Why does step 2 in migrating files to media try to insert to the nid from the source and not the target?

Question

I am doing a migration as per this example https://www.drupal.org/project/migrate_file_to_media/issues/3118471. Migration and step 1 work fine, I get this error when running step 2. I also tried running the migration with an --update flag (drush mim migd8_blog_media_step2 --update) and get the same error . its trying to do an insert instead of an update. And its trying to insert into the source nid, not the target nid.

Drupal\Core\Database\IntegrityConstraintViolationException: SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'title'[error]cannot be null: INSERT INTO {​​​​​node_field_data}​​​​​ (nid, vid, type, langcode, status, uid, title, created, changed, promote, sticky, default_langcode, revision_translation_affected, publish_on, unpublish_on) VALUES (:db_insert_placeholder_0, :db_insert_placeholder_1, :db_insert_placeholder_2, :db_insert_placeholder_3, :db_insert_placeholder_4, :db_insert_placeholder_5, :db_insert_placeholder_6, :db_insert_placeholder_7, :db_insert_placeholder_8, :db_insert_placeholder_9, :db_insert_placeholder_10, :db_insert_placeholder_11, :db_insert_placeholder_12, :db_insert_placeholder_13, :db_insert_placeholder_14); Array ( [:db_insert_placeholder_0] => 22610

This is the id of the source node, not the target The migration file I am using contains the following lines.

# This migration links the newly created media entities with entity reference field on the target bundle.
id: migd8_blog_media_step2
label: blog Media Mapping
source:
  key: migrate
  plugin: d7_node
  node_type: blog_entry
destination:
  plugin: entity:node
  default_bundle: blog
process: 
  nid: nid
  changed: changed
  field_files:
    plugin: file_id_lookup
    source: field_main_image
    migration: migd8_blog_media_step1
    no_stub: true
migration_dependencies:
  optional:
  - migd8_node_blog
  - migd8_blog_media_step1

this is my step 1:

# File to Media Migration configuration for blog Media migration

id: migd8_blog_media_step1
label: blog Media Step 1
migration_group: cncs
source:
  key: migrate
  plugin: media_entity_generator_d7
  entity_type: node
  bundle: blog_entry
  langcode: und
  d7_file_url: 'https://www.nationalservice.gov/sites/default/files/'
  #d7_file_url: 'public://'
  field_names:
    - field_main_image

destination:
  plugin: entity:media

process:
    
  bundle:
    plugin: default_value
    default_value: image

  # Using the alt tag if available, else the file name.
  name:
    plugin: media_name
    source: file_name

  # This process plugin will skip the whole row if a existing media is found.
  existing_media_file:
    plugin: check_media_duplicate
    source: target_id

  # This process plugin will skip the whole row if a duplicate image is found.
  unique_file_id:
    plugin: check_duplicate
    source: target_id
    
  # Map the field 
  
  
  field_media_image/alt: alt
  field_media_image/title: title
  field_media_image/target_id:
    plugin: media_file_copy
    move: FALSE
    reuse: TRUE
    path: 'public://images/'
    source: file_path

  langcode: langcode
   
  uid:
    plugin: default_value
    default_value: 1
`

here is my main migration yml :

id: 

migd8_node_blog
label: Custom node migration from Drupal 7
migration_group: cncs
deriver: Drupal\node\Plugin\migrate\D7NodeDeriver
dependencies:
  enforced:
    module:
      - migd8_node_blog_node
source:
 plugin: migd8_node_blog_node # use custom source plugin
 node_type: blog_entry
destination:
  plugin: entity:node
  bundle: blog
process:
  'path/pathauto':
    plugin: default_value
    default_value: 0 # Disable pathauto.
  'path/alias': alias
  type: 
    plugin: default_value
    default_value: blog
  status: status
  uid: 
    plugin: default_value
    default_value: 1
  title: title
  langcode:
    plugin: static_map
    bypass: true
    source: language
    map:
      und: en
  created: created
  changed: changed
  promote: promote
  field_blog_tags:
    plugin: migration_lookup
    source: field_blog_tags
    migration: migrate_taxonomy
  sticky: sticky
  body:
      plugin: sub_process
      source: body
      process:
        value: value
        summary: summary
        format:
          plugin: default_value
          default_value: full_html
  field_blog_author: field_blog_author        
  field_blog_post_date_: 
    plugin: iterator
    source: field_blog_post_date_
    process:
      value:
        plugin: substr
        source: value
        start: 0
        length: 10

I realize its looking for the source nid in this query , not the target nid Drupal\Core\Database\IntegrityConstraintViolationException: SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'title'[error]cannot be null: INSERT INTO {​​​​​node_field_data}​​​​​ (nid, vid, type, langcode, status, uid, title, created, changed, promote, sticky, default_langcode, revision_translation_affected, publish_on, unpublish_on) VALUES (:db_insert_placeholder_0, :db_insert_placeholder_1, :db_insert_placeholder_2, :db_insert_placeholder_3, :db_insert_placeholder_4, :db_insert_placeholder_5, :db_insert_placeholder_6, :db_insert_placeholder_7, :db_insert_placeholder_8, :db_insert_placeholder_9, :db_insert_placeholder_10, :db_insert_placeholder_11, :db_insert_placeholder_12, :db_insert_placeholder_13, :db_insert_placeholder_14); Array ( [:db_insert_placeholder_0] => 22610 22610 is the node id in the source. in the target its a totally different nid

Answer 1

As the Migrating nodes doc shows, it needs to be:

destination:
  plugin: entity:node
  default_bundle: blog

Answer 2

i imported the new nodes with the same nid as the old ones using

nid: nid 

in the process that fixed the problem!