Linking collections through the API

Support
1

So, I’m trying to link two entries through the API.
And I’m a bit lost
I have a parents collections and a comments collection.
In the parents collection I have a comments field with the type collectionlink
And in the commentscollection I have a parent filed with the type collectionlink
I can POST new entries in both collections, but I’m stuck when it comes to linking a comment to a parent.

Any suggestions on how to link them up?

Great product!

2

Bump
I hope my question is clear.
So far vanilla JS and using the API
I have two linked collections. I can post to the parent collection and the child collection individually, but I cannot figure out how to, from a HTTP request, tell the child that it belongs to a certain parent, or tell the parent that there’s a new child
Any hints/suggestions/documentation?
Thanks

3

In the beginning it is a chicken-egg problem, right? In order to link a comment item to a parent item you need to know the parent-items _id value. Which you only get after you created the parent-item.
And to link the parent-item to the comment-item you need to know the comment-items’ _id, again only available after the comment-items’ creation.

So the process seems to be

  • POST create-parent-item without comment link
  • now parent-item._id is known, e.g. 6128aa4e3630618af4000188
  • POST create-comment-item with
{
  "parentLink": {
      "_id": "6128aa4e3630618af4000188",
      "link": "parents",
      "display": "entry 1"
  }
  ...
}
  • now comment-item._id is known, e.g. 6123b44c6138326b83000331
  • GET parent-item current object to have the latest version of it
  • extract and extend commentsLink array by new reference to new comment-item (I assume this is a 1:n multilink relationship)
{
  "commentsLink": [
      {
          "_id": "6123b44c6138326b83000331",
          "link": "comments",
          "display": "comment 1"
      }
  ],
  ...
}
  • POST update-parent-item /api/collections/parents/save
// param "data"
{
  _id: "6128aa4e3630618af4000188",
  "commentsLink": [
      {
          "_id": "6123b44c6138326b83000331",
          "link": "comments",
          "display": "comment 1"
      }
  ]
}
  • done.

BUT be aware, that due to the asynchronous nature of those request this scenario bears a high risk of race conditions where 2 comments at the same time get not properly linked, because they update the same parent item at the same time.

A cleaner solution would be to only save the parents-link in the comment-item when creating the new comment-item and then have a custom script triggered on-comment-item-save to update the links in the related parent-item.
And in order to avoid repeating the race-condition-out-of-sync (only on a smaller scale) issue you might not only want to just add the current comment but “all lately (within the last seconds) created, related and not-linked-in-parent-yet” comments.

And maybe I overshot here.
But my answer to your question

You do this by having the collectionlink fields data added into your HTTP POST requests.
First into the comment-item:

  • POST /api/collections/comments/save + data=NEW_COMMENTS_OBJECT_WITH_COLLECTION_LINK_FIELD_DATA

And then as an additional update to the related parents object

  • POST /api/collections/comments/save + data={_id: PARENTS_ITEM_ID*, commentsLink: [UPDATED_COLLECTIONLINK_DATA_ARRAY]}

*) having the _id key set in a collections-save call triggers an “update” for which it is not necessary to post the whole object but is sufficient to only post the to-be-updated fields

4

Thanks Abernh, roughly where I’m at right now, so great that you can sort of verify I’m not totally off. I guess I was hoping for a “push method” of some sort, to only add stuff to the collection array, without having to send the entire array of children again (in order to avoid the race condition)
Still not sure if I should link stuff both ways or just from child to parent or parent to child, but getting there. Thanks!