From be67d0f9242ace96cac3583e1617b4d879b86ca5 Mon Sep 17 00:00:00 2001
From: Valeri Karpov <val@karpov.io>
Date: Sat, 6 May 2023 21:34:34 -0400
Subject: [PATCH] fix(document): handle set() from top-level underneath a map
 of mixed

Re: #13327
---
 lib/document.js       | 34 ++++++++++++++++++++++++----------
 test/document.test.js | 18 ++++++++++++++++++
 2 files changed, 42 insertions(+), 10 deletions(-)

diff --git a/lib/document.js b/lib/document.js
index cdc6dc3212f..7ce10c71f7c 100644
--- a/lib/document.js
+++ b/lib/document.js
@@ -1250,6 +1250,11 @@ Document.prototype.$set = function $set(path, val, type, options) {
         // allow changes to sub paths of mixed types
         mixed = true;
         break;
+      } else if (schema.$isSchemaMap && schema.$__schemaType instanceof MixedSchema && i < parts.length - 1) {
+        // Map of mixed and not the last element in the path resolves to mixed
+        mixed = true;
+        schema = schema.$__schemaType;
+        break;
       }
     }
 
@@ -1688,17 +1693,26 @@ Document.prototype.$__set = function(pathToMark, path, options, constructing, pa
         obj[parts[i]] = val;
       }
     } else {
-      if (utils.isPOJO(obj[parts[i]])) {
-        obj = obj[parts[i]];
-      } else if (obj[parts[i]] && obj[parts[i]] instanceof Embedded) {
-        obj = obj[parts[i]];
-      } else if (obj[parts[i]] && !Array.isArray(obj[parts[i]]) && obj[parts[i]].$isSingleNested) {
-        obj = obj[parts[i]]._doc;
-      } else if (obj[parts[i]] && Array.isArray(obj[parts[i]])) {
-        obj = obj[parts[i]];
+      const isMap = obj instanceof Map;
+      let value = isMap ? obj.get(parts[i]) : obj[parts[i]];
+      if (utils.isPOJO(value)) {
+        obj = value;
+      } else if (value && value instanceof Embedded) {
+        obj = value;
+      } else if (value && !Array.isArray(value) && value.$isSingleNested) {
+        obj = value._doc;
+      } else if (value && Array.isArray(value)) {
+        obj = value;
+      } else if (value == null) {
+        value = {};
+        if (isMap) {
+          obj.set(parts[i], value);
+        } else {
+          obj[parts[i]] = value;
+        }
+        obj = value;
       } else {
-        obj[parts[i]] = obj[parts[i]] || {};
-        obj = obj[parts[i]];
+        obj = value;
       }
     }
   }
diff --git a/test/document.test.js b/test/document.test.js
index c941c64b3b4..12d23812a54 100644
--- a/test/document.test.js
+++ b/test/document.test.js
@@ -12094,6 +12094,24 @@ describe('document', function() {
     const fromDb = await Test.findById(x._id).lean();
     assert.equal(fromDb.d.x.y, 1);
   });
+
+  it('can set() from top-level on path underneath map of mixed (gh-13327)', async function() {
+    const testSchema = new Schema({
+      c: {
+        type: Map,
+        of: 'Mixed'
+      }
+    });
+    const Test = db.model('Test', testSchema);
+
+    const x = new Test();
+    x.set('c.x.y', 1);
+    assert.strictEqual(x.get('c.x.y'), 1);
+    await x.save();
+
+    const fromDb = await Test.findById(x._id).lean();
+    assert.equal(fromDb.c.x.y, 1);
+  });
 });
 
 describe('Check if instance function that is supplied in schema option is availabe', function() {