Issue Summary

Assuming that there is a hierarchy of custom contents

page:
- custom content parent (ac:app:parent)
  - custom content child (ac:app:child)
    - custom content grandchild (ac:app:child)

 grandchildren are not returned when calling a Get Content REST API with children expansion or Get Content Children By Type for the child custom content.

Steps to Reproduce

Having the following custom content types configured (in atlassian-connect.json)

"customContent": [
    {
        "key": "parent",
        "name": {
            "value": "Parent"
        },
        "apiSupport": {
           "supportedContainerTypes": [
               "page"
           ],
           "supportedChildTypes": [
               "ac:my-app:child"
           ],
           // ...
        }
    },
    {
        "key": "child",
        "name": {
            "value": "child"
        },
        "apiSupport": {
            "supportedContainerTypes": [
                "ac:my-app:parent",
                "ac:my-app:child"
            ],
            "supportedChildTypes": [
                "ac:my-app:child"
            ],
            // ...
        }
    }
]

1. Create a hierarchy of custom content as shown in issue summary. It can be done through a Create Content REST API (POST to rest/api/content) using the following request bodies. You have to use undocumented container parameter to specify a container page for parent custom content, container parent custom content for child custom component and so on.

   {
       "type": "ac:my-app:parent",
       "title": "Custom Component Parent",
       "container": {
           "type": "page"
           "id": "<page-id>"
       },
       "space":{
           "key": "MYSPACEKEY"
       },
       "body":{
           "storage": {
               "value": "Custom Component Parent body",
               "representation": "storage"
           }
       }
   }
   

   {
       "type": "ac:my-app:child",
       "title": "Custom Component Child",
       "container": {
           "type": "ac:my-app:parent"
           "id": "<parent-custom-content-id>"
       },
       "space":{
           "key": "MYSPACEKEY"
       },
       "body":{
           "storage": {
               "value": "Custom Component Child body",
               "representation": "storage"
           }
       }
   }

1. Use GET request to Get Content (with expand) and Get Content Children By Type REST APIs to get a list of grandchildren

   {{baseurl}}/rest/api/content/<child-id>?expand=children.ac__my_app__child

   {{baseurl}}/rest/api/content/<child-id>/child/ac:my-app:child

Expected Results

Both APIs return a list of grandchildren.

Actual Results

The returned list is empty

Workaround

Look up grandchild content id in the CONTENT table in the database

select contentid, title from content where contenttype = 'CUSTOM' and pageid = '<child-id>';

Get the returned content id and use Get Content REST API to get the grandchild content

{{baseurl}}/rest/api/content/<grandchildchild-id>