Allow populate to accept field.name

[yulolimum]

Hello!

There are times when a collection (CollectionA) might have multiple relationship fields to the same (CollectionB). For example (this is a stupid example but bear with me):

• Users
  • posts_i_authored -> Posts
  • posts_im_modering -> Posts
  • posts_i_deleted -> Posts

When using populate, right now that affects all CollectionA relationship fields that point to CollectionB.

payload.find({ 
  collection: 'users', 
  populate: { 
    posts: {
      slug: true
    }
 }
})

What I am proposing is to be able to populate based on field name as well:

payload.find({ 
  collection: 'users', 
  populate: { 
    // base collection setting
    posts: {
      slug: true
    },
    // field based settings
    posts_i_authored: {
      createdAt: true
    },
    posts_i_deleted: {
      deletion_reason: true
    }
 }
})

This example would produce a response like so:

{docs: [
  ...userdata,
  posts_i_authored: [
    {id: uuid, slug: "slug", createdAt: timestamp}
  ],
  posts_i_deleted: [
    {id: uuid, slug: "slug", deletion_reason: ""}
  ],
  posts_im_modering: [
    {id: uuid, ...defaultPopulate},
  ],
])

---

I created a reproduction and patch as an example:

1. clone repo

     git clone [email protected]:yulolimum/tmp-payload-populate-w-field-name-repro.git

2. install deps

   yarn

3. start dev server

   yarn dev

4. authenticate at https://localhost:3000/admin

   username: [email protected] password: Password1!

5. go to: http://localhost:3000/users-w-posts-n-myposts-w-default-populate

   You will see both posts and myPosts with defaultPopulate (slug only)

6. go to: http://localhost:3000/users-w-posts-w-populate

   You will see both posts and myPosts with custom collection-level populate (title only)

7. go to http://localhost:3000/users-w-myposts-w-populate

   You WILL see both posts and myPosts with custom collection-level populate (title).
   With the proposed change, you SHOULD see posts with "title" but myPosts with both "title" and "content" (collection-level & field-level merged).

8. apply patch

rm -rf .next && npx patch-package --use-npm && yarn dev

9. go to http://localhost:3000/users-w-myposts-w-populate

   You will see

   • posts with "title" (collection-level) populate applied
   • myPosts with "title" and "description" (collection-level and field-level) populate applied

---

For visibility, this is the patch that attempts this functionality, although more changes are necessary to satisfy TS:

diff --git a/node_modules/payload/dist/fields/hooks/afterRead/relationshipPopulationPromise.js b/node_modules/payload/dist/fields/hooks/afterRead/relationshipPopulationPromise.js
index d853052..336c9ae 100644
--- a/node_modules/payload/dist/fields/hooks/afterRead/relationshipPopulationPromise.js
+++ b/node_modules/payload/dist/fields/hooks/afterRead/relationshipPopulationPromise.js
@@ -17,19 +17,26 @@ const populate = async ({ currentDepth, data, dataReference, depth, draft, fallb
             id = id.toString();
         }
         if (shouldPopulate) {
-            relationshipValue = await req.payloadDataLoader.load(createDataloaderCacheKey({
-                collectionSlug: relatedCollection.config.slug,
-                currentDepth: currentDepth + 1,
-                depth,
-                docID: id,
-                draft,
-                fallbackLocale,
-                locale,
-                overrideAccess,
-                select: populateArg?.[relatedCollection.config.slug] ?? relatedCollection.config.defaultPopulate,
-                showHiddenFields,
-                transactionID: req.transactionID
-            }));
+            const populateOverride =
+                populateArg?.[relatedCollection.config.slug] || populateArg?.[field.name]
+                ? { ...populateArg?.[relatedCollection.config.slug], ...populateArg?.[field.name] }
+                : undefined
+        
+            relationshipValue = await req.payloadDataLoader.load(
+                createDataloaderCacheKey({
+                    collectionSlug: relatedCollection.config.slug,
+                    currentDepth: currentDepth + 1,
+                    depth,
+                    docID: id,
+                    draft,
+                    fallbackLocale,
+                    locale,
+                    overrideAccess,
+                    select: populateOverride ?? relatedCollection.config.defaultPopulate,
+                    showHiddenFields,
+                    transactionID: req.transactionID,
+                })
+            )
         }
         if (!relationshipValue) {
             // ids are visible regardless of access controls