indexing virtual fields with dbal

app/config/schema/schema.json

@@ -442,7 +442,8 @@
         "identifiers_i1": { "columns": [ "identifier", "type_id", "person_id" ] },
         "identifiers_i2": { "columns": [ "identifier", "type_id", "external_identity_id" ] },
         "identifiers_i3": { "columns": [ "type_id" ] },
-        "identifiers_i4": { "needed": false, "columns": [ "provisioning_target_id" ] }
+        "identifiers_i4": { "needed": false, "columns": [ "provisioning_target_id" ] },
+        "identifiers_i5": { "columns": [ "lower(identifier)", "type_id" ] }
       },
       "mvea": [ "person", "external_identity", "group" ],
       "sourced": true

app/src/Lib/Util/SchemaManager.php

@@ -261,12 +261,31 @@ protected function processSchema(
           // $flags and $options as passed to Index(), but otherwise undocumented
           $flags = [];
           $options = [];
+
+          // XXX DBAL does not support expression indexes. We will trick DBAL by
+          //     temporary adding the virtual column in the table. This will make
+          //     no difference to the table end result since the actual query list
+          //     will be executed later. What we actually do is treat the expression
+          //     as a temporary virtual column
+          //     https://www.postgresql.org/docs/14/indexes-expressional.html
+          $tempColumns = [];
+          foreach ($iCfg->columns as $clm_name) {
+            if (! $table->hasColumn($clm_name)) {
+              $table->addColumn($clm_name, "string");
+              $tempColumns[] = $clm_name;
+            }
+          }
 
           if(isset($iCfg->unique) && $iCfg->unique) {
             $table->addUniqueConstraint($iCfg->columns, $iName, $flags, $options);
           } else {
             $table->addIndex($iCfg->columns, $iName, $flags, $options);
           }
+
+          foreach ($tempColumns as $clm_name) {
+            $table->dropColumn($clm_name);
+          }
+          $tempColumns = [];
         }
       }