fix(populate): handle deselected foreign field with `perDocumentLimit…

…` and multiple documents

Fix #9175

lib/helpers/populate/removeDeselectedForeignField.js

@@ -0,0 +1,31 @@
+'use strict';
+
+const get = require('../get');
+const mpath = require('mpath');
+const parseProjection = require('../projection/parseProjection');
+
+/*!
+ * ignore
+ */
+
+module.exports = function removeDeselectedForeignField(foreignFields, options, docs) {
+  const projection = parseProjection(get(options, 'select', null), true) ||
+    parseProjection(get(options, 'options.select', null), true);
+
+  if (projection == null) {
+    return;
+  }
+  for (const foreignField of foreignFields) {
+    if (!projection.hasOwnProperty('-' + foreignField)) {
+      continue;
+    }
+
+    for (const val of docs) {
+      if (val.$__ != null) {
+        mpath.unset(foreignField, val._doc);
+      } else {
+        mpath.unset(foreignField, val);
+      }
+    }
+  }
+}

lib/model.js

@@ -34,20 +34,19 @@ const castBulkWrite = require('./helpers/model/castBulkWrite');
 const getDefaultBulkwriteResult = require('./helpers/getDefaultBulkwriteResult');
 const discriminator = require('./helpers/model/discriminator');
 const each = require('./helpers/each');
+const get = require('./helpers/get');
 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 get = require('./helpers/get');
 const leanPopulateMap = require('./helpers/populate/leanPopulateMap');
 const modifiedPaths = require('./helpers/update/modifiedPaths');
-const mpath = require('mpath');
 const parallelLimit = require('./helpers/parallelLimit');
 const promiseOrCallback = require('./helpers/promiseOrCallback');
-const parseProjection = require('./helpers/projection/parseProjection');
+const removeDeselectedForeignField = require('./helpers/populate/removeDeselectedForeignField');
 const util = require('util');
 const utils = require('./utils');
 
@@ -4465,6 +4464,10 @@ function populate(model, docs, options, callback) {
       const assignmentOpts = arr[3];
       _assign(model, vals, mod, assignmentOpts);
     }
+
+    for (const arr of params) {
+      removeDeselectedForeignField(arr[0].foreignField, arr[0].options, vals);
+    }
     callback();
   }
 }
@@ -4531,8 +4534,6 @@ function _assign(model, vals, mod, assignmentOpts) {
   const justOne = mod.justOne;
   let _val;
   const lean = get(options, 'options.lean', false);
-  const projection = parseProjection(get(options, 'select', null), true) ||
-    parseProjection(get(options, 'options.select', null), true);
   const len = vals.length;
   const rawOrder = {};
   const rawDocs = {};
@@ -4602,16 +4603,6 @@ function _assign(model, vals, mod, assignmentOpts) {
       } else {
         val.$__.wasPopulated = true;
       }
-
-      // gh-8460: if user used `-foreignField`, assume this means they
-      // want the foreign field unset even if it isn't excluded in the query.
-      if (projection != null && projection.hasOwnProperty('-' + foreignField)) {
-        if (val.$__ != null) {
-          val.set(foreignField, void 0);
-        } else {
-          mpath.unset(foreignField, val);
-        }
-      }
     }
   }