How do I migrate file uploads?

Question

I'm working on a custom migration from Drupal 6 to Drupal 8. Some of the content types have a field used for file attachments (field_attachments).

When I run the migration that connects the files to the nodes, I get this error.

SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'title' cannot be null: INSERT INTO {node_field_data} (nid, vid, type, langcode, status, uid, title, created, changed, promote, sticky, default_langcode, revision_translation_affected) 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); Array ( [:db_insert_placeholder_0] => 2064 [:db_insert_placeholder_1] => 3019 [:db_insert_placeholder_2] => forum [:db_insert_placeholder_3] => en [:db_insert_placeholder_4] => 1 [:db_insert_placeholder_5] => 0 [:db_insert_placeholder_6] => [:db_insert_placeholder_7] => 1558576761 [:db_insert_placeholder_8] => 1558576761 [:db_insert_placeholder_9] => 0 [:db_insert_placeholder_10] => 0 [:db_insert_placeholder_11] => 1 [:db_insert_placeholder_12] => 1 ) (/app/web/core/lib/Drupal/Core/Entity/Sql/SqlContentEntityStorage.php:847)

The migrate_plus.migration.custom_upload.yml file for the migration contains the following lines.

langcode: en
status: true
dependencies: {  }
id: custom_upload
class: Drupal\migrate\Plugin\Migration
field_plugin_method: alterFieldInstanceMigration
cck_plugin_method: null
migration_tags:
  - 'Drupal 6'
  - Content
migration_group: custom
label: 'File uploads'
source:
  plugin: d6_upload
process:
  nid:
    -
      plugin: get
      source: nid
  vid:
    -
      plugin: get
      source: vid
  langcode:
    -
      plugin: user_langcode
      source: language
      fallback_to_site_default: true
  type:
    -
      plugin: get
      source: type
  field_attachments:
    -
      plugin: sub_process
      source: upload
      process:
        target_id:
          plugin: migration_lookup
          migration: custom_file
          source: fid
        display:
          plugin: default_value
          default_value: 1
        description: description
destination:
  plugin: 'entity:node'
migration_dependencies:
  required:
    - custom_file
    - custom_article
    - custom_forum

From the error message, it appears that Drupal is trying to create a node; even though, I'm actually running the custom_upload migration after I ran the migration of all nodes.

I have migrated the nodes and the files already and I can see all the nodes in the database as well as the files in their directory and the database.

What am I missing?

Answer 1

Your custom_upload migration is trying to create nodes; the custom_upload migration is taking a d6_upload source plugin:

source:
  plugin: d6_upload

...and mapping it to a node:entity destination plugin:

destination:
  plugin: 'entity:node'

Since the d6_upload source doesn't have a title field to map to the node:entity field in the process definition of your migration, the migration fails as it tries to insert a titleless node.

You need update your node migration. If your node/file migrations are working, the node migration should have a process.field_attachments yml property to map field_attachments.target_id to the fid property from your custom_file migration.

Answer 2

Every content type migration creates its own mapping table.

I got a clue from how the taxonomy terms are migrated. The trick was to tell Drupal where to look for the nid.

I replaced:

process:
  nid:
    -
      plugin: get
      source: nid
  vid:
    -
      plugin: get
      source: vid

with...

process:
  nid:
    -
      plugin: migration_lookup
      migration:
        - custom_article
        - custom_forum
      source: nid
    -
      plugin: skip_on_empty
      method: row

... and now it works.

By listing the internal names of my two content types, Drupal was able to figure out what node mapping table should be used.

Note that I removed the vid: block with the replacement. I'm not importing node revisions and therefore, I'm not expecting that this will affect anything in my case.