From a81211de24c045a29b1df9ffba288608ee57f32b Mon Sep 17 00:00:00 2001
From: Valeri Karpov <val@karpov.io>
Date: Mon, 21 Oct 2019 12:20:43 -0400
Subject: [PATCH] fix(populate): add document array subpaths to parent doc
 `populated()` when calling `DocumentArray#push()`

Fix #8247
---
 lib/document.js         |  7 +------
 lib/types/core_array.js | 21 ++++++++++++++++++++-
 2 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/lib/document.js b/lib/document.js
index e108d55679c..23c30db1ce0 100644
--- a/lib/document.js
+++ b/lib/document.js
@@ -1130,12 +1130,7 @@ Document.prototype.$set = function $set(path, val, type, options) {
 
     let didPopulate = false;
     if (refMatches && val instanceof Document) {
-      if (this.ownerDocument) {
-        this.ownerDocument().populated(this.$__fullPath(path),
-          val._id, { [populateModelSymbol]: val.constructor });
-      } else {
-        this.populated(path, val._id, { [populateModelSymbol]: val.constructor });
-      }
+      this.populated(path, val._id, { [populateModelSymbol]: val.constructor });
       didPopulate = true;
     }
 
diff --git a/lib/types/core_array.js b/lib/types/core_array.js
index 9f0aa9f5f25..92121d9a523 100644
--- a/lib/types/core_array.js
+++ b/lib/types/core_array.js
@@ -628,11 +628,30 @@ class CoreMongooseArray extends Array {
 
     _checkManualPopulation(this, arguments);
 
+    const parent = this[arrayParentSymbol];
     let values = [].map.call(arguments, this._mapCast, this);
-    values = this[arraySchemaSymbol].applySetters(values, this[arrayParentSymbol], undefined,
+    values = this[arraySchemaSymbol].applySetters(values, parent, undefined,
       undefined, { skipDocumentArrayCast: true });
     const ret = [].push.apply(this, values);
 
+    // If this is a document array, each element may contain single
+    // populated paths, so we need to modify the top-level document's
+    // populated cache. See gh-8247.
+    if (this.isMongooseDocumentArray && parent.$__.populated != null) {
+      const populatedPaths = Object.keys(parent.$__.populated).
+        filter(p => p.startsWith(this[arrayPathSymbol] + '.'));
+
+      for (const path of populatedPaths) {
+        const remnant = path.slice((this[arrayPathSymbol] + '.').length);
+        if (!Array.isArray(parent.$__.populated[path].value)) {
+          continue;
+        }
+        for (const val of values) {
+          parent.$__.populated[path].value.push(val.populated(remnant));
+        }
+      }
+    }
+
     this._registerAtomic('$push', values);
     this._markModified();
     return ret;