fix(types): correct return value for Model.exists()

Fix #12094

Author: vkarpov15

test/types/models.test.ts

@@ -345,3 +345,16 @@ function gh12100() {
 
   expectType<string>(obj._id);
 })();
+
+(async function gh12094() {
+  const userSchema = new Schema({
+    name: { type: String, required: true },
+    email: { type: String, required: true },
+    avatar: String
+  });
+
+  const User = model('User', userSchema);
+
+  const doc = await User.exists({ name: 'Bill' }).orFail();
+  expectType<Types.ObjectId>(doc._id);
+})();

types/models.d.ts

@@ -306,11 +306,11 @@ declare module 'mongoose' {
     estimatedDocumentCount(options?: QueryOptions<T>, callback?: Callback<number>): QueryWithHelpers<number, HydratedDocument<T, TMethodsAndOverrides, TVirtuals>, TQueryHelpers, T>;
 
     /**
-   * Returns a document with its `_id` if at least one document exists in the database that matches
-   * the given `filter`, and `null` otherwise.
-   */
-    exists(filter: FilterQuery<T>, callback: Callback<Pick<Document<T>, '_id'> | null>): QueryWithHelpers<Pick<Document<T>, '_id'> | null, HydratedDocument<T, TMethodsAndOverrides, TVirtuals>, TQueryHelpers, T>;
-    exists(filter: FilterQuery<T>): QueryWithHelpers<Pick<Document<T>, '_id'> | null, HydratedDocument<T, TMethodsAndOverrides, TVirtuals>, TQueryHelpers, T>;
+     * Returns a document with its `_id` if at least one document exists in the database that matches
+     * the given `filter`, and `null` otherwise.
+     */
+    exists(filter: FilterQuery<T>, callback: Callback<{ _id: InferId<T> } | null>): QueryWithHelpers<Pick<Document<T>, '_id'> | null, HydratedDocument<T, TMethodsAndOverrides, TVirtuals>, TQueryHelpers, T>;
+    exists(filter: FilterQuery<T>): QueryWithHelpers<{ _id: InferId<T> } | null, HydratedDocument<T, TMethodsAndOverrides, TVirtuals>, TQueryHelpers, T>;
 
     /** Creates a `find` query: gets a list of documents that match `filter`. */
     find<ResultDoc = HydratedDocument<T, TMethodsAndOverrides, TVirtuals>>(