fix(db-postgres): querying on array wtihin a relationship field (#8152)

## Description

Fixes https://github.com/payloadcms/payload/issues/6037

- [x] I have read and understand the
[CONTRIBUTING.md](https://github.com/payloadcms/payload/blob/main/CONTRIBUTING.md)
document in this repository.

## Type of change

<!-- Please delete options that are not relevant. -->

- [x] Bug fix (non-breaking change which fixes an issue)

## Checklist:

- [x] I have added tests that prove my fix is effective or that my
feature works
- [x] Existing test suite passes locally with my changes

test/relationships/config.ts

@@ -290,6 +290,31 @@ export default buildConfigWithDefaults({
         },
       ],
     },
+    {
+      slug: 'pages',
+      fields: [
+        {
+          type: 'array',
+          name: 'menu',
+          fields: [
+            {
+              name: 'label',
+              type: 'text',
+            },
+          ],
+        },
+      ],
+    },
+    {
+      slug: 'rels-to-pages',
+      fields: [
+        {
+          name: 'page',
+          type: 'relationship',
+          relationTo: 'pages',
+        },
+      ],
+    },
   ],
   onInit: async (payload) => {
     await payload.create({

test/relationships/int.spec.ts

@@ -10,6 +10,7 @@ import type {
   CustomIdNumberRelation,
   CustomIdRelation,
   Director,
+  Page,
   Post,
   PostsLocalized,
   Relation,
@@ -676,6 +677,37 @@ describe('Relationships', () => {
         expect(query.docs).toHaveLength(1)
         expect(query.docs[0].id).toStrictEqual(firstLevelID)
       })
+
+      it('should allow querying within array nesting', async () => {
+        const page = await payload.create({
+          collection: 'pages',
+          data: {
+            menu: [
+              {
+                label: 'hello',
+              },
+            ],
+          },
+        })
+
+        const rel = await payload.create({ collection: 'rels-to-pages', data: { page: page.id } })
+
+        const resEquals = await payload.find({
+          collection: 'rels-to-pages',
+          where: { 'page.menu.label': { equals: 'hello' } },
+        })
+
+        expect(resEquals.totalDocs).toBe(1)
+        expect(resEquals.docs[0].id).toBe(rel.id)
+
+        const resIn = await payload.find({
+          collection: 'rels-to-pages',
+          where: { 'page.menu.label': { in: ['hello'] } },
+        })
+
+        expect(resIn.totalDocs).toBe(1)
+        expect(resIn.docs[0].id).toBe(rel.id)
+      })
     })
 
     describe('Nested Querying Separate Collections', () => {

test/relationships/payload-types.ts

@@ -24,6 +24,8 @@ export interface Config {
     movieReviews: MovieReview;
     'polymorphic-relationships': PolymorphicRelationship;
     tree: Tree;
+    pages: Page;
+    'rels-to-pages': RelsToPage;
     users: User;
     'payload-preferences': PayloadPreference;
     'payload-migrations': PayloadMigration;
@@ -224,6 +226,31 @@ export interface Tree {
   updatedAt: string;
   createdAt: string;
 }
+/**
+ * This interface was referenced by `Config`'s JSON-Schema
+ * via the `definition` "pages".
+ */
+export interface Page {
+  id: string;
+  menu?:
+    | {
+        label?: string | null;
+        id?: string | null;
+      }[]
+    | null;
+  updatedAt: string;
+  createdAt: string;
+}
+/**
+ * This interface was referenced by `Config`'s JSON-Schema
+ * via the `definition` "rels-to-pages".
+ */
+export interface RelsToPage {
+  id: string;
+  page?: (string | null) | Page;
+  updatedAt: string;
+  createdAt: string;
+}
 /**
  * This interface was referenced by `Config`'s JSON-Schema
  * via the `definition` "payload-preferences".