From 9856e4705927539ae5b8663f56ad28f772491e4c Mon Sep 17 00:00:00 2001
From: Shashank Kaul <kaulshashank96@gmail.com>
Date: Thu, 7 Sep 2023 21:35:41 +0530
Subject: [PATCH] feat: Safer types for `Model.distinct` and `Query.distinct`.

---
 test/types/queries.test.ts | 5 +++--
 types/models.d.ts          | 7 +++++--
 types/query.d.ts           | 6 +++---
 3 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/test/types/queries.test.ts b/test/types/queries.test.ts
index efca12618a5..2b6175dfd30 100644
--- a/test/types/queries.test.ts
+++ b/test/types/queries.test.ts
@@ -295,8 +295,9 @@ async function gh11306(): Promise<void> {
   // 3. Create a Model.
   const MyModel = model<User>('User', schema);
 
-  expectType<any[]>(await MyModel.distinct('name'));
-  expectType<string[]>(await MyModel.distinct<string>('name'));
+  expectType<unknown[]>(await MyModel.distinct('notThereInSchema'));
+  expectType<string[]>(await MyModel.distinct('name'));
+  expectType<number[]>(await MyModel.distinct<'overrideTest', number>('overrideTest'));
 }
 
 function autoTypedQuery() {
diff --git a/types/models.d.ts b/types/models.d.ts
index 2b0a5989445..1d001640565 100644
--- a/types/models.d.ts
+++ b/types/models.d.ts
@@ -443,8 +443,11 @@ declare module 'mongoose' {
     translateAliases(raw: any): any;
 
     /** Creates a `distinct` query: returns the distinct values of the given `field` that match `filter`. */
-    distinct<ReturnType = any>(field: string, filter?: FilterQuery<TRawDocType>): QueryWithHelpers<
-      Array<ReturnType>,
+    distinct<DocKey extends string, ResultType = unknown>(
+      field: DocKey,
+      filter?: FilterQuery<TRawDocType>
+    ): QueryWithHelpers<
+      Array<DocKey extends keyof TRawDocType ? TRawDocType[DocKey] : ResultType>,
       THydratedDocumentType,
       TQueryHelpers,
       TRawDocType,
diff --git a/types/query.d.ts b/types/query.d.ts
index 3963481a20b..2fb346fdd5c 100644
--- a/types/query.d.ts
+++ b/types/query.d.ts
@@ -317,10 +317,10 @@ declare module 'mongoose' {
     deleteOne(): QueryWithHelpers<any, DocType, THelpers, RawDocType, 'deleteOne'>;
 
     /** Creates a `distinct` query: returns the distinct values of the given `field` that match `filter`. */
-    distinct<ReturnType = any>(
-      field: string,
+    distinct<DocKey extends string, ResultType = unknown>(
+      field: DocKey,
       filter?: FilterQuery<DocType>
-    ): QueryWithHelpers<Array<ReturnType>, DocType, THelpers, RawDocType, 'distinct'>;
+    ): QueryWithHelpers<Array<DocKey extends keyof DocType ? DocType[DocKey] : ResultType>, DocType, THelpers, RawDocType, 'distinct'>;
 
     /** Specifies a `$elemMatch` query condition. When called with one argument, the most recent path passed to `where()` is used. */
     elemMatch<K = string>(path: K, val: any): this;