Example migration using a parent child relationship based on parents using a base ID (e.g. 'did0001') and children with a padded integer appended with a hyphen (e.g. 'did0001-001' and 'did0001-002').

migrate_plus.migration.node.yml

langcode: en
status: true
dependencies: {  }
id: node
label: 'Nodes for paged content'
source:
  plugin: csv
  path: modules/my_module/metadata/nodes.csv
  delimiter: ','
  header_row_count: 1
  constants:
    uid: 1
    parent_model: 'Paged Content'
    child_model: 'Page'
  keys:
    - digital_id
  column_names:
    -
      digital_id: 'Digital Identifier'
    -
      title: Title
    -
      description: Description
    -
      part_of: 'ArchivesSpace Source Reference ID'
process:
  uid: constants/uid
  field_digital_id: digital_id
  title:
    plugin: callback
    callable: utf8_encode
    source: title
  body/format: 
    plugin: default_value
    default_value: full_html
  body/value: 
    plugin: callback
    callable: utf8_encode
    source: description
  temp_archival_object_parent:
    -
      plugin: skip_on_empty
      method: process
      source: part_of
    -
      plugin: entity_lookup
      value_key: field_as_ref_id
      bundle_key: type
      bundle: archival_object
      entity_type: node
      ignore_case: true
  temp_digital_object_parent:
    -
      plugin: skip_on_regex
      method: process
      not_equals: true
      value: '|-|'
      source: digital_id
    -
      plugin: str_replace
      regex: true
      search: '/-.*/i'
      replace: ''
    -
      plugin: entity_lookup
      value_key: field_digital_id
      bundle_key: type
      bundle: dc_object
      entity_type: node
      ignore_case: true
  field_member_of:
    -
      plugin: get
      source:
        - '@temp_archival_object_parent'
        - '@temp_digital_object_parent'
    -
      plugin: flatten
  field_weight:
    -
      plugin: skip_on_regex
      method: process
      not_equals: true
      value: '|-|'
      source: digital_id
    -
      plugin: str_replace
      regex: true
      search: '/.*-/i'
      replace: ''
    -
      plugin: callback
      callable: intval
  temp_parent_model:
    -
      plugin: skip_on_regex
      method: process
      not_equals: true
      value: '|-|'
      source: digital_id
    -
      plugin: entity_lookup
      source: constants/parent_model
      value_key: name
      bundle_key: vid
      bundle: islandora_models
      entity_type: taxonomy_term
      ignore_case: true
  temp_parent_model:
    -
      plugin: skip_on_regex
      method: process
      not_equals: false
      value: '|-|'
      source: digital_id
    -
      plugin: entity_lookup
      source: constants/child_model
      value_key: name
      bundle_key: vid
      bundle: islandora_models
      entity_type: taxonomy_term
      ignore_case: true
  field_model:
    -
      plugin: get
      source:
        - '@temp_parent_model'
        - '@temp_child_model'
    -
      plugin: flatten
destination:
  plugin: 'entity:node'
  default_bundle: islandora_object
migration_dependencies: null