Drupal 8 migrate plugin - explanation needed - drupal

Question

I want to migrate data from custom table to book content type, however I have no idea how to achieve that.
This is my config\install\migrate.migration.book_content.yml file:
id: book_content
label: Book content
migration_group: example
source:
plugin: book_content
target: db_migration
destination:
plugin: entity:node
process:
type:
plugin: default_value
default_value: article
title: title
uid:
plugin: default_value
default_value: 1
sticky:
plugin: default_value
default_value: 0
status:
plugin: default_value
default_value: 1
'body/value': content
'body/summary': excerpt
'body/format':
plugin: default_value
default_value: full_html
# Use of the migration process plugin.
# That will use the id map of the specified migration
# to retrieve the corresponding id ('source' parameter) in the destination database.
field_description:
plugin: migration
source: body
src\Plugin\migrate\source\BookContent.php
<?php
/**
* #file
* Contains \Drupal\docapi_migrate\Plugin\migrate\source\BookContent.
*/
namespace Drupal\example_migrate\Plugin\migrate\source;
use Drupal\migrate\Plugin\migrate\source\SqlBase;
use Drupal\migrate\Row;
/**
* Drupal 8 node from database.
*
* #MigrateSource(
* id = "book_content"
* )
*/
class BookContent extends SqlBase {
/**
* {#inheritdoc}
*/
public function query() {
$query = $this->select('docapi_migrate', 'dm')
->fields('dm', array('url', 'depth', 'body', 'meta'));
return $query;
}
/**
* {#inheritdoc}
*/
public function fields() {
$fields = array(
'url' => $this->t('Content url'),
'depth' => $this->t('Depth of the content'),
'body' => $this->t('Full text of the content'),
'meta' => $this->t('yaml data'),
);
return $fields;
}
However when I do:
drush migrate-import book_content
I get:
The drush command 'migrate-import book_content' could not be found.
I don't understand how this functions in BookContent.php work.
There should be the tags_field with is taxonomy reference, but I have no idea, where should I process the meta, so for example I get a list of Tags.
And when I have tags, how should I combine it, so the migration works.
I was searching via google for information, but nothing really make sense. How can I understand this?

Answer 1

You namespace is set to example_migrate. It needs to be set to the name of your module, so unless the module is called "example_migrate" it cannot find the class.
Change the name space to match YOUR_MODULE_NAME.
namespace Drupal\YOUR_MODULE_NAME\Plugin\migrate\source;
More about namespaces can be found when Googling for PSR0.