Sql.php

<?php

namespace Drupal\migrate\Plugin\migrate\id_map;

use Drupal\Core\Database\DatabaseException;
use Drupal\Core\Database\DatabaseExceptionWrapper;
use Drupal\Core\Field\BaseFieldDefinition;
use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
use Drupal\Core\Plugin\PluginBase;
use Drupal\migrate\MigrateMessage;
use Drupal\migrate\Audit\HighestIdInterface;
use Drupal\migrate\Plugin\MigrationInterface;
use Drupal\migrate\Event\MigrateIdMapMessageEvent;
use Drupal\migrate\MigrateException;
use Drupal\migrate\MigrateMessageInterface;
use Drupal\migrate\Plugin\MigrateIdMapInterface;
use Drupal\migrate\Row;
use Drupal\migrate\Event\MigrateEvents;
use Drupal\migrate\Event\MigrateMapSaveEvent;
use Drupal\migrate\Event\MigrateMapDeleteEvent;
use Symfony\Component\DependencyInjection\ContainerInterface;
use Symfony\Component\EventDispatcher\EventDispatcherInterface;

/**
 * Defines the sql based ID map implementation.
 *
 * It creates one map and one message table per migration entity to store the
 * relevant information.
 *
 * @PluginID("sql")
 */
class Sql extends PluginBase implements MigrateIdMapInterface, ContainerFactoryPluginInterface, HighestIdInterface {
    
    /**
     * Column name of hashed source id values.
     */
    const SOURCE_IDS_HASH = 'source_ids_hash';
    
    /**
     * An event dispatcher instance to use for map events.
     *
     * @var \Symfony\Component\EventDispatcher\EventDispatcherInterface
     */
    protected $eventDispatcher;
    
    /**
     * The migration map table name.
     *
     * @var string
     */
    protected $mapTableName;
    
    /**
     * The message table name.
     *
     * @var string
     */
    protected $messageTableName;
    
    /**
     * The migrate message service.
     *
     * @var \Drupal\migrate\MigrateMessageInterface
     */
    protected $message;
    
    /**
     * The database connection for the map/message tables on the destination.
     *
     * @var \Drupal\Core\Database\Connection
     */
    protected $database;
    
    /**
     * The select query.
     *
     * @var \Drupal\Core\Database\Query\SelectInterface
     */
    protected $query;
    
    /**
     * The migration being done.
     *
     * @var \Drupal\migrate\Plugin\MigrationInterface
     */
    protected $migration;
    
    /**
     * The source ID fields.
     *
     * @var array
     */
    protected $sourceIdFields;
    
    /**
     * The destination ID fields.
     *
     * @var array
     */
    protected $destinationIdFields;
    
    /**
     * Whether the plugin is already initialized.
     *
     * @var bool
     */
    protected $initialized;
    
    /**
     * The result.
     *
     * @var null
     */
    protected $result = NULL;
    
    /**
     * The source identifiers.
     *
     * @var array
     */
    protected $sourceIds = [];
    
    /**
     * The destination identifiers.
     *
     * @var array
     */
    protected $destinationIds = [];
    
    /**
     * The current row.
     *
     * @var null
     */
    protected $currentRow = NULL;
    
    /**
     * The current key.
     *
     * @var array
     */
    protected $currentKey = [];
    
    /**
     * Constructs an SQL object.
     *
     * Sets up the tables and builds the maps,
     *
     * @param array $configuration
     *   The configuration.
     * @param string $plugin_id
     *   The plugin ID for the migration process to do.
     * @param mixed $plugin_definition
     *   The configuration for the plugin.
     * @param \Drupal\migrate\Plugin\MigrationInterface $migration
     *   The migration to do.
     * @param \Symfony\Component\EventDispatcher\EventDispatcherInterface $event_dispatcher
     *   The event dispatcher.
     */
    public function __construct(array $configuration, $plugin_id, $plugin_definition, MigrationInterface $migration, EventDispatcherInterface $event_dispatcher) {
        parent::__construct($configuration, $plugin_id, $plugin_definition);
        $this->migration = $migration;
        $this->eventDispatcher = $event_dispatcher;
        $this->message = new MigrateMessage();
        if (!isset($this->database)) {
            $this->database = \Drupal::database();
        }
        // Default generated table names, limited to 63 characters.
        $machine_name = str_replace(':', '__', $this->migration
            ->id());
        $prefix_length = strlen($this->database
            ->tablePrefix());
        $this->mapTableName = 'migrate_map_' . mb_strtolower($machine_name);
        $this->mapTableName = mb_substr($this->mapTableName, 0, 63 - $prefix_length);
        $this->messageTableName = 'migrate_message_' . mb_strtolower($machine_name);
        $this->messageTableName = mb_substr($this->messageTableName, 0, 63 - $prefix_length);
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition, MigrationInterface $migration = NULL) {
        return new static($configuration, $plugin_id, $plugin_definition, $migration, $container->get('event_dispatcher'));
    }
    
    /**
     * Retrieves the hash of the source identifier values.
     *
     * @internal
     *
     * @param array $source_id_values
     *   The source identifiers
     *
     * @return string
     *   An hash containing the hashed values of the source identifiers.
     */
    public function getSourceIdsHash(array $source_id_values) {
        // When looking up the destination ID we require an array with both the
        // source key and value, e.g. ['nid' => 41]. In this case, $source_id_values
        // need to be ordered the same order as $this->sourceIdFields().
        // However, the Migration process plugin doesn't currently have a way to get
        // the source key so we presume the values have been passed through in the
        // correct order.
        if (!isset($source_id_values[0])) {
            $source_id_values_keyed = [];
            foreach ($this->sourceIdFields() as $field_name => $source_id) {
                $source_id_values_keyed[] = $source_id_values[$field_name];
            }
            $source_id_values = $source_id_values_keyed;
        }
        return hash('sha256', serialize(array_map('strval', $source_id_values)));
    }
    
    /**
     * The source ID fields.
     *
     * @return array
     *   The source ID fields.
     */
    protected function sourceIdFields() {
        if (!isset($this->sourceIdFields)) {
            // Build the source and destination identifier maps.
            $this->sourceIdFields = [];
            $count = 1;
            foreach ($this->migration
                ->getSourcePlugin()
                ->getIds() as $field => $schema) {
                $this->sourceIdFields[$field] = 'sourceid' . $count++;
            }
        }
        return $this->sourceIdFields;
    }
    
    /**
     * The destination ID fields.
     *
     * @return array
     *   The destination ID fields.
     */
    protected function destinationIdFields() {
        if (!isset($this->destinationIdFields)) {
            $this->destinationIdFields = [];
            $count = 1;
            foreach ($this->migration
                ->getDestinationPlugin()
                ->getIds() as $field => $schema) {
                $this->destinationIdFields[$field] = 'destid' . $count++;
            }
        }
        return $this->destinationIdFields;
    }
    
    /**
     * The name of the database map table.
     *
     * @return string
     *   The map table name.
     */
    public function mapTableName() {
        return $this->mapTableName;
    }
    
    /**
     * The name of the database message table.
     *
     * @return string
     *   The message table name.
     */
    public function messageTableName() {
        return $this->messageTableName;
    }
    
    /**
     * Get the fully qualified map table name.
     *
     * @return string
     *   The fully qualified map table name.
     */
    public function getQualifiedMapTableName() {
        return $this->getDatabase()
            ->getFullQualifiedTableName($this->mapTableName);
    }
    
    /**
     * Gets the database connection.
     *
     * @return \Drupal\Core\Database\Connection
     *   The database connection object.
     */
    public function getDatabase() {
        $this->init();
        return $this->database;
    }
    
    /**
     * Initialize the plugin.
     */
    protected function init() {
        if (!$this->initialized) {
            $this->initialized = TRUE;
            $this->ensureTables();
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function setMessage(MigrateMessageInterface $message) {
        $this->message = $message;
    }
    
    /**
     * Create the map and message tables if they don't already exist.
     */
    protected function ensureTables() {
        if (!$this->getDatabase()
            ->schema()
            ->tableExists($this->mapTableName)) {
            // Generate appropriate schema info for the map and message tables,
            // and map from the source field names to the map/msg field names.
            $count = 1;
            $source_id_schema = [];
            $indexes = [];
            foreach ($this->migration
                ->getSourcePlugin()
                ->getIds() as $id_definition) {
                $mapkey = 'sourceid' . $count++;
                $indexes['source'][] = $mapkey;
                $source_id_schema[$mapkey] = $this->getFieldSchema($id_definition);
                $source_id_schema[$mapkey]['not null'] = TRUE;
            }
            $source_ids_hash[$this::SOURCE_IDS_HASH] = [
                'type' => 'varchar',
                'length' => '64',
                'not null' => TRUE,
                'description' => 'Hash of source ids. Used as primary key',
            ];
            $fields = $source_ids_hash + $source_id_schema;
            // Add destination identifiers to map table.
            // @todo How do we discover the destination schema?
            $count = 1;
            foreach ($this->migration
                ->getDestinationPlugin()
                ->getIds() as $id_definition) {
                // Allow dest identifier fields to be NULL (for IGNORED/FAILED cases).
                $mapkey = 'destid' . $count++;
                $fields[$mapkey] = $this->getFieldSchema($id_definition);
                $fields[$mapkey]['not null'] = FALSE;
            }
            $fields['source_row_status'] = [
                'type' => 'int',
                'size' => 'tiny',
                'unsigned' => TRUE,
                'not null' => TRUE,
                'default' => MigrateIdMapInterface::STATUS_IMPORTED,
                'description' => 'Indicates current status of the source row',
            ];
            $fields['rollback_action'] = [
                'type' => 'int',
                'size' => 'tiny',
                'unsigned' => TRUE,
                'not null' => TRUE,
                'default' => MigrateIdMapInterface::ROLLBACK_DELETE,
                'description' => 'Flag indicating what to do for this item on rollback',
            ];
            $fields['last_imported'] = [
                'type' => 'int',
                'unsigned' => TRUE,
                'not null' => TRUE,
                'default' => 0,
                'description' => 'UNIX timestamp of the last time this row was imported',
            ];
            $fields['hash'] = [
                'type' => 'varchar',
                'length' => '64',
                'not null' => FALSE,
                'description' => 'Hash of source row data, for detecting changes',
            ];
            $schema = [
                'description' => 'Mappings from source identifier value(s) to destination identifier value(s).',
                'fields' => $fields,
                'primary key' => [
                    $this::SOURCE_IDS_HASH,
                ],
                'indexes' => $indexes,
            ];
            $this->getDatabase()
                ->schema()
                ->createTable($this->mapTableName, $schema);
            // Now do the message table.
            if (!$this->getDatabase()
                ->schema()
                ->tableExists($this->messageTableName())) {
                $fields = [];
                $fields['msgid'] = [
                    'type' => 'serial',
                    'unsigned' => TRUE,
                    'not null' => TRUE,
                ];
                $fields += $source_ids_hash;
                $fields['level'] = [
                    'type' => 'int',
                    'unsigned' => TRUE,
                    'not null' => TRUE,
                    'default' => 1,
                ];
                $fields['message'] = [
                    'type' => 'text',
                    'size' => 'medium',
                    'not null' => TRUE,
                ];
                $schema = [
                    'description' => 'Messages generated during a migration process',
                    'fields' => $fields,
                    'primary key' => [
                        'msgid',
                    ],
                ];
                $this->getDatabase()
                    ->schema()
                    ->createTable($this->messageTableName(), $schema);
            }
        }
        else {
            // Add any missing columns to the map table.
            if (!$this->getDatabase()
                ->schema()
                ->fieldExists($this->mapTableName, 'rollback_action')) {
                $this->getDatabase()
                    ->schema()
                    ->addField($this->mapTableName, 'rollback_action', [
                    'type' => 'int',
                    'size' => 'tiny',
                    'unsigned' => TRUE,
                    'not null' => TRUE,
                    'default' => 0,
                    'description' => 'Flag indicating what to do for this item on rollback',
                ]);
            }
            if (!$this->getDatabase()
                ->schema()
                ->fieldExists($this->mapTableName, 'hash')) {
                $this->getDatabase()
                    ->schema()
                    ->addField($this->mapTableName, 'hash', [
                    'type' => 'varchar',
                    'length' => '64',
                    'not null' => FALSE,
                    'description' => 'Hash of source row data, for detecting changes',
                ]);
            }
            if (!$this->getDatabase()
                ->schema()
                ->fieldExists($this->mapTableName, $this::SOURCE_IDS_HASH)) {
                $this->getDatabase()
                    ->schema()
                    ->addField($this->mapTableName, $this::SOURCE_IDS_HASH, [
                    'type' => 'varchar',
                    'length' => '64',
                    'not null' => TRUE,
                    'description' => 'Hash of source ids. Used as primary key',
                ]);
            }
        }
    }
    
    /**
     * Creates schema from an ID definition.
     *
     * @param array $id_definition
     *   The definition of the field having the structure as the items returned by
     *   MigrateSourceInterface or MigrateDestinationInterface::getIds().
     *
     * @return array
     *   The database schema definition.
     *
     * @see \Drupal\migrate\Plugin\MigrateSourceInterface::getIds()
     * @see \Drupal\migrate\Plugin\MigrateDestinationInterface::getIds()
     */
    protected function getFieldSchema(array $id_definition) {
        $type_parts = explode('.', $id_definition['type']);
        if (count($type_parts) == 1) {
            $type_parts[] = 'value';
        }
        unset($id_definition['type']);
        // Get the field storage definition.
        $definition = BaseFieldDefinition::create($type_parts[0]);
        // Get a list of setting keys belonging strictly to the field definition.
        $default_field_settings = $definition->getSettings();
        // Separate field definition settings from custom settings. Custom settings
        // are settings passed in $id_definition that are not part of field storage
        // definition settings.
        $field_settings = array_intersect_key($id_definition, $default_field_settings);
        $custom_settings = array_diff_key($id_definition, $default_field_settings);
        // Resolve schema from field storage definition settings.
        $schema = $definition->setSettings($field_settings)
            ->getColumns()[$type_parts[1]];
        // Merge back custom settings.
        return $schema + $custom_settings;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getRowBySource(array $source_id_values) {
        $query = $this->getDatabase()
            ->select($this->mapTableName(), 'map')
            ->fields('map');
        $query->condition($this::SOURCE_IDS_HASH, $this->getSourceIdsHash($source_id_values));
        $result = $query->execute();
        return $result->fetchAssoc();
    }
    
    /**
     * {@inheritdoc}
     */
    public function getRowByDestination(array $destination_id_values) {
        $query = $this->getDatabase()
            ->select($this->mapTableName(), 'map')
            ->fields('map');
        foreach ($this->destinationIdFields() as $field_name => $destination_id) {
            $query->condition("map.{$destination_id}", $destination_id_values[$field_name], '=');
        }
        $result = $query->execute();
        return $result->fetchAssoc();
    }
    
    /**
     * {@inheritdoc}
     */
    public function getRowsNeedingUpdate($count) {
        $rows = [];
        $result = $this->getDatabase()
            ->select($this->mapTableName(), 'map')
            ->fields('map')
            ->condition('source_row_status', MigrateIdMapInterface::STATUS_NEEDS_UPDATE)
            ->range(0, $count)
            ->execute();
        foreach ($result as $row) {
            $rows[] = $row;
        }
        return $rows;
    }
    
    /**
     * {@inheritdoc}
     */
    public function lookupSourceId(array $destination_id_values) {
        $source_id_fields = $this->sourceIdFields();
        $query = $this->getDatabase()
            ->select($this->mapTableName(), 'map');
        foreach ($source_id_fields as $source_field_name => $idmap_field_name) {
            $query->addField('map', $idmap_field_name, $source_field_name);
        }
        foreach ($this->destinationIdFields() as $field_name => $destination_id) {
            $query->condition("map.{$destination_id}", $destination_id_values[$field_name], '=');
        }
        $result = $query->execute();
        return $result->fetchAssoc() ?: [];
    }
    
    /**
     * {@inheritdoc}
     */
    public function lookupDestinationId(array $source_id_values) {
        @trigger_error(__NAMESPACE__ . '\\Sql::lookupDestinationId() is deprecated in drupal:8.1.0 and is removed from drupal:9.0.0. Use Sql::lookupDestinationIds() instead. See https://www.drupal.org/node/2725809', E_USER_DEPRECATED);
        $results = $this->lookupDestinationIds($source_id_values);
        return $results ? reset($results) : [];
    }
    
    /**
     * {@inheritdoc}
     */
    public function lookupDestinationIds(array $source_id_values) {
        if (empty($source_id_values)) {
            return [];
        }
        // Canonicalize the keys into a hash of DB-field => value.
        $is_associative = !isset($source_id_values[0]);
        $conditions = [];
        foreach ($this->sourceIdFields() as $field_name => $db_field) {
            if ($is_associative) {
                // Ensure to handle array elements with a NULL value.
                if (array_key_exists($field_name, $source_id_values)) {
                    // Associative $source_id_values can have fields out of order.
                    if (isset($source_id_values[$field_name])) {
                        // Only add a condition if the value is not NULL.
                        $conditions[$db_field] = $source_id_values[$field_name];
                    }
                    unset($source_id_values[$field_name]);
                }
            }
            else {
                // For non-associative $source_id_values, we assume they're the first
                // few fields.
                if (empty($source_id_values)) {
                    break;
                }
                $conditions[$db_field] = array_shift($source_id_values);
            }
        }
        if (!empty($source_id_values)) {
            $var_dump = var_export($source_id_values, TRUE);
            throw new MigrateException(sprintf("Extra unknown items for map %s in source IDs: %s", $this->mapTableName(), $var_dump));
        }
        $query = $this->getDatabase()
            ->select($this->mapTableName(), 'map')
            ->fields('map', $this->destinationIdFields());
        if (count($this->sourceIdFields()) === count($conditions)) {
            // Optimization: Use the primary key.
            $query->condition($this::SOURCE_IDS_HASH, $this->getSourceIdsHash(array_values($conditions)));
        }
        else {
            foreach ($conditions as $db_field => $value) {
                $query->condition($db_field, $value);
            }
        }
        try {
            return $query->execute()
                ->fetchAll(\PDO::FETCH_NUM);
        } catch (DatabaseExceptionWrapper $e) {
            // It's possible that the query will cause an exception to be thrown. For
            // example, the URL alias migration uses a dummy node ID of 'INVALID_NID'
            // to cause the lookup to return no results. On PostgreSQL this causes an
            // exception because 'INVALID_NID' is not the expected type.
            return [];
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function saveIdMapping(Row $row, array $destination_id_values, $source_row_status = MigrateIdMapInterface::STATUS_IMPORTED, $rollback_action = MigrateIdMapInterface::ROLLBACK_DELETE) {
        // Construct the source key.
        $source_id_values = $row->getSourceIdValues();
        // Construct the source key and initialize to empty variable keys.
        $fields = [];
        foreach ($this->sourceIdFields() as $field_name => $key_name) {
            // A NULL key value is usually an indication of a problem.
            if (!isset($source_id_values[$field_name])) {
                $this->message
                    ->display($this->t('Did not save to map table due to NULL value for key field @field', [
                    '@field' => $field_name,
                ]), 'error');
                return;
            }
            $fields[$key_name] = $source_id_values[$field_name];
        }
        if (!$fields) {
            return;
        }
        $fields += [
            'source_row_status' => (int) $source_row_status,
            'rollback_action' => (int) $rollback_action,
            'hash' => $row->getHash(),
        ];
        $count = 0;
        foreach ($destination_id_values as $dest_id) {
            $fields['destid' . ++$count] = $dest_id;
        }
        if ($count && $count != count($this->destinationIdFields())) {
            $this->message
                ->display(t('Could not save to map table due to missing destination id values'), 'error');
            return;
        }
        if ($this->migration
            ->getTrackLastImported()) {
            $fields['last_imported'] = time();
        }
        $keys = [
            $this::SOURCE_IDS_HASH => $this->getSourceIdsHash($source_id_values),
        ];
        // Notify anyone listening of the map row we're about to save.
        $this->eventDispatcher
            ->dispatch(MigrateEvents::MAP_SAVE, new MigrateMapSaveEvent($this, $fields));
        $this->getDatabase()
            ->merge($this->mapTableName())
            ->key($keys)
            ->fields($fields)
            ->execute();
    }
    
    /**
     * {@inheritdoc}
     */
    public function saveMessage(array $source_id_values, $message, $level = MigrationInterface::MESSAGE_ERROR) {
        foreach ($this->sourceIdFields() as $field_name => $source_id) {
            // If any key value is not set, we can't save.
            if (!isset($source_id_values[$field_name])) {
                return;
            }
        }
        $fields[$this::SOURCE_IDS_HASH] = $this->getSourceIdsHash($source_id_values);
        $fields['level'] = $level;
        $fields['message'] = $message;
        $this->getDatabase()
            ->insert($this->messageTableName())
            ->fields($fields)
            ->execute();
        // Notify anyone listening of the message we've saved.
        $this->eventDispatcher
            ->dispatch(MigrateEvents::IDMAP_MESSAGE, new MigrateIdMapMessageEvent($this->migration, $source_id_values, $message, $level));
    }
    
    /**
     * {@inheritdoc}
     */
    public function getMessages(array $source_id_values = [], $level = NULL) {
        $query = $this->getDatabase()
            ->select($this->messageTableName(), 'msg');
        $condition = sprintf('msg.%s = map.%s', $this::SOURCE_IDS_HASH, $this::SOURCE_IDS_HASH);
        $query->addJoin('LEFT', $this->mapTableName(), 'map', $condition);
        // Explicitly define the fields we want. The order will be preserved: source
        // IDs, destination IDs (if possible), and then the rest.
        foreach ($this->sourceIdFields() as $id => $column_name) {
            $query->addField('map', $column_name, "src_{$id}");
        }
        foreach ($this->destinationIdFields() as $id => $column_name) {
            $query->addField('map', $column_name, "dest_{$id}");
        }
        $query->fields('msg', [
            'msgid',
            $this::SOURCE_IDS_HASH,
            'level',
            'message',
        ]);
        if ($source_id_values) {
            $query->condition('msg.' . $this::SOURCE_IDS_HASH, $this->getSourceIdsHash($source_id_values));
        }
        if ($level) {
            $query->condition('msg.level', $level);
        }
        return $query->execute();
    }
    
    /**
     * {@inheritdoc}
     */
    public function getMessageIterator(array $source_id_values = [], $level = NULL) {
        @trigger_error('getMessageIterator() is deprecated in drupal:8.8.0 and is removed from drupal:9.0.0. Use getMessages() instead. See https://www.drupal.org/node/3060969', E_USER_DEPRECATED);
        return $this->getMessages($source_id_values, $level);
    }
    
    /**
     * {@inheritdoc}
     */
    public function prepareUpdate() {
        $this->getDatabase()
            ->update($this->mapTableName())
            ->fields([
            'source_row_status' => MigrateIdMapInterface::STATUS_NEEDS_UPDATE,
        ])
            ->execute();
    }
    
    /**
     * {@inheritdoc}
     */
    public function processedCount() {
        return $this->countHelper(NULL, $this->mapTableName());
    }
    
    /**
     * {@inheritdoc}
     */
    public function importedCount() {
        return $this->countHelper([
            MigrateIdMapInterface::STATUS_IMPORTED,
            MigrateIdMapInterface::STATUS_NEEDS_UPDATE,
        ]);
    }
    
    /**
     * {@inheritdoc}
     */
    public function updateCount() {
        return $this->countHelper(MigrateIdMapInterface::STATUS_NEEDS_UPDATE);
    }
    
    /**
     * {@inheritdoc}
     */
    public function errorCount() {
        return $this->countHelper(MigrateIdMapInterface::STATUS_FAILED);
    }
    
    /**
     * {@inheritdoc}
     */
    public function messageCount() {
        return $this->countHelper(NULL, $this->messageTableName());
    }
    
    /**
     * Counts records in a table.
     *
     * @param int|array $status
     *   (optional) Status code(s) to filter the source_row_status column.
     * @param string $table
     *   (optional) The table to work. Defaults to NULL.
     *
     * @return int
     *   The number of records.
     */
    protected function countHelper($status = NULL, $table = NULL) {
        // Use database directly to avoid creating tables.
        $query = $this->database
            ->select($table ?: $this->mapTableName());
        if (isset($status)) {
            $query->condition('source_row_status', $status, is_array($status) ? 'IN' : '=');
        }
        try {
            $count = (int) $query->countQuery()
                ->execute()
                ->fetchField();
        } catch (DatabaseException $e) {
            // The table does not exist, therefore there are no records.
            $count = 0;
        }
        return $count;
    }
    
    /**
     * {@inheritdoc}
     */
    public function delete(array $source_id_values, $messages_only = FALSE) {
        if (empty($source_id_values)) {
            throw new MigrateException('Without source identifier values it is impossible to find the row to delete.');
        }
        if (!$messages_only) {
            $map_query = $this->getDatabase()
                ->delete($this->mapTableName());
            $map_query->condition($this::SOURCE_IDS_HASH, $this->getSourceIdsHash($source_id_values));
            // Notify anyone listening of the map row we're about to delete.
            $this->eventDispatcher
                ->dispatch(MigrateEvents::MAP_DELETE, new MigrateMapDeleteEvent($this, $source_id_values));
            $map_query->execute();
        }
        $message_query = $this->getDatabase()
            ->delete($this->messageTableName());
        $message_query->condition($this::SOURCE_IDS_HASH, $this->getSourceIdsHash($source_id_values));
        $message_query->execute();
    }
    
    /**
     * {@inheritdoc}
     */
    public function deleteDestination(array $destination_id_values) {
        $map_query = $this->getDatabase()
            ->delete($this->mapTableName());
        $message_query = $this->getDatabase()
            ->delete($this->messageTableName());
        $source_id_values = $this->lookupSourceId($destination_id_values);
        if (!empty($source_id_values)) {
            foreach ($this->destinationIdFields() as $field_name => $destination_id) {
                $map_query->condition($destination_id, $destination_id_values[$field_name]);
            }
            // Notify anyone listening of the map row we're about to delete.
            $this->eventDispatcher
                ->dispatch(MigrateEvents::MAP_DELETE, new MigrateMapDeleteEvent($this, $source_id_values));
            $map_query->execute();
            $message_query->condition($this::SOURCE_IDS_HASH, $this->getSourceIdsHash($source_id_values));
            $message_query->execute();
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function setUpdate(array $source_id_values) {
        if (empty($source_id_values)) {
            throw new MigrateException('No source identifiers provided to update.');
        }
        $query = $this->getDatabase()
            ->update($this->mapTableName())
            ->fields([
            'source_row_status' => MigrateIdMapInterface::STATUS_NEEDS_UPDATE,
        ]);
        foreach ($this->sourceIdFields() as $field_name => $source_id) {
            $query->condition($source_id, $source_id_values[$field_name]);
        }
        $query->execute();
    }
    
    /**
     * {@inheritdoc}
     */
    public function clearMessages() {
        $this->getDatabase()
            ->truncate($this->messageTableName())
            ->execute();
    }
    
    /**
     * {@inheritdoc}
     */
    public function destroy() {
        $this->getDatabase()
            ->schema()
            ->dropTable($this->mapTableName());
        $this->getDatabase()
            ->schema()
            ->dropTable($this->messageTableName());
    }
    
    /**
     * Implementation of \Iterator::rewind().
     *
     * This is called before beginning a foreach loop.
     */
    public function rewind() {
        $this->currentRow = NULL;
        $fields = [];
        foreach ($this->sourceIdFields() as $field) {
            $fields[] = $field;
        }
        foreach ($this->destinationIdFields() as $field) {
            $fields[] = $field;
        }
        $this->result = $this->getDatabase()
            ->select($this->mapTableName(), 'map')
            ->fields('map', $fields)
            ->orderBy('destid1')
            ->execute();
        $this->next();
    }
    
    /**
     * Implementation of \Iterator::current().
     *
     * This is called when entering a loop iteration, returning the current row.
     */
    public function current() {
        return $this->currentRow;
    }
    
    /**
     * Implementation of \Iterator::key().
     *
     * This is called when entering a loop iteration, returning the key of the
     * current row. It must be a scalar - we will serialize to fulfill the
     * requirement, but using getCurrentKey() is preferable.
     */
    public function key() {
        return serialize($this->currentKey);
    }
    
    /**
     * {@inheritdoc}
     */
    public function currentDestination() {
        if ($this->valid()) {
            $result = [];
            foreach ($this->destinationIdFields() as $destination_field_name => $idmap_field_name) {
                if (!is_null($this->currentRow[$idmap_field_name])) {
                    $result[$destination_field_name] = $this->currentRow[$idmap_field_name];
                }
            }
            return $result;
        }
        else {
            return NULL;
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function currentSource() {
        if ($this->valid()) {
            $result = [];
            foreach ($this->sourceIdFields() as $field_name => $source_id) {
                $result[$field_name] = $this->currentKey[$source_id];
            }
            return $result;
        }
        else {
            return NULL;
        }
    }
    
    /**
     * Implementation of \Iterator::next().
     *
     * This is called at the bottom of the loop implicitly, as well as explicitly
     * from rewind().
     */
    public function next() {
        $this->currentRow = $this->result
            ->fetchAssoc();
        $this->currentKey = [];
        if ($this->currentRow) {
            foreach ($this->sourceIdFields() as $map_field) {
                $this->currentKey[$map_field] = $this->currentRow[$map_field];
                // Leave only destination fields.
                unset($this->currentRow[$map_field]);
            }
        }
    }
    
    /**
     * Implementation of \Iterator::valid().
     *
     * This is called at the top of the loop, returning TRUE to process the loop
     * and FALSE to terminate it.
     */
    public function valid() {
        return $this->currentRow !== FALSE;
    }
    
    /**
     * Returns the migration plugin manager.
     *
     * @todo Inject as a dependency in https://www.drupal.org/node/2919158.
     *
     * @return \Drupal\migrate\Plugin\MigrationPluginManagerInterface
     *   The migration plugin manager.
     */
    protected function getMigrationPluginManager() {
        return \Drupal::service('plugin.manager.migration');
    }
    
    /**
     * {@inheritdoc}
     */
    public function getHighestId() {
        // Ensure that the first ID is an integer.
        $keys = $this->migration
            ->getDestinationPlugin()
            ->getIds();
        if (reset($keys)['type'] !== 'integer') {
            throw new \LogicException('To determine the highest migrated ID the first ID must be an integer');
        }
        // List of mapping tables to look in for the highest ID.
        $map_tables = [
            $this->migration
                ->id() => $this->mapTableName(),
        ];
        // If there's a bundle, it means we have a derived migration and we need to
        // find all the mapping tables from the related derived migrations.
        if ($base_id = substr($this->migration
            ->id(), 0, strpos($this->migration
            ->id(), $this::DERIVATIVE_SEPARATOR))) {
            $migration_manager = $this->getMigrationPluginManager();
            $migrations = $migration_manager->getDefinitions();
            foreach ($migrations as $migration_id => $migration) {
                if ($migration['id'] === $base_id) {
                    // Get this derived migration's mapping table and add it to the list
                    // of mapping tables to look in for the highest ID.
                    $stub = $migration_manager->createInstance($migration_id);
                    $map_tables[$migration_id] = $stub->getIdMap()
                        ->mapTableName();
                }
            }
        }
        // Get the highest id from the list of map tables.
        $ids = [
            0,
        ];
        foreach ($map_tables as $map_table) {
            // If the map_table does not exist then continue on to the next map_table.
            if (!$this->getDatabase()
                ->schema()
                ->tableExists($map_table)) {
                continue;
            }
            $query = $this->getDatabase()
                ->select($map_table, 'map')
                ->fields('map', $this->destinationIdFields())
                ->range(0, 1);
            foreach (array_values($this->destinationIdFields()) as $order_field) {
                $query->orderBy($order_field, 'DESC');
            }
            $ids[] = $query->execute()
                ->fetchField();
        }
        // Return the highest of all the mapped IDs.
        return (int) max($ids);
    }

}