Commit

node_modules/mongoose/lib/helpers/populate/getModelsMapForPopulate.js

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+'use strict';
+
+const MongooseError = require('../../error/index');
+const SkipPopulateValue = require('./skipPopulateValue');
+const clone = require('../clone');
+const get = require('../get');
+const getDiscriminatorByValue = require('../discriminator/getDiscriminatorByValue');
+const getConstructorName = require('../getConstructorName');
+const getSchemaTypes = require('./getSchemaTypes');
+const getVirtual = require('./getVirtual');
+const lookupLocalFields = require('./lookupLocalFields');
+const mpath = require('mpath');
+const modelNamesFromRefPath = require('./modelNamesFromRefPath');
+const utils = require('../../utils');
+
+const modelSymbol = require('../symbols').modelSymbol;
+const populateModelSymbol = require('../symbols').populateModelSymbol;
+const schemaMixedSymbol = require('../../schema/symbols').schemaMixedSymbol;
+const StrictPopulate = require('../../error/strictPopulate');
+
+module.exports = function getModelsMapForPopulate(model, docs, options) {
+  let doc;
+  const len = docs.length;
+  const map = [];
+  const modelNameFromQuery = options.model && options.model.modelName || options.model;
+  let schema;
+  let refPath;
+  let modelNames;
+  const available = {};
+
+  const modelSchema = model.schema;
+
+  // Populating a nested path should always be a no-op re: #9073.
+  // People shouldn't do this, but apparently they do.
+  if (options._localModel != null && options._localModel.schema.nested[options.path]) {
+    return [];
+  }
+
+  const _virtualRes = getVirtual(model.schema, options.path);
+  const virtual = _virtualRes == null ? null : _virtualRes.virtual;
+  if (virtual != null) {
+    return _virtualPopulate(model, docs, options, _virtualRes);
+  }
+
+  let allSchemaTypes = getSchemaTypes(model, modelSchema, null, options.path);
+  allSchemaTypes = Array.isArray(allSchemaTypes) ? allSchemaTypes : [allSchemaTypes].filter(v => v != null);
+
+  const isStrictPopulateDisabled = options.strictPopulate === false || options.options?.strictPopulate === false;
+  if (!isStrictPopulateDisabled && allSchemaTypes.length === 0 && options._localModel != null) {
+    return new StrictPopulate(options._fullPath || options.path);
+  }
+
+  for (let i = 0; i < len; i++) {
+    doc = docs[i];
+    let justOne = null;
+
+    if (doc.$__ != null && doc.populated(options.path)) {
+      const forceRepopulate = options.forceRepopulate != null ? options.forceRepopulate : doc.constructor.base.options.forceRepopulate;
+      if (forceRepopulate === false) {
+        continue;
+      }
+    }
+
+    const docSchema = doc != null && doc.$__ != null ? doc.$__schema : modelSchema;
+    schema = getSchemaTypes(model, docSchema, doc, options.path);
+
+    // Special case: populating a path that's a DocumentArray unless
+    // there's an explicit `ref` or `refPath` re: gh-8946
+    if (schema != null &&
+        schema.$isMongooseDocumentArray &&
+        schema.options.ref == null &&
+        schema.options.refPath == null) {
+      continue;
+    }
+    const isUnderneathDocArray = schema && schema.$parentSchemaDocArray;
+    if (isUnderneathDocArray && get(options, 'options.sort') != null) {
+      return new MongooseError('Cannot populate with `sort` on path ' + options.path +
+        ' because it is a subproperty of a document array');
+    }
+
+    modelNames = null;
+    let isRefPath = false;
+    let normalizedRefPath = null;
+    let schemaOptions = null;
+    let modelNamesInOrder = null;
+
+    if (schema != null && schema.instance === 'Embedded') {
+      if (schema.options.ref) {
+        const data = {
+          localField: options.path + '._id',
+          foreignField: '_id',
+          justOne: true
+        };
+        const res = _getModelNames(doc, schema, modelNameFromQuery, model);
+
+        const unpopulatedValue = mpath.get(options.path, doc);
+        const id = mpath.get('_id', unpopulatedValue);
+        addModelNamesToMap(model, map, available, res.modelNames, options, data, id, doc, schemaOptions, unpopulatedValue);
+      }
+      // No-op if no `ref` set. See gh-11538
+      continue;
+    }
+
+    if (Array.isArray(schema)) {
+      const schemasArray = schema;
+      for (const _schema of schemasArray) {
+        let _modelNames;
+        let res;
+        try {
+          res = _getModelNames(doc, _schema, modelNameFromQuery, model);
+          _modelNames = res.modelNames;
+          isRefPath = isRefPath || res.isRefPath;
+          normalizedRefPath = normalizedRefPath || res.refPath;
+          justOne = res.justOne;
+        } catch (error) {
+          return error;
+        }
+
+        if (isRefPath && !res.isRefPath) {
+          continue;
+        }
+        if (!_modelNames) {
+          continue;
+        }
+        modelNames = modelNames || [];
+        for (const modelName of _modelNames) {
+          if (modelNames.indexOf(modelName) === -1) {
+            modelNames.push(modelName);
+          }
+        }
+      }
+    } else {
+      try {
+        const res = _getModelNames(doc, schema, modelNameFromQuery, model);
+        modelNames = res.modelNames;
+        isRefPath = res.isRefPath;
+        normalizedRefPath = normalizedRefPath || res.refPath;
+        justOne = res.justOne;
+        schemaOptions = get(schema, 'options.populate', null);
+        // Dedupe, because `refPath` can return duplicates of the same model name,
+        // and that causes perf issues.
+        if (isRefPath) {
+          modelNamesInOrder = modelNames;
+          modelNames = Array.from(new Set(modelNames));
+        }
+      } catch (error) {
+        return error;
+      }
+
+      if (!modelNames) {
+        continue;
+      }
+    }
+
+    const data = {};
+    const localField = options.path;
+    const foreignField = '_id';
+
+    // `justOne = null` means we don't know from the schema whether the end
+    // result should be an array or a single doc. This can result from
+    // populating a POJO using `Model.populate()`
+    if ('justOne' in options && options.justOne !== void 0) {
+      justOne = options.justOne;
+    } else if (schema && !schema[schemaMixedSymbol]) {
+      // Skip Mixed types because we explicitly don't do casting on those.
+      if (options.path.endsWith('.' + schema.path) || options.path === schema.path) {
+        justOne = Array.isArray(schema) ?
+          schema.every(schema => !schema.$isMongooseArray) :
+          !schema.$isMongooseArray;
+      }
+    }
+
+    if (!modelNames) {
+      continue;
+    }
+
+    data.isVirtual = false;
+    data.justOne = justOne;
+    data.localField = localField;
+    data.foreignField = foreignField;
+
+    // Get local fields
+    const ret = _getLocalFieldValues(doc, localField, model, options, null, schema);
+
+    const id = String(utils.getValue(foreignField, doc));
+    options._docs[id] = Array.isArray(ret) ? ret.slice() : ret;
+
+    let match = get(options, 'match', null);
+
+    const hasMatchFunction = typeof match === 'function';
+    if (hasMatchFunction) {
+      match = match.call(doc, doc);
+    }
+    throwOn$where(match);
+    data.match = match;
+    data.hasMatchFunction = hasMatchFunction;
+    data.isRefPath = isRefPath;
+    data.modelNamesInOrder = modelNamesInOrder;
+
+    if (isRefPath) {
+      const embeddedDiscriminatorModelNames = _findRefPathForDiscriminators(doc,
+        modelSchema, data, options, normalizedRefPath, ret);
+
+      modelNames = embeddedDiscriminatorModelNames || modelNames;
+    }
+
+    try {
+      addModelNamesToMap(model, map, available, modelNames, options, data, ret, doc, schemaOptions);
+    } catch (err) {
+      return err;
+    }
+  }
+  return map;
+
+  function _getModelNames(doc, schema, modelNameFromQuery, model) {
+    let modelNames;
+    let isRefPath = false;
+    let justOne = null;
+
+    const originalSchema = schema;
+    if (schema && schema.instance === 'Array') {
+      schema = schema.caster;
+    }
+    if (schema && schema.$isSchemaMap) {
+      schema = schema.$__schemaType;
+    }
+
+    const ref = schema && schema.options && schema.options.ref;
+    refPath = schema && schema.options && schema.options.refPath;
+    if (schema != null &&
+        schema[schemaMixedSymbol] &&
+        !ref &&
+        !refPath &&
+        !modelNameFromQuery) {
+      return { modelNames: null };
+    }
+
+    if (modelNameFromQuery) {
+      modelNames = [modelNameFromQuery]; // query options
+    } else if (refPath != null) {
+      if (typeof refPath === 'function') {
+        const subdocPath = options.path.slice(0, options.path.length - schema.path.length - 1);
+        const vals = mpath.get(subdocPath, doc, lookupLocalFields);
+        const subdocsBeingPopulated = Array.isArray(vals) ?
+          utils.array.flatten(vals) :
+          (vals ? [vals] : []);
+
+        modelNames = new Set();
+        for (const subdoc of subdocsBeingPopulated) {
+          refPath = refPath.call(subdoc, subdoc, options.path);
+          modelNamesFromRefPath(refPath, doc, options.path, modelSchema, options._queryProjection).
+            forEach(name => modelNames.add(name));
+        }
+        modelNames = Array.from(modelNames);
+      } else {
+        modelNames = modelNamesFromRefPath(refPath, doc, options.path, modelSchema, options._queryProjection);
+      }
+
+      isRefPath = true;
+    } else {
+      let ref;
+      let refPath;
+      let schemaForCurrentDoc;
+      let discriminatorValue;
+      let modelForCurrentDoc = model;
+      const discriminatorKey = model.schema.options.discriminatorKey;
+
+      if (!schema && discriminatorKey && (discriminatorValue = utils.getValue(discriminatorKey, doc))) {
+        // `modelNameForFind` is the discriminator value, so we might need
+        // find the discriminated model name
+        const discriminatorModel = getDiscriminatorByValue(model.discriminators, discriminatorValue) || model;
+        if (discriminatorModel != null) {
+          modelForCurrentDoc = discriminatorModel;
+        } else {
+          try {
+            modelForCurrentDoc = _getModelFromConn(model.db, discriminatorValue);
+          } catch (error) {
+            return error;
+          }
+        }
+
+        schemaForCurrentDoc = modelForCurrentDoc.schema._getSchema(options.path);
+
+        if (schemaForCurrentDoc && schemaForCurrentDoc.caster) {
+          schemaForCurrentDoc = schemaForCurrentDoc.caster;
+        }
+      } else {
+        schemaForCurrentDoc = schema;
+      }
+
+      if (originalSchema && originalSchema.path.endsWith('.$*')) {
+        justOne = !originalSchema.$isMongooseArray && !originalSchema._arrayPath;
+      } else if (schemaForCurrentDoc != null) {
+        justOne = !schemaForCurrentDoc.$isMongooseArray && !schemaForCurrentDoc._arrayPath;
+      }
+
+      if ((ref = get(schemaForCurrentDoc, 'options.ref')) != null) {
+        if (schemaForCurrentDoc != null &&
+            typeof ref === 'function' &&
+            options.path.endsWith('.' + schemaForCurrentDoc.path)) {
+          // Ensure correct context for ref functions: subdoc, not top-level doc. See gh-8469
+          modelNames = new Set();
+
+          const subdocPath = options.path.slice(0, options.path.length - schemaForCurrentDoc.path.length - 1);
+          const vals = mpath.get(subdocPath, doc, lookupLocalFields);
+          const subdocsBeingPopulated = Array.isArray(vals) ?
+            utils.array.flatten(vals) :
+            (vals ? [vals] : []);
+          for (const subdoc of subdocsBeingPopulated) {
+            modelNames.add(handleRefFunction(ref, subdoc));
+          }
+
+          if (subdocsBeingPopulated.length === 0) {
+            modelNames = [handleRefFunction(ref, doc)];
+          } else {
+            modelNames = Array.from(modelNames);
+          }
+        } else {
+          ref = handleRefFunction(ref, doc);
+          modelNames = [ref];
+        }
+      } else if ((schemaForCurrentDoc = get(schema, 'options.refPath')) != null) {
+        isRefPath = true;
+        if (typeof refPath === 'function') {
+          const subdocPath = options.path.slice(0, options.path.length - schemaForCurrentDoc.path.length - 1);
+          const vals = mpath.get(subdocPath, doc, lookupLocalFields);
+          const subdocsBeingPopulated = Array.isArray(vals) ?
+            utils.array.flatten(vals) :
+            (vals ? [vals] : []);
+
+          modelNames = new Set();
+          for (const subdoc of subdocsBeingPopulated) {
+            refPath = refPath.call(subdoc, subdoc, options.path);
+            modelNamesFromRefPath(refPath, doc, options.path, modelSchema, options._queryProjection).
+              forEach(name => modelNames.add(name));
+          }
+          modelNames = Array.from(modelNames);
+        } else {
+          modelNames = modelNamesFromRefPath(refPath, doc, options.path, modelSchema, options._queryProjection);
+        }
+      }
+    }
+
+    if (!modelNames) {
+      // `Model.populate()` on a POJO with no known local model. Default to using the `Model`
+      if (options._localModel == null) {
+        modelNames = [model.modelName];
+      } else {
+        return { modelNames: modelNames, justOne: justOne, isRefPath: isRefPath, refPath: refPath };
+      }
+    }
+
+    if (!Array.isArray(modelNames)) {
+      modelNames = [modelNames];
+    }
+
+    return { modelNames: modelNames, justOne: justOne, isRefPath: isRefPath, refPath: refPath };
+  }
+};
+
+/*!
+ * ignore
+ */
+
+function _virtualPopulate(model, docs, options, _virtualRes) {
+  const map = [];
+  const available = {};
+  const virtual = _virtualRes.virtual;
+
+  for (const doc of docs) {
+    let modelNames = null;
+    const data = {};
+
+    // localField and foreignField
+    let localField;
+    const virtualPrefix = _virtualRes.nestedSchemaPath ?
+      _virtualRes.nestedSchemaPath + '.' : '';
+    if (typeof options.localField === 'string') {
+      localField = options.localField;
+    } else if (typeof virtual.options.localField === 'function') {
+      localField = virtualPrefix + virtual.options.localField.call(doc, doc);
+    } else if (Array.isArray(virtual.options.localField)) {
+      localField = virtual.options.localField.map(field => virtualPrefix + field);
+    } else {
+      localField = virtualPrefix + virtual.options.localField;
+    }
+    data.count = virtual.options.count;
+
+    if (virtual.options.skip != null && !options.hasOwnProperty('skip')) {
+      options.skip = virtual.options.skip;
+    }
+    if (virtual.options.limit != null && !options.hasOwnProperty('limit')) {
+      options.limit = virtual.options.limit;
+    }
+    if (virtual.options.perDocumentLimit != null && !options.hasOwnProperty('perDocumentLimit')) {
+      options.perDocumentLimit = virtual.options.perDocumentLimit;
+    }
+    let foreignField = virtual.options.foreignField;
+
+    if (!localField || !foreignField) {
+      return new MongooseError(`Cannot populate virtual \`${options.path}\` on model \`${model.modelName}\`, because options \`localField\` and / or \`foreignField\` are missing`);
+    }
+
+    if (typeof localField === 'function') {
+      localField = localField.call(doc, doc);
+    }
+    if (typeof foreignField === 'function') {
+      foreignField = foreignField.call(doc, doc);
+    }
+
+    data.isRefPath = false;
+
+    // `justOne = null` means we don't know from the schema whether the end
+    // result should be an array or a single doc. This can result from
+    // populating a POJO using `Model.populate()`
+    let justOne = null;
+    if ('justOne' in options && options.justOne !== void 0) {
+      justOne = options.justOne;
+    }
+
+    modelNames = virtual._getModelNamesForPopulate(doc);
+    if (virtual.options.refPath) {
+      justOne = !!virtual.options.justOne;
+      data.isRefPath = true;
+    } else if (virtual.options.ref) {
+      justOne = !!virtual.options.justOne;
+    }
+
+    data.isVirtual = true;
+    data.virtual = virtual;
+    data.justOne = justOne;
+
+    // `match`
+    const baseMatch = get(data, 'virtual.options.match', null) ||
+      get(data, 'virtual.options.options.match', null);
+    let match = get(options, 'match', null) || baseMatch;
+
+    let hasMatchFunction = typeof match === 'function';
+    if (hasMatchFunction) {
+      match = match.call(doc, doc, data.virtual);
+    }
+
+    if (Array.isArray(localField) && Array.isArray(foreignField) && localField.length === foreignField.length) {
+      match = Object.assign({}, match);
+      for (let i = 1; i < localField.length; ++i) {
+        match[foreignField[i]] = convertTo_id(mpath.get(localField[i], doc, lookupLocalFields), model.schema);
+        hasMatchFunction = true;
+      }
+
+      localField = localField[0];
+      foreignField = foreignField[0];
+    }
+    data.localField = localField;
+    data.foreignField = foreignField;
+    data.match = match;
+    data.hasMatchFunction = hasMatchFunction;
+
+    throwOn$where(match);
+
+    // Get local fields
+    const ret = _getLocalFieldValues(doc, localField, model, options, virtual);
+
+    try {
+      addModelNamesToMap(model, map, available, modelNames, options, data, ret, doc);
+    } catch (err) {
+      return err;
+    }
+  }
+
+  return map;
+}
+
+/*!
+ * ignore
+ */
+
+function addModelNamesToMap(model, map, available, modelNames, options, data, ret, doc, schemaOptions, unpopulatedValue) {
+  // `PopulateOptions#connection`: if the model is passed as a string, the
+  // connection matters because different connections have different models.
+  const connection = options.connection != null ? options.connection : model.db;
+
+  unpopulatedValue = unpopulatedValue === void 0 ? ret : unpopulatedValue;
+  if (Array.isArray(unpopulatedValue)) {
+    unpopulatedValue = utils.cloneArrays(unpopulatedValue);
+  }
+
+  if (modelNames == null) {
+    return;
+  }
+
+  const flatModelNames = utils.array.flatten(modelNames);
+  let k = flatModelNames.length;
+  while (k--) {
+    let modelName = flatModelNames[k];
+    if (modelName == null) {
+      continue;
+    }
+
+    let Model;
+    if (options.model && options.model[modelSymbol]) {
+      Model = options.model;
+    } else if (modelName[modelSymbol]) {
+      Model = modelName;
+      modelName = Model.modelName;
+    } else {
+      try {
+        Model = _getModelFromConn(connection, modelName);
+      } catch (err) {
+        if (ret !== void 0) {
+          throw err;
+        }
+        Model = null;
+      }
+    }
+
+    let ids = ret;
+
+    const modelNamesForRefPath = data.modelNamesInOrder ? data.modelNamesInOrder : modelNames;
+    if (data.isRefPath && Array.isArray(ret) && ret.length === modelNamesForRefPath.length) {
+      ids = matchIdsToRefPaths(ret, modelNamesForRefPath, modelName);
+    }
+
+    const perDocumentLimit = options.perDocumentLimit == null ?
+      get(options, 'options.perDocumentLimit', null) :
+      options.perDocumentLimit;
+
+    if (!available[modelName] || perDocumentLimit != null) {
+      const currentOptions = {
+        model: Model
+      };
+      if (data.isVirtual && get(data.virtual, 'options.options')) {
+        currentOptions.options = clone(data.virtual.options.options);
+      } else if (schemaOptions != null) {
+        currentOptions.options = Object.assign({}, schemaOptions);
+      }
+      utils.merge(currentOptions, options);
+
+      // Used internally for checking what model was used to populate this
+      // path.
+      options[populateModelSymbol] = Model;
+      currentOptions[populateModelSymbol] = Model;
+      available[modelName] = {
+        model: Model,
+        options: currentOptions,
+        match: data.hasMatchFunction ? [data.match] : data.match,
+        docs: [doc],
+        ids: [ids],
+        allIds: [ret],
+        unpopulatedValues: [unpopulatedValue],
+        localField: new Set([data.localField]),
+        foreignField: new Set([data.foreignField]),
+        justOne: data.justOne,
+        isVirtual: data.isVirtual,
+        virtual: data.virtual,
+        count: data.count,
+        [populateModelSymbol]: Model
+      };
+      map.push(available[modelName]);
+    } else {
+      available[modelName].localField.add(data.localField);
+      available[modelName].foreignField.add(data.foreignField);
+      available[modelName].docs.push(doc);
+      available[modelName].ids.push(ids);
+      available[modelName].allIds.push(ret);
+      available[modelName].unpopulatedValues.push(unpopulatedValue);
+      if (data.hasMatchFunction) {
+        available[modelName].match.push(data.match);
+      }
+    }
+  }
+}
+
+function _getModelFromConn(conn, modelName) {
+  /* If this connection has a parent from `useDb()`, bubble up to parent's models */
+  if (conn.models[modelName] == null && conn._parent != null) {
+    return _getModelFromConn(conn._parent, modelName);
+  }
+
+  return conn.model(modelName);
+}
+
+function matchIdsToRefPaths(ids, refPaths, refPathToFind) {
+  if (!Array.isArray(refPaths)) {
+    return refPaths === refPathToFind
+      ? Array.isArray(ids)
+        ? utils.array.flatten(ids)
+        : [ids]
+      : [];
+  }
+  if (Array.isArray(ids) && Array.isArray(refPaths)) {
+    return ids.flatMap((id, index) => matchIdsToRefPaths(id, refPaths[index], refPathToFind));
+  }
+  return [];
+}
+
+/*!
+ * ignore
+ */
+
+function handleRefFunction(ref, doc) {
+  if (typeof ref === 'function' && !ref[modelSymbol]) {
+    return ref.call(doc, doc);
+  }
+  return ref;
+}
+
+/*!
+ * ignore
+ */
+
+function _getLocalFieldValues(doc, localField, model, options, virtual, schema) {
+  // Get Local fields
+  const localFieldPathType = model.schema._getPathType(localField);
+  const localFieldPath = localFieldPathType === 'real' ?
+    model.schema.path(localField) :
+    localFieldPathType.schema;
+  const localFieldGetters = localFieldPath && localFieldPath.getters ?
+    localFieldPath.getters : [];
+
+  localField = localFieldPath != null && localFieldPath.instance === 'Embedded' ? localField + '._id' : localField;
+
+  const _populateOptions = get(options, 'options', {});
+
+  const getters = 'getters' in _populateOptions ?
+    _populateOptions.getters :
+    get(virtual, 'options.getters', false);
+  if (localFieldGetters.length !== 0 && getters) {
+    const hydratedDoc = (doc.$__ != null) ? doc : model.hydrate(doc);
+    const localFieldValue = utils.getValue(localField, doc);
+    if (Array.isArray(localFieldValue)) {
+      const localFieldHydratedValue = utils.getValue(localField.split('.').slice(0, -1), hydratedDoc);
+      return localFieldValue.map((localFieldArrVal, localFieldArrIndex) =>
+        localFieldPath.applyGetters(localFieldArrVal, localFieldHydratedValue[localFieldArrIndex]));
+    } else {
+      return localFieldPath.applyGetters(localFieldValue, hydratedDoc);
+    }
+  } else {
+    return convertTo_id(mpath.get(localField, doc, lookupLocalFields), schema);
+  }
+}
+
+/**
+ * Retrieve the _id of `val` if a Document or Array of Documents.
+ *
+ * @param {Array|Document|Any} val
+ * @param {Schema} schema
+ * @return {Array|Document|Any}
+ * @api private
+ */
+
+function convertTo_id(val, schema) {
+  if (val != null && val.$__ != null) {
+    return val._doc._id;
+  }
+  if (val != null && val._id != null && (schema == null || !schema.$isSchemaMap)) {
+    return val._id;
+  }
+
+  if (Array.isArray(val)) {
+    const rawVal = val.__array != null ? val.__array : val;
+    for (let i = 0; i < rawVal.length; ++i) {
+      if (rawVal[i] != null && rawVal[i].$__ != null) {
+        rawVal[i] = rawVal[i]._doc._id;
+      }
+    }
+    if (utils.isMongooseArray(val) && val.$schema()) {
+      return val.$schema()._castForPopulate(val, val.$parent());
+    }
+
+    return [].concat(val);
+  }
+
+  // `populate('map')` may be an object if populating on a doc that hasn't
+  // been hydrated yet
+  if (getConstructorName(val) === 'Object' &&
+      // The intent here is we should only flatten the object if we expect
+      // to get a Map in the end. Avoid doing this for mixed types.
+      (schema == null || schema[schemaMixedSymbol] == null)) {
+    const ret = [];
+    for (const key of Object.keys(val)) {
+      ret.push(val[key]);
+    }
+    return ret;
+  }
+  // If doc has already been hydrated, e.g. `doc.populate('map')`
+  // then `val` will already be a map
+  if (val instanceof Map) {
+    return Array.from(val.values());
+  }
+
+  return val;
+}
+
+/*!
+ * ignore
+ */
+
+function _findRefPathForDiscriminators(doc, modelSchema, data, options, normalizedRefPath, ret) {
+  // Re: gh-8452. Embedded discriminators may not have `refPath`, so clear
+  // out embedded discriminator docs that don't have a `refPath` on the
+  // populated path.
+  if (!data.isRefPath || normalizedRefPath == null) {
+    return;
+  }
+
+  const pieces = normalizedRefPath.split('.');
+  let cur = '';
+  let modelNames = void 0;
+  for (let i = 0; i < pieces.length; ++i) {
+    const piece = pieces[i];
+    cur = cur + (cur.length === 0 ? '' : '.') + piece;
+    const schematype = modelSchema.path(cur);
+    if (schematype != null &&
+        schematype.$isMongooseArray &&
+        schematype.caster.discriminators != null &&
+        Object.keys(schematype.caster.discriminators).length !== 0) {
+      const subdocs = utils.getValue(cur, doc);
+      const remnant = options.path.substring(cur.length + 1);
+      const discriminatorKey = schematype.caster.schema.options.discriminatorKey;
+      modelNames = [];
+      for (const subdoc of subdocs) {
+        const discriminatorName = utils.getValue(discriminatorKey, subdoc);
+        const discriminator = schematype.caster.discriminators[discriminatorName];
+        const discriminatorSchema = discriminator && discriminator.schema;
+        if (discriminatorSchema == null) {
+          continue;
+        }
+        const _path = discriminatorSchema.path(remnant);
+        if (_path == null || _path.options.refPath == null) {
+          const docValue = utils.getValue(data.localField.substring(cur.length + 1), subdoc);
+          ret.forEach((v, i) => {
+            if (v === docValue) {
+              ret[i] = SkipPopulateValue(v);
+            }
+          });
+          continue;
+        }
+        const modelName = utils.getValue(pieces.slice(i + 1).join('.'), subdoc);
+        modelNames.push(modelName);
+      }
+    }
+  }
+
+  return modelNames;
+}
+
+/**
+ * Throw an error if there are any $where keys
+ */
+
+function throwOn$where(match) {
+  if (match == null) {
+    return;
+  }
+  if (typeof match !== 'object') {
+    return;
+  }
+  for (const key of Object.keys(match)) {
+    if (key === '$where') {
+      throw new MongooseError('Cannot use $where filter with populate() match');
+    }
+    if (match[key] != null && typeof match[key] === 'object') {
+      throwOn$where(match[key]);
+    }
+  }
+}