Hacks to avoid failure on upgrade due to new field not yet being in the DB

On attempting to upgrade I found I couldn't get to the upgrade screen add the new serialize field as
I got fatal errors in these 2 places (maybe more to come).

The new field is civicrm_custom_field.serialize

CRM/Core/BAO/CustomField.php

@@ -278,6 +278,7 @@ class CRM_Core_BAO_CustomField extends CRM_Core_DAO_CustomField {
    *
    * @return array
    *   an array of active custom fields.
+   * @throws \CRM_Core_Exception
    */
   public static function &getFields(
     $customDataType = 'Individual',
@@ -392,6 +393,10 @@ class CRM_Core_BAO_CustomField extends CRM_Core_DAO_CustomField {
         if ($onlyParent) {
           $extends .= " AND $cgTable.extends_entity_column_value IS NULL AND $cgTable.extends_entity_column_id IS NULL ";
         }
+        // Temporary hack - in 5.27 a new field is added to civicrm_custom_field. There is a high
+        // risk this function is called before the upgrade page can be reached and if
+        // so it will potentially result in fatal error.
+        $serializeField = CRM_Core_BAO_Domain::isDBUpdateRequired() ? '' : "$cfTable.serialize,";
 
         $query = "SELECT $cfTable.id, $cfTable.label,
                             $cgTable.title,
@@ -410,7 +415,7 @@ class CRM_Core_BAO_CustomField extends CRM_Core_DAO_CustomField {
                             $cfTable.date_format,
                             $cfTable.time_format,
                             $cgTable.is_multiple,
-                            $cfTable.serialize,
+                            $serializeField
                             $cgTable.table_name,
                             og.name as option_group_name
                      FROM $cfTable

CRM/Core/BAO/Domain.php

@@ -82,6 +82,19 @@ class CRM_Core_BAO_Domain extends CRM_Core_DAO_Domain {
     );
   }
 
+  /**
+   * Is a database update required to apply latest schema changes.
+   *
+   * @return bool
+   *
+   * @throws \CRM_Core_Exception
+   */
+  public static function isDBUpdateRequired() {
+    $dbVersion = CRM_Core_BAO_Domain::version();
+    $codeVersion = CRM_Utils_System::version();
+    return version_compare($dbVersion, $codeVersion) < 0;
+  }
+
   /**
    * Get the location values of a domain.
    *

CRM/Utils/Check/Component/Env.php

@@ -739,10 +739,8 @@ class CRM_Utils_Check_Component_Env extends CRM_Utils_Check_Component {
       );
     }
     else {
-      $codeVersion = CRM_Utils_System::version();
-
       // if db.ver < code.ver, time to upgrade
-      if (version_compare($dbVersion, $codeVersion) < 0) {
+      if (CRM_Core_BAO_Domain::isDBUpdateRequired()) {
         $messages[] = new CRM_Utils_Check_Message(
           __FUNCTION__,
           ts('New codebase version detected. You must visit <a href=\'%1\'>upgrade screen</a> to upgrade the database.', [1 => $upgradeUrl]),

CRM/Utils/Check/Component/Schema.php

@@ -94,6 +94,10 @@ class CRM_Utils_Check_Component_Schema extends CRM_Utils_Check_Component {
    * @return array
    */
   public function checkSmartGroupCustomFieldCriteria() {
+    if (CRM_Core_BAO_Domain::isDBUpdateRequired()) {
+      // Do not run this check when the db has not been updated as it might fail on non-updated schema issues.
+      return [];
+    }
     $messages = $problematicSG = [];
     $customFieldIds = array_keys(CRM_Core_BAO_CustomField::getFields('ANY', FALSE, FALSE, NULL, NULL, FALSE, FALSE, FALSE));
     try {

api/v3/CustomField.php

@@ -122,7 +122,7 @@ function civicrm_api3_custom_field_delete($params) {
  * @return array
  */
 function civicrm_api3_custom_field_get($params) {
-  if (($params['legacy_html_type'] ?? TRUE) && !empty($params['return'])) {
+  if (!CRM_Core_BAO_Domain::isDBUpdateRequired() && ($params['legacy_html_type'] ?? TRUE) && !empty($params['return'])) {
     if (is_array($params['return'])) {
       $params['return'][] = 'serialize';
     }