MDL-72184 dml: implement driver methods for casting to char.

lib/dml/moodle_database.php

@@ -2162,6 +2162,17 @@ abstract class moodle_database {
         return ' CEIL(' . $fieldname . ')';
     }
 
+    /**
+     * Return SQL for casting to char of given field/expression. Default implementation performs implicit cast using
+     * concatenation with an empty string
+     *
+     * @param string $field Table field or SQL expression to be cast
+     * @return string
+     */
+    public function sql_cast_to_char(string $field): string {
+        return $this->sql_concat("''", $field);
+    }
+
     /**
      * Returns the SQL to be used in order to CAST one CHAR column to INTEGER.
      *

lib/dml/oci_native_moodle_database.php

@@ -1554,6 +1554,16 @@ class oci_native_moodle_database extends moodle_database {
         return 'MOD(' . $int1 . ', ' . $int2 . ')';
     }
 
+    /**
+     * Return SQL for casting to char of given field/expression
+     *
+     * @param string $field Table field or SQL expression to be cast
+     * @return string
+     */
+    public function sql_cast_to_char(string $field): string {
+        return "TO_CHAR({$field})";
+    }
+
     public function sql_cast_char2int($fieldname, $text=false) {
         if (!$text) {
             return ' CAST(' . $fieldname . ' AS INT) ';

lib/dml/pgsql_native_moodle_database.php

@@ -1453,6 +1453,16 @@ class pgsql_native_moodle_database extends moodle_database {
         return '((' . $int1 . ') # (' . $int2 . '))';
     }
 
+    /**
+     * Return SQL for casting to char of given field/expression
+     *
+     * @param string $field Table field or SQL expression to be cast
+     * @return string
+     */
+    public function sql_cast_to_char(string $field): string {
+        return "CAST({$field} AS VARCHAR)";
+    }
+
     public function sql_cast_char2int($fieldname, $text=false) {
         return ' CAST(' . $fieldname . ' AS INT) ';
     }
@@ -1493,7 +1503,7 @@ class pgsql_native_moodle_database extends moodle_database {
      */
     public function sql_group_concat(string $field, string $separator = ', ', string $sort = ''): string {
         $fieldsort = $sort ? "ORDER BY {$sort}" : '';
-        return "STRING_AGG(CAST({$field} AS VARCHAR), '{$separator}' {$fieldsort})";
+        return "STRING_AGG(" . $this->sql_cast_to_char($field) . ", '{$separator}' {$fieldsort})";
     }
 
     public function sql_regex_supported() {

lib/dml/tests/dml_test.php

@@ -32,6 +32,7 @@ defined('MOODLE_INTERNAL') || die();
  * @subpackage dml
  * @copyright  2008 Nicolas Connault
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ * @coversDefaultClass \moodle_database
  */
 class dml_test extends database_driver_testcase {
 
@@ -501,7 +502,7 @@ SELECT * FROM {users}
 -- line 74 of /lib/dml/tests/fixtures/test_dml_sql_debugging_fixture.php: call to test_dml_sql_debugging_fixture->one()
 -- line 83 of /lib/dml/tests/fixtures/test_dml_sql_debugging_fixture.php: call to test_dml_sql_debugging_fixture->two()
 -- line 92 of /lib/dml/tests/fixtures/test_dml_sql_debugging_fixture.php: call to test_dml_sql_debugging_fixture->three()
--- line 497 of /lib/dml/tests/dml_test.php: call to test_dml_sql_debugging_fixture->four()
+-- line 498 of /lib/dml/tests/dml_test.php: call to test_dml_sql_debugging_fixture->four()
 EOD;
         $this->assertEquals($this->unix_to_os_dirsep($expected), $out);
 
@@ -3840,6 +3841,44 @@ EOD;
         $this->assertEquals(666, $DB->get_field_sql($sql));
     }
 
+    /**
+     * Test DML libraries sql_cast_to_char method
+     *
+     * @covers ::sql_cast_to_char
+     */
+    public function test_cast_to_char(): void {
+        $DB = $this->tdb;
+        $dbman = $DB->get_manager();
+
+        $tableone = $this->get_test_table('one');
+        $tableone->add_field('id', XMLDB_TYPE_INTEGER, '10', null, XMLDB_NOTNULL, XMLDB_SEQUENCE, null);
+        $tableone->add_field('intfield', XMLDB_TYPE_INTEGER, '10', null, XMLDB_NOTNULL, null, null);
+        $tableone->add_field('details', XMLDB_TYPE_CHAR, '255', null, XMLDB_NOTNULL, null, null);
+        $tableone->add_key('primary', XMLDB_KEY_PRIMARY, ['id']);
+        $dbman->create_table($tableone);
+
+        $tableonename = $tableone->getName();
+        $DB->insert_record($tableonename, (object) ['intfield' => 10, 'details' => 'uno']);
+        $DB->insert_record($tableonename, (object) ['intfield' => 20, 'details' => 'dos']);
+
+        $tabletwo = $this->get_test_table('two');
+        $tabletwo->add_field('id', XMLDB_TYPE_INTEGER, '10', null, XMLDB_NOTNULL, XMLDB_SEQUENCE, null);
+        $tabletwo->add_field('charfield', XMLDB_TYPE_CHAR, '255', null, XMLDB_NOTNULL, null, null);
+        $tabletwo->add_key('primary', XMLDB_KEY_PRIMARY, ['id']);
+        $dbman->create_table($tabletwo);
+
+        $tabletwoname = $tabletwo->getName();
+        $DB->insert_record($tabletwoname, (object) ['charfield' => '10']);
+
+        // Test by joining a char field to a cast int field (mixing types not supported across databases).
+        $sql = "SELECT t1.details
+                  FROM {{$tableonename}} t1
+                  JOIN {{$tabletwoname}} t2 ON t2.charfield = " . $DB->sql_cast_to_char('t1.intfield');
+
+        $fieldset = $DB->get_fieldset_sql($sql);
+        $this->assertEquals(['uno'], $fieldset);
+    }
+
     public function test_cast_char2int() {
         $DB = $this->tdb;
         $dbman = $DB->get_manager();

lib/upgrade.txt

@@ -12,6 +12,7 @@ information provided here is intended especially for developers.
   an event exists with the given criteria (see MDL-72723 for details).
    - Breaking: 3rd party log readers implementing interface sql_reader will need to implement get_events_select_exists()
 * Added $strictness parameter to persistent `get_record` method, optionally allowing caller to ensure record exists
+* New DML driver method `$DB->sql_cast_to_char` for casting given field/expression to char
 * For plugins that override secondary navigation, the namespace for the custom secondary navigation class has
   changed. It was (for example) mod_mymodule\local\views\secondary but is now
   mod_mymodule\navigation\views\secondary. The old location will continue to work, but is deprecated.