Avoid storing a separate entry in schema subpaths for every element in an array

lib/schema.js

@@ -1017,7 +1017,7 @@ Schema.prototype.path = function(path, obj) {
 
     // subpaths?
     return /\.\d+\.?.*$/.test(path)
-      ? getPositionalPath(this, path)
+      ? getPositionalPath(this, path, cleanPath)
       : undefined;
   }
 
@@ -1634,7 +1634,7 @@ Schema.prototype.pathType = function(path) {
   }
 
   if (/\.\d+\.|\.\d+$/.test(path)) {
-    return getPositionalPathType(this, path);
+    return getPositionalPathType(this, path, cleanPath);
   }
   return 'adhocOrUndefined';
 };
@@ -1678,7 +1678,7 @@ Schema.prototype.setupTimestamp = function(timestamps) {
  * @api private
  */
 
-function getPositionalPathType(self, path) {
+function getPositionalPathType(self, path, cleanPath) {
   const subpaths = path.split(/\.(\d+)\.|\.(\d+)$/).filter(Boolean);
   if (subpaths.length < 2) {
     return self.paths.hasOwnProperty(subpaths[0]) ?
@@ -1729,7 +1729,7 @@ function getPositionalPathType(self, path) {
     val = val.schema.path(subpath);
   }
 
-  self.subpaths[path] = val;
+  self.subpaths[cleanPath] = val;
   if (val) {
     return 'real';
   }
@@ -1744,9 +1744,9 @@ function getPositionalPathType(self, path) {
  * ignore
  */
 
-function getPositionalPath(self, path) {
-  getPositionalPathType(self, path);
-  return self.subpaths[path];
+function getPositionalPath(self, path, cleanPath) {
+  getPositionalPathType(self, path, cleanPath);
+  return self.subpaths[cleanPath];
 }
 
 /**
@@ -2638,6 +2638,9 @@ Schema.prototype._getSchema = function(path) {
       // Re: gh-5628, because `schema.path()` doesn't take $ into account.
       parts[i] = '0';
     }
+    if (/^\d+$/.test(parts[i])) {
+      parts[i] = '$';
+    }
   }
   return search(parts, _this);
 };

test/document.test.js

@@ -12520,6 +12520,36 @@ describe('document', function() {
     await doc.save();
     assert.strictEqual(attachmentSchemaPreValidateCalls, 1);
   });
+
+  it('avoids creating separate subpaths entry for every element in array (gh-13874)', async function() {
+    const tradeSchema = new mongoose.Schema({ tradeId: Number, content: String });
+
+    const testSchema = new mongoose.Schema(
+      {
+        userId: Number,
+        tradeMap: {
+          type: Map,
+          of: tradeSchema
+        }
+      }
+    );
+
+    const TestModel = db.model('Test', testSchema);
+
+
+    const userId = 100;
+    const user = await TestModel.create({ userId, tradeMap: new Map() });
+
+    // add subDoc
+    for (let id = 1; id <= 10; id++) {
+      const trade = { tradeId: id, content: 'test' };
+      user.tradeMap.set(trade.tradeId.toString(), trade);
+    }
+    await user.save();
+    await TestModel.deleteOne({ userId });
+
+    assert.equal(Object.keys(TestModel.schema.subpaths).length, 3);
+  });
 });
 
 describe('Check if instance function that is supplied in schema option is availabe', function() {