feat: support hasMany virtual relationship fields (#13879)

This PR adds support for the following configuration:
```ts
const config = {
  collections: [
    {
      slug: 'categories',
      fields: [
        {
          name: 'title',
          type: 'text',
        },
      ],
    },
    {
      slug: 'posts',
      fields: [
        {
          name: 'title',
          type: 'text',
        },
        {
          name: 'categories',
          type: 'relationship',
          relationTo: 'categories',
          hasMany: true,
        },
      ],
    },
    {
      slug: 'examples',
      fields: [
        {
          name: 'postCategoriesTitles',
          type: 'text',
          virtual: 'post.categories.title',
          // hasMany: true - added automatically during the sanitization
        },
        {
          type: 'relationship',
          relationTo: 'posts',
          name: 'post',
        },
        {
          name: 'postsTitles',
          type: 'text',
          virtual: 'posts.title',
          // hasMany: true - added automatically during the sanitization
        },
        {
          type: 'relationship',
          relationTo: 'posts',
          name: 'posts',
          hasMany: true,
        },
      ],
    },
  ],
}
```

In the result:
`postsTitles` - will be always populated with an array of posts titles.
`postCategoriesTitles` - will be always populated with an array of the
categories titles that are related to this post

The virtual `text` field is sanitizated to `hasMany: true`
automatically, but you can specify that manually as well.

test/database/getConfig.ts

@@ -607,6 +607,16 @@ export const getConfig: () => Partial<Config> = () => ({
           type: 'text',
           virtual: 'post.title',
         },
+        {
+          name: 'postsTitles',
+          type: 'text',
+          virtual: 'posts.title',
+        },
+        {
+          name: 'postCategoriesTitles',
+          type: 'text',
+          virtual: 'post.categories.title',
+        },
         {
           name: 'postTitleHidden',
           type: 'text',
@@ -643,6 +653,12 @@ export const getConfig: () => Partial<Config> = () => ({
           type: 'relationship',
           relationTo: 'posts',
         },
+        {
+          name: 'posts',
+          type: 'relationship',
+          relationTo: 'posts',
+          hasMany: true,
+        },
         {
           name: 'customID',
           type: 'relationship',

test/database/int.spec.ts

@@ -2988,6 +2988,58 @@ describe('database', () => {
       })
       expect(docs).toHaveLength(1)
     })
+
+    it('should automatically add hasMany: true to a virtual field that references a hasMany relationship', () => {
+      const field = payload.collections['virtual-relations'].config.fields.find(
+        // eslint-disable-next-line jest/no-conditional-in-test
+        (each) => 'name' in each && each.name === 'postsTitles',
+      )!
+
+      // eslint-disable-next-line jest/no-conditional-in-test
+      expect('hasMany' in field && field.hasMany).toBe(true)
+    })
+
+    it('should the value populate with hasMany: true relationship field', async () => {
+      await payload.delete({ collection: 'categories', where: {} })
+      await payload.delete({ collection: 'posts', where: {} })
+      await payload.delete({ collection: 'virtual-relations', where: {} })
+
+      const post1 = await payload.create({ collection: 'posts', data: { title: 'post 1' } })
+      const post2 = await payload.create({ collection: 'posts', data: { title: 'post 2' } })
+
+      const res = await payload.create({
+        collection: 'virtual-relations',
+        depth: 0,
+        data: { posts: [post1.id, post2.id] },
+      })
+      expect(res.postsTitles).toEqual(['post 1', 'post 2'])
+    })
+
+    it('should the value populate with nested hasMany: true relationship field', async () => {
+      await payload.delete({ collection: 'categories', where: {} })
+      await payload.delete({ collection: 'posts', where: {} })
+      await payload.delete({ collection: 'virtual-relations', where: {} })
+
+      const category_1 = await payload.create({
+        collection: 'categories',
+        data: { title: 'category 1' },
+      })
+      const category_2 = await payload.create({
+        collection: 'categories',
+        data: { title: 'category 2' },
+      })
+      const post1 = await payload.create({
+        collection: 'posts',
+        data: { title: 'post 1', categories: [category_1.id, category_2.id] },
+      })
+
+      const res = await payload.create({
+        collection: 'virtual-relations',
+        depth: 0,
+        data: { post: post1.id },
+      })
+      expect(res.postCategoriesTitles).toEqual(['category 1', 'category 2'])
+    })
   })
 
   it('should convert numbers to text', async () => {

test/database/payload-types.ts

@@ -327,7 +327,7 @@ export interface RelationA {
     root: {
       type: string;
       children: {
-        type: string;
+        type: any;
         version: number;
         [k: string]: unknown;
       }[];
@@ -353,7 +353,7 @@ export interface RelationB {
     root: {
       type: string;
       children: {
-        type: string;
+        type: any;
         version: number;
         [k: string]: unknown;
       }[];
@@ -450,6 +450,8 @@ export interface Place {
 export interface VirtualRelation {
   id: string;
   postTitle?: string | null;
+  postsTitles?: string[] | null;
+  postCategoriesTitles?: string[] | null;
   postTitleHidden?: string | null;
   postCategoryTitle?: string | null;
   postCategoryID?:
@@ -473,6 +475,7 @@ export interface VirtualRelation {
     | null;
   postLocalized?: string | null;
   post?: (string | null) | Post;
+  posts?: (string | Post)[] | null;
   customID?: (string | null) | CustomId;
   customIDValue?: string | null;
   updatedAt: string;
@@ -1046,6 +1049,8 @@ export interface PlacesSelect<T extends boolean = true> {
  */
 export interface VirtualRelationsSelect<T extends boolean = true> {
   postTitle?: T;
+  postsTitles?: T;
+  postCategoriesTitles?: T;
   postTitleHidden?: T;
   postCategoryTitle?: T;
   postCategoryID?: T;
@@ -1053,6 +1058,7 @@ export interface VirtualRelationsSelect<T extends boolean = true> {
   postID?: T;
   postLocalized?: T;
   post?: T;
+  posts?: T;
   customID?: T;
   customIDValue?: T;
   updatedAt?: T;