HOWTO: Create menu_link_content items with a parent

While working on a site I changed from using Default Content's drush commands to export the entities to doing them by hand based upon examples previously created. This worked well up until I was trying to set the parent on menu_link_content entities. After some testing I finally worked out how to do it so wanted to document it here.

This is the parent item that will have child element(s) later:

_meta:
  version: '1.0'
  entity_type: menu_link_content
  uuid: 2d0659d1-ba09-4bca-9adc-9833d484590a
  bundle: main
  default_langcode: en
default:
  enabled:
    -
      value: true
  title:
    -
      value: "The parent"
  menu_name:
    -
      value: main
  link:
    -
      uri: 'internal:/some/thing'
      title: ''
  external:
    -
      value: false
  rediscover:
    -
      value: false
  weight:
    -
      value: -10
  expanded:
    -
      value: false
  revision_translation_affected:
    -
      value: true

This is the child element:

_meta:
  version: '1.0'
  entity_type: menu_link_content
  uuid: e412fa5d-1926-428d-8926-45f257d9c92e
  bundle: main
  default_langcode: en
  depends:
    2d0659d1-ba09-4bca-9adc-9833d484590a: menu_link_content
default:
  enabled:
    -
      value: true
  title:
    -
      value: "Child page"
  menu_name:
    -
      value: main
  link:
    -
      uri: 'internal:/over/there'
      title: ''
  external:
    -
      value: false
  rediscover:
    -
      value: false
  weight:
    -
      value: -100
  expanded:
    -
      value: false
  revision_translation_affected:
    -
      value: true
  parent:
    -
      value: 'menu_link_content:2d0659d1-ba09-4bca-9adc-9833d484590a'

The important pieces of the child are:

• The parent's UUID must be listed as a "depends" line to make sure the parent is created first.
• The "parent" value is set to "menu_link_content:[PARENTUUID]" i.e. the entity type name of "menu_link_content" followed by the parent item's UUID. This matches what is stored as the "parent" value of the {menu_link_content_data} table, and also the "parent" value of the {menu_tree} table.

I tried using the parent item's ID, its UUID, using "target_id" as the key, using "parent_id" as the attribute, lots of different options, but this was the correct combination in the end.