perf: optimize virtual fields that reference ID (#12159)

This PR optimizes the new virtual fields with relationships feature
https://github.com/payloadcms/payload/pull/11805 when the path
references the ID field, for example:
```
{
  name: 'postCategoryID',
  type: 'number',
  virtual: 'post.category.id',
},
```

Previously, we did additional population of `category`, which is
unnecessary as we can always grab the ID from the `category` value
itself. One less querying step.

packages/payload/src/fields/hooks/afterRead/virtualFieldPopulationPromise.ts

@@ -85,6 +85,11 @@ export const virtualFieldPopulationPromise = async ({
       docID = currentValue
     }
 
+    if (segments[0] === 'id' && segments.length === 0) {
+      siblingDoc[name] = docID
+      return
+    }
+
     if (typeof docID !== 'string' && typeof docID !== 'number') {
       return
     }

test/database/config.ts

@@ -471,6 +471,16 @@ export default buildConfigWithDefaults({
           type: 'text',
           virtual: 'post.category.title',
         },
+        {
+          name: 'postCategoryID',
+          type: 'json',
+          virtual: 'post.category.id',
+        },
+        {
+          name: 'postID',
+          type: 'json',
+          virtual: 'post.id',
+        },
         {
           name: 'postLocalized',
           type: 'text',
@@ -481,6 +491,16 @@ export default buildConfigWithDefaults({
           type: 'relationship',
           relationTo: 'posts',
         },
+        {
+          name: 'customID',
+          type: 'relationship',
+          relationTo: 'custom-ids',
+        },
+        {
+          name: 'customIDValue',
+          type: 'text',
+          virtual: 'customID.id',
+        },
       ],
       versions: { drafts: true },
     },

test/database/int.spec.ts

@@ -1993,11 +1993,63 @@ describe('database', () => {
         collection: 'virtual-relations',
         depth: 0,
         where: { id: { equals: id } },
-        draft: true,
       })
       expect(draft.docs[0]?.postTitle).toBe('my-title')
     })
 
+    it('should allow virtual field as reference to ID', async () => {
+      const post = await payload.create({ collection: 'posts', data: { title: 'my-title' } })
+      const { id } = await payload.create({
+        collection: 'virtual-relations',
+        depth: 0,
+        data: { post: post.id },
+      })
+
+      const docDepth2 = await payload.findByID({ collection: 'virtual-relations', id })
+      expect(docDepth2.postID).toBe(post.id)
+      const docDepth0 = await payload.findByID({ collection: 'virtual-relations', id, depth: 0 })
+      expect(docDepth0.postID).toBe(post.id)
+    })
+
+    it('should allow virtual field as reference to custom ID', async () => {
+      const customID = await payload.create({ collection: 'custom-ids', data: {} })
+      const { id } = await payload.create({
+        collection: 'virtual-relations',
+        depth: 0,
+        data: { customID: customID.id },
+      })
+
+      const docDepth2 = await payload.findByID({ collection: 'virtual-relations', id })
+      expect(docDepth2.customIDValue).toBe(customID.id)
+      const docDepth0 = await payload.findByID({
+        collection: 'virtual-relations',
+        id,
+        depth: 0,
+      })
+      expect(docDepth0.customIDValue).toBe(customID.id)
+    })
+
+    it('should allow deep virtual field as reference to ID', async () => {
+      const category = await payload.create({
+        collection: 'categories',
+        data: { title: 'category-3' },
+      })
+      const post = await payload.create({
+        collection: 'posts',
+        data: { category: category.id, title: 'my-title-3' },
+      })
+      const { id } = await payload.create({
+        collection: 'virtual-relations',
+        depth: 0,
+        data: { post: post.id },
+      })
+
+      const docDepth2 = await payload.findByID({ collection: 'virtual-relations', id })
+      expect(docDepth2.postCategoryID).toBe(category.id)
+      const docDepth0 = await payload.findByID({ collection: 'virtual-relations', id, depth: 0 })
+      expect(docDepth0.postCategoryID).toBe(category.id)
+    })
+
     it('should allow virtual field with reference localized', async () => {
       const post = await payload.create({
         collection: 'posts',

test/database/payload-types.ts

@@ -373,8 +373,39 @@ export interface VirtualRelation {
   id: string;
   postTitle?: string | null;
   postCategoryTitle?: string | null;
+  postCategoryID?:
+    | {
+        [k: string]: unknown;
+      }
+    | unknown[]
+    | string
+    | number
+    | boolean
+    | null;
+  postID?:
+    | {
+        [k: string]: unknown;
+      }
+    | unknown[]
+    | string
+    | number
+    | boolean
+    | null;
   postLocalized?: string | null;
   post?: (string | null) | Post;
+  customID?: (string | null) | CustomId;
+  customIDValue?: string | null;
+  updatedAt: string;
+  createdAt: string;
+  _status?: ('draft' | 'published') | null;
+}
+/**
+ * This interface was referenced by `Config`'s JSON-Schema
+ * via the `definition` "custom-ids".
+ */
+export interface CustomId {
+  id: string;
+  title?: string | null;
   updatedAt: string;
   createdAt: string;
   _status?: ('draft' | 'published') | null;
@@ -398,17 +429,6 @@ export interface FieldsPersistance {
   updatedAt: string;
   createdAt: string;
 }
-/**
- * This interface was referenced by `Config`'s JSON-Schema
- * via the `definition` "custom-ids".
- */
-export interface CustomId {
-  id: string;
-  title?: string | null;
-  updatedAt: string;
-  createdAt: string;
-  _status?: ('draft' | 'published') | null;
-}
 /**
  * This interface was referenced by `Config`'s JSON-Schema
  * via the `definition` "fake-custom-ids".
@@ -807,8 +827,12 @@ export interface PlacesSelect<T extends boolean = true> {
 export interface VirtualRelationsSelect<T extends boolean = true> {
   postTitle?: T;
   postCategoryTitle?: T;
+  postCategoryID?: T;
+  postID?: T;
   postLocalized?: T;
   post?: T;
+  customID?: T;
+  customIDValue?: T;
   updatedAt?: T;
   createdAt?: T;
   _status?: T;