@skybloxsystems/ticket-bot/Bot/node_modules/mongoose/lib/model.js

Main

'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 PromiseProvider = require('./promise_provider');
const Query = require('./query');
const RemoveOptions = require('./options/removeOptions');
const SaveOptions = require('./options/saveOptions');
const Schema = require('./schema');
const ServerSelectionError = require('./error/serverSelection');
const ValidationError = require('./error/validation');
const VersionError = require('./error/version');
const ParallelSaveError = require('./error/parallelSave');
const applyQueryMiddleware = require('./helpers/query/applyQueryMiddleware');
const applyHooks = require('./helpers/model/applyHooks');
const applyMethods = require('./helpers/model/applyMethods');
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 createPopulateQueryFilter = require('./helpers/populate/createPopulateQueryFilter');
const getDefaultBulkwriteResult = require('./helpers/getDefaultBulkwriteResult');
const discriminator = require('./helpers/model/discriminator');
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 isPathSelectedInclusive = require('./helpers/projection/isPathSelectedInclusive');
const leanPopulateMap = require('./helpers/populate/leanPopulateMap');
const modifiedPaths = require('./helpers/update/modifiedPaths');
const parallelLimit = require('./helpers/parallelLimit');
const prepareDiscriminatorPipeline = require('./helpers/aggregate/prepareDiscriminatorPipeline');
const removeDeselectedForeignField = require('./helpers/populate/removeDeselectedForeignField');
const util = require('util');
const utils = require('./utils');

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
});

/**
 * A Model is a class that's your primary tool for interacting with MongoDB.
 * An instance of a Model is called a [Document](./api.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()`](./api.html#mongoose_Mongoose-model) and
 * [`connection.model()`](./api.html#connection_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' });
 *
 * @param {Object} doc values for initial set
 * @param [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](./api.html#query_Query-select).
 * @param {Boolean} [skipId=false] optional boolean. If true, mongoose doesn't add an `_id` field to the document.
 * @inherits Document http://mongoosejs.com/docs/api/document.html
 * @event `error`: If listening to this event, 'error' is emitted when a document was saved without passing a callback 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.
 */

Model.prototype.__proto__ = Document.prototype;
Model.prototype.$isMongooseModelPrototype = true;

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

Model.prototype.db;

/**
 * Collection the model uses.
 *
 * 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: 'notanid' }).catch(noop);
 *
 * @api public
 * @fires error whenever any query or model function errors
 * @memberOf Model
 * @static events
 */

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 _this = this;
  let 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')) {
    saveOptions.session = session;
  }

  if (Object.keys(saveOptions).length === 0) {
    saveOptions = null;
  }
  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, function(err, ret) {
      if (err) {
        _setIsNew(_this, true);

        callback(err, null);
        return;
      }

      callback(null, ret);
    });
    this.$__reset();
    _setIsNew(this, false);
    // Make it possible to retry the insert
    this.$__.inserting = true;
  } else {
    // 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, (err, ret) => {
        if (err) {
          this.$__undoReset();

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

          const matchedCount = 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) => {
    const hooks = this.$__schema.s.hooks;
    if (error) {
      return hooks.execPost('save:error', this, [this], { error: error }, (error) => {
        callback(error, this);
      });
    }
    let numAffected = 0;
    if (get(options, 'safe.w') !== 0 && get(options, 'w') !== 0) {
      // Skip checking if write succeeded if writeConcern is set to
      // unacknowledged writes, because otherwise `numAffected` will always be 0
      if (result != null) {
        if (Array.isArray(result)) {
          numAffected = result.length;
        } else if (result.matchedCount != null) {
          numAffected = result.matchedCount;
        } else {
          numAffected = result;
        }
      }
      // was this an update that required a version bump?
      if (this.$__.version && !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.$where,
          this.constructor.modelName, numAffected, result);
        return hooks.execPost('save:error', this, [this], { error: error }, (error) => {
          callback(error, this);
        });
      }
    }
    this.$__.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](/docs/api.html#document_Document-isNew) is `true`,
 * or sends an [updateOne](/docs/api.html#document_Document-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://docs.mongodb.com/manual/reference/server-sessions/) associated with this save operation. If not specified, defaults to the [document's associated session](api.html#document_Document-$session).
 * @param {Object} [options.safe] (DEPRECATED) overrides [schema's safe option](http://mongoosejs.com//docs/guide.html#safe). Use the `w` option instead.
 * @param {Boolean} [options.validateBeforeSave] set to false to save without validating.
 * @param {Boolean} [options.validateModifiedOnly=false] if `true`, Mongoose will only validate modified paths, as opposed to modified paths and `required` paths.
 * @param {Number|String} [options.w] set the [write concern](https://docs.mongodb.com/manual/reference/write-concern/#w-option). Overrides the [schema-level `writeConcern` option](/docs/guide.html#writeConcern)
 * @param {Boolean} [options.j] set to true for MongoDB to wait until this `save()` has been [journaled before resolving the returned promise](https://docs.mongodb.com/manual/reference/write-concern/#j-option). Overrides the [schema-level `writeConcern` option](/docs/guide.html#writeConcern)
 * @param {Number} [options.wtimeout] sets a [timeout for the write concern](https://docs.mongodb.com/manual/reference/write-concern/#wtimeout). Overrides the [schema-level `writeConcern` option](/docs/guide.html#writeConcern).
 * @param {Boolean} [options.checkKeys=true] the MongoDB driver prevents you from saving keys that start with '$' 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/#Restrictions-on-Field-Names)
 * @param {Boolean} [options.timestamps=true] if `false` and [timestamps](./guide.html#timestamps) are enabled, skip timestamps for this `save()`.
 * @param {Function} [fn] optional callback
 * @throws {DocumentNotFoundError} if this [save updates an existing document](api.html#document_Document-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|undefined} Returns undefined if used with callback or a Promise otherwise.
 * @api public
 * @see middleware http://mongoosejs.com/docs/middleware.html
 */

Model.prototype.save = function(options, fn) {
  let parallelSave;
  this.$op = 'save';

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

  if (typeof options === 'function') {
    fn = options;
    options = undefined;
  }

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

  fn = this.constructor.$handleCallbackError(fn);
  return this.constructor.db.base._promiseOrCallback(fn, cb => {
    cb = this.constructor.$wrapCallback(cb);

    if (parallelSave) {
      this.$__handleReject(parallelSave);
      return cb(parallelSave);
    }

    this.$__.saveOptions = options;

    this.$__save(options, error => {
      this.$__.saving = undefined;
      delete this.$__.saveOptions;
      delete this.$__.$versionError;
      this.$op = null;

      if (error) {
        this.$__handleReject(error);
        return cb(error);
      }
      cb(null, this);
    });
  }, this.constructor.events);
};

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
 */
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
 * @param {Object} delta
 * @param {Object} data
 * @param {Mixed} val
 * @param {String} [operation]
 */

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.$__schema.options.optimisticConcurrency) {
    self.$__.version = VERSION_ALL;
    return;
  }

  switch (op) {
    case '$set':
    case '$unset':
    case '$pop':
    case '$pull':
    case '$pullAll':
    case '$push':
    case '$addToSet':
      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') {
    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
 */

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();
  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 (get(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 (divergent.length) continue;
    if (value === undefined) {
      operand(this, where, delta, data, 1, '$unset');
    } else if (value === null) {
      operand(this, where, delta, data, null);
    } else if (value.isMongooseArray && value.$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 {
      value = utils.clone(value, {
        depopulate: true,
        transform: false,
        virtuals: false,
        getters: false,
        _isNested: true
      });
      operand(this, where, delta, data, value);
    }
  }

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

  if (this.$__.version) {
    this.$__version(where, delta);
  }
  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
 * @return {String|undefined}
 */

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 && array && array.isMongooseArray)) 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) {
      this.$__setValue(key, delta[key] = 0);
    }
    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;
    }
  }
};

/**
 * Signal that we desire an increment of this documents version.
 *
 * ####Example:
 *
 *     Model.findById(id, function (err, doc) {
 *       doc.increment();
 *       doc.save(function (err) { .. })
 *     })
 *
 * @see versionKeys http://mongoosejs.com/docs/guide.html#versionKey
 * @api public
 */

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

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.
 *
 * ####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 receive errors
 *
 * ####Example:
 *     product.remove().then(function (product) {
 *        ...
 *     }).catch(function (err) {
 *        assert.ok(err)
 *     })
 *
 * @param {Object} [options]
 * @param {Session} [options.session=null] the [session](https://docs.mongodb.com/manual/reference/server-sessions/) associated with this operation. If not specified, defaults to the [document's associated session](api.html#document_Document-$session).
 * @param {function(err,product)} [fn] optional callback
 * @return {Promise} Promise
 * @api public
 */

Model.prototype.remove = function remove(options, fn) {
  if (typeof options === 'function') {
    fn = options;
    options = undefined;
  }

  options = new RemoveOptions(options);
  if (options.hasOwnProperty('session')) {
    this.$session(options.session);
  }
  this.$op = 'remove';

  fn = this.constructor.$handleCallbackError(fn);

  return this.constructor.db.base._promiseOrCallback(fn, cb => {
    cb = this.constructor.$wrapCallback(cb);
    this.$__remove(options, (err, res) => {
      this.$op = null;
      cb(err, res);
    });
  }, this.constructor.events);
};

/*!
 * Alias for remove
 */

Model.prototype.$remove = Model.prototype.remove;
Model.prototype.delete = Model.prototype.remove;

/**
 * Removes this document from the db. Equivalent to `.remove()`.
 *
 * ####Example:
 *     product = await product.deleteOne();
 *     await Product.findById(product._id); // null
 *
 * @param {function(err,product)} [fn] optional callback
 * @return {Promise} Promise
 * @api public
 */

Model.prototype.deleteOne = function deleteOne(options, fn) {
  if (typeof options === 'function') {
    fn = options;
    options = undefined;
  }

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

  fn = this.constructor.$handleCallbackError(fn);

  return this.constructor.db.base._promiseOrCallback(fn, cb => {
    cb = this.constructor.$wrapCallback(cb);
    this.$__deleteOne(options, cb);
  }, this.constructor.events);
};

/*!
 * ignore
 */

Model.prototype.$__remove = function $__remove(options, cb) {
  if (this.$__.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, err => {
    if (!err) {
      this.$__.isDeleted = true;
      this.$emit('remove', this);
      this.constructor.emit('remove', this);
      return cb(null, this);
    }
    this.$__.isDeleted = false;
    cb(err);
  });
};

/*!
 * ignore
 */

Model.prototype.$__deleteOne = Model.prototype.$__remove;

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

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

/**
 * 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()`
 *
 * ####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()`](http://mongoosejs.com/docs/api.html#query_Query-setOptions)
 * @param {Function} [callback] callback
 * @return {Query}
 */

Model.exists = function exists(filter, options, callback) {
  _checkContext(this, 'exists');
  if (typeof options === 'function') {
    callback = options;
    options = null;
  }

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

  if (typeof callback === 'function') {
    return query.exec(callback);
  }
  options = options || {};
  if (!options.explain) {
    return query.then(doc => !!doc);
  }

  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.
 * @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 = get(options, 'clone', 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, true);
  if (this.db.models[name]) {
    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];
  d.prototype.__proto__ = 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
 */

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://docs.mongodb.com/manual/indexes/),
 * unless [`autoIndex`](http://mongoosejs.com/docs/guide.html#autoIndex) is turned off.
 *
 * Mongoose calls this function automatically when a model is created using
 * [`mongoose.model()`](/docs/api.html#mongoose_Mongoose-model) or
 * [`connection.model()`](/docs/api.html#connection_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')`](/docs/guide.html#indexes)
 *
 * ####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!');
 *     });
 *
 * @api public
 * @param {Function} [callback]
 * @returns {Promise}
 */

Model.init = function init(callback) {
  _checkContext(this, 'init');

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

  if (this.$init != null) {
    if (callback) {
      this.$init.then(() => callback(), err => callback(err));
      return null;
    }
    return this.$init;
  }

  const Promise = PromiseProvider.get();
  const autoIndex = utils.getOption('autoIndex',
    this.schema.options, this.db.config, this.db.base.options);
  const autoCreate = utils.getOption('autoCreate',
    this.schema.options, this.db.config, this.db.base.options);

  const _ensureIndexes = autoIndex ?
    cb => this.ensureIndexes({ _automatic: true }, cb) :
    cb => cb();
  const _createCollection = autoCreate ?
    cb => this.createCollection({}, cb) :
    cb => cb();

  this.$init = new Promise((resolve, reject) => {
    _createCollection(error => {
      if (error) {
        return reject(error);
      }
      _ensureIndexes(error => {
        if (error) {
          return reject(error);
        }
        resolve(this);
      });
    });
  });

  if (callback) {
    this.$init.then(() => callback(), err => callback(err));
    this.$caught = true;
    return null;
  } else {
    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://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!');
 *     });
 *
 * @api public
 * @param {Object} [options] see [MongoDB driver docs](http://mongodb.github.io/node-mongodb-native/3.1/api/Db.html#createCollection)
 * @param {Function} [callback]
 * @returns {Promise}
 */

Model.createCollection = function createCollection(options, callback) {
  _checkContext(this, 'createCollection');

  if (typeof options === 'string') {
    throw new MongooseError('You can\'t specify a new collection name in Model.createCollection.' +
      'This is not like Connection.createCollection. Only options are accepted here.');
  } else if (typeof options === 'function') {
    callback = options;
    options = void 0;
  }

  const schemaCollation = get(this, ['schema', 'options', 'collation'], null);
  if (schemaCollation != null) {
    options = Object.assign({ collation: schemaCollation }, options);
  }
  const capped = get(this, ['schema', 'options', 'capped']);
  if (capped) {
    options = Object.assign({ capped: true }, capped, options);
  }
  const timeseries = get(this, ['schema', 'options', 'timeseries']);
  if (timeseries != null) {
    options = Object.assign({ timeseries }, options);
  }

  callback = this.$handleCallbackError(callback);

  return this.db.base._promiseOrCallback(callback, cb => {
    cb = this.$wrapCallback(cb);

    this.db.createCollection(this.$__collection.collectionName, options, utils.tick((err) => {
      if (err != null && (err.name !== 'MongoServerError' || err.code !== 48)) {
        return cb(err);
      }
      this.$__collection = this.db.collection(this.$__collection.collectionName, options);
      cb(null, this.$__collection);
    }));
  }, this.events);
};

/**
 * 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](http://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();
 *
 * @param {Object} [options] options to pass to `ensureIndexes()`
 * @param {Boolean} [options.background=null] if specified, overrides each index's `background` property
 * @param {Function} [callback] optional callback
 * @return {Promise|undefined} Returns `undefined` if callback is specified, returns a promise if no callback.
 * @api public
 */

Model.syncIndexes = function syncIndexes(options, callback) {
  _checkContext(this, 'syncIndexes');

  callback = this.$handleCallbackError(callback);

  return this.db.base._promiseOrCallback(callback, cb => {
    cb = this.$wrapCallback(cb);

    this.createCollection(err => {
      if (err != null && (err.name !== 'MongoServerError' || err.code !== 48)) {
        return cb(err);
      }
      this.cleanIndexes((err, dropped) => {
        if (err != null) {
          return cb(err);
        }
        this.createIndexes(options, err => {
          if (err != null) {
            return cb(err);
          }
          cb(null, dropped);
        });
      });
    });
  }, this.events);
};

/**
 * Does a dry-run of Model.syncIndexes(), meaning that
 * the result of this function would be the result of
 * Model.syncIndexes().
 *
 * @param {Object} options not used at all.
 * @param {Function} callback optional callback
 * @returns {Promise} which containts an object, {toDrop, toCreate}, which
 * are indexes that would be dropped in mongodb and indexes that would be created in mongodb.
 */

Model.diffIndexes = function diffIndexes(options, callback) {
  const toDrop = [];
  const toCreate = [];
  callback = this.$handleCallbackError(callback);
  return this.db.base._promiseOrCallback(callback, cb => {
    cb = this.$wrapCallback(cb);
    this.listIndexes((err, indexes) => {
      if (indexes === undefined) {
        indexes = [];
      }
      const schemaIndexes = this.schema.indexes();
      // Iterate through the indexes created in mongodb and
      // compare against the indexes in the schema.
      for (const index of indexes) {
        let found = false;
        // Never try to drop `_id` index, MongoDB server doesn't allow it
        if (isDefaultIdIndex(index)) {
          continue;
        }

        for (const schemaIndex of schemaIndexes) {
          const key = schemaIndex[0];
          const options = _decorateDiscriminatorIndexOptions(this,
            utils.clone(schemaIndex[1]));
          if (isIndexEqual(key, options, index)) {
            found = true;
          }
        }

        if (!found) {
          toDrop.push(index.name);
        }
      }
      // Iterate through the indexes created on the schema and
      // compare against the indexes in mongodb.
      for (const schemaIndex of schemaIndexes) {
        const key = schemaIndex[0];
        let found = false;
        const options = _decorateDiscriminatorIndexOptions(this,
          utils.clone(schemaIndex[1]));
        for (const index of indexes) {
          if (isDefaultIdIndex(index)) {
            continue;
          }
          if (isIndexEqual(key, options, index)) {
            found = true;
          }
        }
        if (!found) {
          toCreate.push(key);
        }
      }
      cb(null, { toDrop, toCreate });
    });
  });
};

/**
 * 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
 *
 * @param {Function} [callback] optional callback
 * @return {Promise|undefined} Returns `undefined` if callback is specified, returns a promise if no callback.
 * @api public
 */

Model.cleanIndexes = function cleanIndexes(callback) {
  _checkContext(this, 'cleanIndexes');

  callback = this.$handleCallbackError(callback);

  return this.db.base._promiseOrCallback(callback, cb => {
    const collection = this.$__collection;

    this.listIndexes((err, indexes) => {
      if (err != null) {
        return cb(err);
      }

      const schemaIndexes = this.schema.indexes();
      const toDrop = [];

      for (const index of indexes) {
        let found = false;
        // Never try to drop `_id` index, MongoDB server doesn't allow it
        if (isDefaultIdIndex(index)) {
          continue;
        }

        for (const schemaIndex of schemaIndexes) {
          const key = schemaIndex[0];
          const options = _decorateDiscriminatorIndexOptions(this,
            utils.clone(schemaIndex[1]));
          if (isIndexEqual(key, options, index)) {
            found = true;
          }
        }

        if (!found) {
          toDrop.push(index.name);
        }
      }

      if (toDrop.length === 0) {
        return cb(null, []);
      }

      dropIndexes(toDrop, cb);
    });

    function dropIndexes(toDrop, cb) {
      let remaining = toDrop.length;
      let error = false;
      toDrop.forEach(indexName => {
        collection.dropIndex(indexName, err => {
          if (err != null) {
            error = true;
            return cb(err);
          }
          if (!error) {
            --remaining || cb(null, toDrop);
          }
        });
      });
    }
  });
};

/**
 * 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](/docs/guide.html#autoIndex) and if you
 * build indexes manually.
 *
 * @param {Function} [cb] optional callback
 * @return {Promise|undefined} Returns `undefined` if callback is specified, returns a promise if no callback.
 * @api public
 */

Model.listIndexes = function init(callback) {
  _checkContext(this, 'listIndexes');

  const _listIndexes = cb => {
    this.$__collection.listIndexes().toArray(cb);
  };

  callback = this.$handleCallbackError(callback);

  return this.db.base._promiseOrCallback(callback, cb => {
    cb = this.$wrapCallback(cb);

    // Buffering
    if (this.$__collection.buffer) {
      this.$__collection.addQueue(_listIndexes, [cb]);
    } else {
      _listIndexes(cb);
    }
  }, this.events);
};

/**
 * 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._
 *
 * @param {Object} [options] internal options
 * @param {Function} [cb] optional callback
 * @return {Promise}
 * @api public
 */

Mode