feat: logic func which will throw exception if core WP tables are empty.

src/Command/General/ContentDiffMigrator.php

@@ -8,8 +8,10 @@
 namespace NewspackCustomContentMigrator\Command\General;
 
 use NewspackCustomContentMigrator\Command\InterfaceCommand;
+use NewspackCustomContentMigrator\Exceptions\CoreWPTableEmptyException;
 use NewspackCustomContentMigrator\Logic\ContentDiffMigrator as ContentDiffMigratorLogic;
 use NewspackCustomContentMigrator\Utils\PHP as PHPUtil;
+use RuntimeException;
 use WP_CLI;
 
 /**
@@ -385,7 +387,7 @@ public function cmd_search_new_content_on_live( $args, $assoc_args ) {
 		global $wpdb;
 		try {
 			$this->validate_db_tables( $live_table_prefix, [ 'options' ] );
-		} catch ( \RuntimeException $e ) {
+		} catch ( RuntimeException $e ) {
 			WP_CLI::warning( $e->getMessage() );
 			WP_CLI::line( "Now running command `newspack-content-migrator correct-collations-for-live-wp-tables --live-table-prefix={$live_table_prefix} --mode=generous --skip-tables=options` ..." );
 			$this->cmd_correct_collations_for_live_wp_tables(
@@ -396,6 +398,16 @@ public function cmd_search_new_content_on_live( $args, $assoc_args ) {
 					'skip-tables'       => 'options',
 				]
 			);
+		} catch ( CoreWPTableEmptyException $e ) {
+			// If one of the empty tables is wp_links, we can ignore it. Add any other tables we can ignore to the array below.
+			$ignore_empty_tables = [
+				$live_table_prefix . 'links',
+				$live_table_prefix . 'termmeta',
+				$live_table_prefix . 'comments',
+				$live_table_prefix . 'commentmeta',
+			];
+
+			$this->handle_core_wp_table_empty_exception( $e, $ignore_empty_tables );
 		}
 
 		// Search distinct Post types in live DB.
@@ -500,7 +512,7 @@ public function cmd_migrate_live_content( $args, $assoc_args ) {
 		// Validate DBs.
 		try {
 			$this->validate_db_tables( $live_table_prefix, [ 'options' ] );
-		} catch ( \RuntimeException $e ) {
+		} catch ( RuntimeException $e ) {
 			WP_CLI::warning( $e->getMessage() );
 			WP_CLI::line( "Now running command `newspack-content-migrator correct-collations-for-live-wp-tables --live-table-prefix={$live_table_prefix} --mode=generous --skip-tables=options` ..." );
 			$this->cmd_correct_collations_for_live_wp_tables(
@@ -511,6 +523,16 @@ public function cmd_migrate_live_content( $args, $assoc_args ) {
 					'skip-tables'       => 'options',
 				]
 			);
+		} catch ( CoreWPTableEmptyException $e ) {
+			// If one of the empty tables is wp_links, we can ignore it. Add any other tables we can ignore to the array below.
+			$ignore_empty_tables = [
+				$live_table_prefix . 'links',
+				$live_table_prefix . 'termmeta',
+				$live_table_prefix . 'comments',
+				$live_table_prefix . 'commentmeta',
+			];
+
+			$this->handle_core_wp_table_empty_exception( $e, $ignore_empty_tables );
 		}
 
 		// Set constants.
@@ -1157,7 +1179,7 @@ public function cmd_correct_collations_for_live_wp_tables( $args, $assoc_args )
 	 * @param string $where_operand           Search operand, can be '==' or '!='.
 	 * @param bool   $return_first            If true, return just the first matched entry, otherwise returns all matched entries.
 	 *
-	 * @throws \RuntimeException In case an unsupported $where_operand was given.
+	 * @throws RuntimeException In case an unsupported $where_operand was given.
 	 *
 	 * @return array Found results. Mind that if $return_first is true, it will return a one-dimensional array,
 	 *               and if $return_first is false, it will return two-dimensional array with all matched elements as subarrays.
@@ -1168,7 +1190,7 @@ private function filter_imported_posts_log( array $imported_posts_log_data, stri
 
 		// Validate $where_operand.
 		if ( ! in_array( $where_operand, $supported_where_operands ) ) {
-			throw new \RuntimeException( sprintf( 'Where operand %s is not supported.', $where_operand ) );
+			throw new RuntimeException( sprintf( 'Where operand %s is not supported.', $where_operand ) );
 		}
 
 		foreach ( $imported_posts_log_data as $entry ) {
@@ -1286,21 +1308,41 @@ private function get_data_from_log( $log, $json_keys ) {
 		return $data;
 	}
 
+	/**
+	 * Handles CoreWPTableEmptyException.
+	 *
+	 * @param CoreWPTableEmptyException $e Exception object which specifies which tables are empty.
+	 * @param array                     $ignore_empty_tables Array of tables to ignore if empty.
+	 *
+	 * @return void
+	 */
+	private function handle_core_wp_table_empty_exception( CoreWPTableEmptyException $e, array $ignore_empty_tables ) {
+		$empty_tables = array_diff( $e->get_tables(), $ignore_empty_tables );
+		if ( empty( $empty_tables ) ) {
+			WP_CLI::warning( sprintf( 'One, or all, of the following tables may be empty and will be ignored: %s', implode( $ignore_empty_tables ) ) );
+		} else {
+			WP_CLI::error( sprintf( 'In order for the content diff operation to proceed, the following empty tables must be addressed: %s', implode( $empty_tables ) ) );
+		}
+	}
+
 	/**
 	 * Validates DB tables.
 	 *
 	 * @param string $live_table_prefix Live table prefix.
 	 * @param array  $skip_tables       Core WP DB tables to skip (without prefix).
 	 *
-	 * @throws \RuntimeException In case that table collations do not match.
-	 *
 	 * @return void
+	 * @throws RuntimeException In case that table collations do not match.
+	 * @throws CoreWPTableEmptyException In case that some of the core WP tables are empty.
 	 */
 	public function validate_db_tables( string $live_table_prefix, array $skip_tables ): void {
 		self::$logic->validate_core_wp_db_tables_exist_in_db( $live_table_prefix, $skip_tables );
+
 		if ( ! self::$logic->are_table_collations_matching( $live_table_prefix, $skip_tables ) ) {
-			throw new \RuntimeException( 'Table collations do not match for some (or all) WP tables.' );
+			throw new RuntimeException( 'Table collations do not match for some (or all) WP tables.' );
 		}
+
+		self::$logic->validate_core_wp_db_tables_are_not_empty( $live_table_prefix, $skip_tables );
 	}
 
 	/**

src/Exceptions/CoreWPTableEmptyException.php

@@ -0,0 +1,44 @@
+<?php
+/**
+ * CoreWPTableEmptyException class.
+ *
+ * @package NewspackCustomContentMigrator\Exceptions
+ */
+
+namespace NewspackCustomContentMigrator\Exceptions;
+
+/**
+ * Class CoreWPTableEmptyException.
+ *
+ * This class facilitates the handling of instances where core WP tables are empty. It might be necessary
+ * to ignore certain tables even if they are empty. This class will allow us to obtain that list of
+ * empty core tables and allow us to make a decision on a case-by-case basis how to proceed.
+ */
+class CoreWPTableEmptyException extends \Exception {
+
+	/**
+	 * Array of table names that are empty.
+	 *
+	 * @var string[] $tables Names of empty tables.
+	 */
+	protected array $tables = [];
+
+	/**
+	 * Constructor.
+	 *
+	 * @param string[] $tables Table names.
+	 */
+	public function __construct( array $tables ) {
+		$this->tables = $tables;
+		parent::__construct( sprintf( 'The following core WP Tables are empty: %s', implode( $this->tables ) ) );
+	}
+
+	/**
+	 * Returns the names of the empty tables.
+	 *
+	 * @return string[]
+	 */
+	public function get_tables(): array {
+		return $this->tables;
+	}
+}

src/Logic/ContentDiffMigrator.php

@@ -7,6 +7,7 @@
 
 namespace NewspackCustomContentMigrator\Logic;
 
+use NewspackCustomContentMigrator\Exceptions\CoreWPTableEmptyException;
 use \WP_CLI;
 use \WP_User;
 use NewspackContentConverter\ContentPatcher\ElementManipulators\WpBlockManipulator;
@@ -3181,6 +3182,39 @@ public function copy_table_data_using_proper_collation( string $prefix, string $
 		}
 	}
 
+	/**
+	 * This function will ensure that the core WP DB tables are not empty. This is especially important
+	 * for tables like wp_terms, wp_term_taxonomy, and wp_term_relationships. If these tables are empty,
+	 * the site's taxonomies will not be recreated, and no terms will be associated with posts.
+	 *
+	 * @param string $table_prefix Table prefix.
+	 * @param string[] $skip_tables Core WP DB tables to skip (without prefix).
+	 *
+	 * @return void
+	 * @throws CoreWPTableEmptyException
+	 */
+    public function validate_core_wp_db_tables_are_not_empty( string $table_prefix, array $skip_tables = [] )
+    {
+        $empty_tables = [];
+
+        foreach ( self::CORE_WP_TABLES as $core_table ) {
+            if ( in_array( $core_table, $skip_tables ) ) {
+                continue;
+            }
+
+            $table_name = $table_prefix . $core_table;
+            $count = intval( $this->wpdb->get_var( "SELECT COUNT(*) FROM $table_name" ) );
+
+            if ( 0 === $count ) {
+                $empty_tables[] = $table_name;
+            }
+        }
+
+        if ( ! empty( $empty_tables ) ) {
+            throw new CoreWPTableEmptyException( $empty_tables );
+        }
+    }
+
 	/**
 	 * Wrapper for WP's native \get_user_by(), for easier testing.
 	 *