NEW Allow setting sql_mode via config (#9721)

docs/en/00_Getting_Started/00_Server_Requirements.md

@@ -28,6 +28,10 @@ Use [phpinfo()](http://php.net/manual/en/function.phpinfo.php) to inspect your c
  * SQL Server ([third party module](https://addons.silverstripe.org/add-ons/silverstripe/mssql), community supported)
  * SQLite ([third party module](https://addons.silverstripe.org/add-ons/silverstripe/sqlite3), community supported)
 
+ ### Connection mode (sql_mode) when using MySQL server >=5.7.5
+
+In MySQL versions >=5.7.5, the `ANSI` sql_mode setting behaves differently and includes the `ONLY_FULL_GROUP_BY` setting. It is generally recommended to leave this setting as-is because it results in deterministic SQL. However, for some advanced cases, the sql_mode can be configured on the database connection via the configuration API (see `MySQLDatabase::$sql_mode` for more details.) This setting is only available in Silverstripe CMS 4.7 and later.
+
 ## Webserver Configuration
 
 ### Overview

docs/en/04_Changelogs/4.7.0.md

@@ -5,6 +5,7 @@
 - [Experimental support for PHP 8](#experimental-support-for-php-8)
 - [Support for Symfony 4 Components](#support-for-symfony-4-components)
 - [Default MySQL collation updated](#default-mysql-collation-updated)
+- [MySQL connection mode configurable](#mysql-connection-mode-now-configurable)
 - [Flysystem dependency shifted](#flysystem-dependency-shifted)
 
 ## New features
@@ -59,6 +60,10 @@ You can rectify this by upgrading MySQL, enabling the `innodb_large_prefix` sett
 reducing the size of affected fields. If none of these solutions are currently suitable, you can
 remove the new collation configuration to default back to the previous default collation.
 
+### MySQL connection mode now configurable
+
+In MySQL versions >=5.7.5, the `ANSI` sql_mode setting behaves differently and includes the `ONLY_FULL_GROUP_BY` setting. It is generally recommended to leave this setting as-is because it results in deterministic SQL. However, for some advanced cases, the sql_mode can now be configured on the database connection via the configuration API (see `MySQLDatabase::$sql_mode` for more details.)
+
 ### Flysystem dependency shifted
 
 Previously the Flysystem package was pulled in via the `silverstripe/framework` module, but only
@@ -71,4 +76,3 @@ An edgecase exists where a project can update to `silverstripe/framework 4.7.0`
 `silverstripe/assets 1.6.x`, and lose the Flysystem dependency entirely. The best way to avoid this
 is by ensuring you update all core modules to the new minor release at once, ideally through a core
 recipe like `silverstripe/recipe-core`.
-

src/ORM/Connect/MySQLDatabase.php

@@ -49,6 +49,15 @@ class MySQLDatabase extends Database implements TransactionManager
      */
     private static $charset = 'utf8';
 
+    /**
+     * SQL Mode used on connections to MySQL. Defaults to ANSI. For basic ORM
+     * compatibility, this setting must always include ANSI or ANSI_QUOTES.
+     *
+     * @config
+     * @var string
+     */
+    private static $sql_mode = 'ANSI';
+
     /**
      * Cache for getTransactionManager()
      *
@@ -84,8 +93,8 @@ class MySQLDatabase extends Database implements TransactionManager
         // Notify connector of parameters
         $this->connector->connect($parameters);
 
-        // This is important!
-        $this->setSQLMode('ANSI');
+        // Set sql_mode
+        $this->setSQLMode(static::config()->get('sql_mode'));
 
         if (isset($parameters['timezone'])) {
             $this->selectTimezone($parameters['timezone']);