fix(schema): handle maps of maps

Fix #10644

Author: vkarpov15

lib/schema.js

@@ -681,21 +681,9 @@ Schema.prototype.path = function(path, obj) {
     // The '$' is to imply this path should never be stored in MongoDB so we
     // can easily build a regexp out of this path, and '*' to imply "any key."
     const mapPath = path + '.$*';
-    let _mapType = { type: {} };
-    if (utils.hasUserDefinedProperty(obj, 'of')) {
-      const isInlineSchema = utils.isPOJO(obj.of) &&
-        Object.keys(obj.of).length > 0 &&
-        !utils.hasUserDefinedProperty(obj.of, this.options.typeKey);
-      _mapType = isInlineSchema ? new Schema(obj.of) : obj.of;
-    }
-    if (utils.hasUserDefinedProperty(obj, 'ref')) {
-      _mapType = { type: _mapType, ref: obj.ref };
-    }
 
-    this.paths[mapPath] = this.interpretAsType(mapPath,
-      _mapType, this.options);
+    this.paths[mapPath] = schemaType.$__schemaType;
     this.mapPaths.push(this.paths[mapPath]);
-    schemaType.$__schemaType = this.paths[mapPath];
   }
 
   if (schemaType.$isSingleNested) {
@@ -1032,9 +1020,41 @@ Schema.prototype.interpretAsType = function(path, obj, options) {
       'http://bit.ly/mongoose-schematypes for a list of valid schema types.');
   }
 
-  return new MongooseTypes[name](path, obj);
+  const schemaType = new MongooseTypes[name](path, obj);
+
+  if (schemaType.$isSchemaMap) {
+    createMapNestedSchemaType(this, schemaType, path, obj, options);
+  }
+
+  return schemaType;
 };
 
+/*!
+ * ignore
+ */
+
+function createMapNestedSchemaType(schema, schemaType, path, obj, options) {
+  const mapPath = path + '.$*';
+  let _mapType = { type: {} };
+  if (utils.hasUserDefinedProperty(obj, 'of')) {
+    const isInlineSchema = utils.isPOJO(obj.of) &&
+      Object.keys(obj.of).length > 0 &&
+      !utils.hasUserDefinedProperty(obj.of, schema.options.typeKey);
+    if (isInlineSchema) {
+      _mapType = { [schema.options.typeKey]: new Schema(obj.of) };
+    } else if (utils.isPOJO(obj.of)) {
+      _mapType = Object.assign({}, obj.of);
+    } else {
+      _mapType = { [schema.options.typeKey]: obj.of };
+    }
+
+    if (utils.hasUserDefinedProperty(obj, 'ref')) {
+      _mapType.ref = obj.ref;
+    }
+  }
+  schemaType.$__schemaType = schema.interpretAsType(mapPath, _mapType, options);
+}
+
 /**
  * Iterates the schemas paths similar to Array#forEach.
  *