {
        continue;
      }
      if (
        isIndexEqual(schemaIndexKeysObject, options, index) &&
        !toDrop.includes(index.name)
      ) {
        found = true;
        break;
      }
    }

    if (!found) {
      toCreate.push(schemaIndexKey