From 53c8da1b57bb19603ac8131dbca26023ed0001c7 Mon Sep 17 00:00:00 2001
From: Valeri Karpov <val@karpov.io>
Date: Tue, 10 Sep 2024 11:06:58 -0400
Subject: [PATCH] feat(SchemaType): add getEmbeddedSchemaType() method to
 SchemaTypes

Fix #8389
---
 lib/schemaType.js         | 18 ++++++++++++++++++
 test/schematype.test.js   |  9 +++++++++
 test/types/schema.test.ts |  7 +++++++
 types/schematypes.d.ts    |  3 +++
 4 files changed, 37 insertions(+)

diff --git a/lib/schemaType.js b/lib/schemaType.js
index f95ecbb3226..53cc8caedaf 100644
--- a/lib/schemaType.js
+++ b/lib/schemaType.js
@@ -1724,6 +1724,24 @@ SchemaType.prototype.clone = function() {
   return schematype;
 };
 
+/**
+ * Returns the embedded schema type, if any. For arrays, document arrays, and maps, `getEmbeddedSchemaType()`
+ * returns the schema type of the array's elements (or map's elements). For other types, `getEmbeddedSchemaType()`
+ * returns `undefined`.
+ *
+ * #### Example:
+ *
+ *     const schema = new Schema({ name: String, tags: [String] });
+ *     schema.path('name').getEmbeddedSchemaType(); // undefined
+ *     schema.path('tags').getEmbeddedSchemaType(); // SchemaString { path: 'tags', ... }
+ *
+ * @returns {SchemaType} embedded schematype
+ */
+
+SchemaType.prototype.getEmbeddedSchemaType = function getEmbeddedSchemaType() {
+  return this.$embeddedSchemaType;
+};
+
 /*!
  * Module exports.
  */
diff --git a/test/schematype.test.js b/test/schematype.test.js
index ad8367d0f61..725e21966a4 100644
--- a/test/schematype.test.js
+++ b/test/schematype.test.js
@@ -315,4 +315,13 @@ describe('schematype', function() {
       /password must be at least six characters/
     );
   });
+
+  it('supports getEmbeddedSchemaType() (gh-8389)', function() {
+    const schema = new Schema({ name: String, tags: [String] });
+    assert.strictEqual(schema.path('name').getEmbeddedSchemaType(), undefined);
+    const schemaType = schema.path('tags').getEmbeddedSchemaType();
+    assert.ok(schemaType);
+    assert.equal(schemaType.instance, 'String');
+    assert.equal(schemaType.path, 'tags');
+  });
 });
diff --git a/test/types/schema.test.ts b/test/types/schema.test.ts
index 04828bc4f17..a2164ddaa2e 100644
--- a/test/types/schema.test.ts
+++ b/test/types/schema.test.ts
@@ -1634,3 +1634,10 @@ function gh14825() {
   type SchemaType = InferSchemaType<typeof schema>;
   expectAssignable<User>({} as SchemaType);
 }
+
+function gh8389() {
+  const schema = new Schema({ name: String, tags: [String] });
+
+  expectAssignable<SchemaType<any> | undefined>(schema.path('name').getEmbeddedSchemaType());
+  expectAssignable<SchemaType<any> | undefined>(schema.path('tags').getEmbeddedSchemaType());
+}
diff --git a/types/schematypes.d.ts b/types/schematypes.d.ts
index e8a0ecffdf0..1e270733e48 100644
--- a/types/schematypes.d.ts
+++ b/types/schematypes.d.ts
@@ -229,6 +229,9 @@ declare module 'mongoose' {
     /** Adds a getter to this schematype. */
     get(fn: Function): this;
 
+    /** Gets this SchemaType's embedded SchemaType, if any  */
+    getEmbeddedSchemaType<T = any, DocType = any>(): SchemaType<T, DocType> | undefined;
+
     /**
      * Defines this path as immutable. Mongoose prevents you from changing
      * immutable paths unless the parent document has [`isNew: true`](/docs/api/document.html#document_Document-isNew).