some progress

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

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+'use strict';
+
+const MongooseError = require('../../error/mongooseError');
+const isPathExcluded = require('../projection/isPathExcluded');
+const lookupLocalFields = require('./lookupLocalFields');
+const mpath = require('mpath');
+const util = require('util');
+const utils = require('../../utils');
+
+const hasNumericPropRE = /(\.\d+$|\.\d+\.)/g;
+
+module.exports = function modelNamesFromRefPath(refPath, doc, populatedPath, modelSchema, queryProjection) {
+  if (refPath == null) {
+    return [];
+  }
+
+  if (typeof refPath === 'string' && queryProjection != null && isPathExcluded(queryProjection, refPath)) {
+    throw new MongooseError('refPath `' + refPath + '` must not be excluded in projection, got ' +
+      util.inspect(queryProjection));
+  }
+
+  // If populated path has numerics, the end `refPath` should too. For example,
+  // if populating `a.0.b` instead of `a.b` and `b` has `refPath = a.c`, we
+  // should return `a.0.c` for the refPath.
+
+  if (hasNumericPropRE.test(populatedPath)) {
+    const chunks = populatedPath.split(hasNumericPropRE);
+
+    if (chunks[chunks.length - 1] === '') {
+      throw new Error('Can\'t populate individual element in an array');
+    }
+
+    let _refPath = '';
+    let _remaining = refPath;
+    // 2nd, 4th, etc. will be numeric props. For example: `[ 'a', '.0.', 'b' ]`
+    for (let i = 0; i < chunks.length; i += 2) {
+      const chunk = chunks[i];
+      if (_remaining.startsWith(chunk + '.')) {
+        _refPath += _remaining.substring(0, chunk.length) + chunks[i + 1];
+        _remaining = _remaining.substring(chunk.length + 1);
+      } else if (i === chunks.length - 1) {
+        _refPath += _remaining;
+        _remaining = '';
+        break;
+      } else {
+        throw new Error('Could not normalize ref path, chunk ' + chunk + ' not in populated path');
+      }
+    }
+
+    const refValue = mpath.get(_refPath, doc, lookupLocalFields);
+    let modelNames = Array.isArray(refValue) ? refValue : [refValue];
+    modelNames = utils.array.flatten(modelNames);
+    return modelNames;
+  }
+
+  const refValue = mpath.get(refPath, doc, lookupLocalFields);
+
+  let modelNames;
+  if (modelSchema != null && modelSchema.virtuals.hasOwnProperty(refPath)) {
+    modelNames = [modelSchema.virtuals[refPath].applyGetters(void 0, doc)];
+  } else {
+    modelNames = Array.isArray(refValue) ? refValue : [refValue];
+  }
+
+  modelNames = utils.array.flatten(modelNames);
+
+  return modelNames;
+};