diff --git a/UPGRADE.md b/UPGRADE.md
index f258faa9a07..1c1c17fb04e 100644
--- a/UPGRADE.md
+++ b/UPGRADE.md
@@ -8,6 +8,18 @@ awareness about deprecated code.
 
 # Upgrade to 4.0
 
+## BC BREAK: converted enum-like classes to enums
+
+The following classes have been converted to enums:
+
+1. `Doctrine\DBAL\ColumnCase`,
+2. `Doctrine\DBAL\LockMode`,
+3. `Doctrine\DBAL\TransactionIsolationLevel`,
+4. `Doctrine\DBAL\Platforms\DateIntervalUnit`,
+5. `Doctrine\DBAL\Platforms\TrimMode`.
+
+The corresponding class constants are now instances of their enum type.
+
 ## BC BREAK: renamed SQLite platform classes
 
 1. `SqlitePlatform` => `SQLitePlatform`
diff --git a/src/ColumnCase.php b/src/ColumnCase.php
index e3a19b05a47..687a04f80e6 100644
--- a/src/ColumnCase.php
+++ b/src/ColumnCase.php
@@ -7,24 +7,15 @@
 /**
  * Contains portable column case conversions.
  */
-final class ColumnCase
+enum ColumnCase
 {
     /**
      * Convert column names to upper case.
      */
-    public const UPPER = 1;
+    case UPPER;
 
     /**
      * Convert column names to lower case.
      */
-    public const LOWER = 2;
-
-    /**
-     * This class cannot be instantiated.
-     *
-     * @codeCoverageIgnore
-     */
-    private function __construct()
-    {
-    }
+    case LOWER;
 }
diff --git a/src/Connection.php b/src/Connection.php
index faebaeeb2f6..7c313068ae6 100644
--- a/src/Connection.php
+++ b/src/Connection.php
@@ -96,10 +96,8 @@ class Connection implements ServerVersionProvider
 
     /**
      * The currently active transaction isolation level or NULL before it has been determined.
-     *
-     * @var TransactionIsolationLevel::*|null
      */
-    private ?int $transactionIsolationLevel = null;
+    private ?TransactionIsolationLevel $transactionIsolationLevel = null;
 
     /**
      * The parameters used during creation of the Connection instance.
@@ -501,11 +499,11 @@ public function close(): void
     /**
      * Sets the transaction isolation level.
      *
-     * @param TransactionIsolationLevel::* $level The level to set.
+     * @param TransactionIsolationLevel $level The level to set.
      *
      * @throws Exception
      */
-    public function setTransactionIsolation(int $level): void
+    public function setTransactionIsolation(TransactionIsolationLevel $level): void
     {
         $this->transactionIsolationLevel = $level;
 
@@ -515,11 +513,11 @@ public function setTransactionIsolation(int $level): void
     /**
      * Gets the currently active transaction isolation level.
      *
-     * @return TransactionIsolationLevel::* The current transaction isolation level.
+     * @return TransactionIsolationLevel The current transaction isolation level.
      *
      * @throws Exception
      */
-    public function getTransactionIsolation(): int
+    public function getTransactionIsolation(): TransactionIsolationLevel
     {
         return $this->transactionIsolationLevel ??= $this->getDatabasePlatform()->getDefaultTransactionIsolationLevel();
     }
diff --git a/src/Exception/InvalidLockMode.php b/src/Exception/InvalidLockMode.php
deleted file mode 100644
index 64e96201ab7..00000000000
--- a/src/Exception/InvalidLockMode.php
+++ /dev/null
@@ -1,26 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-namespace Doctrine\DBAL\Exception;
-
-use Doctrine\DBAL\Exception;
-
-use function sprintf;
-
-/**
- * @psalm-immutable
- */
-class InvalidLockMode extends Exception
-{
-    public static function fromLockMode(int $lockMode): self
-    {
-        return new self(
-            sprintf(
-                'Lock mode %d is invalid. The valid values are LockMode::NONE, LockMode::OPTIMISTIC'
-                    . ', LockMode::PESSIMISTIC_READ and LockMode::PESSIMISTIC_WRITE',
-                $lockMode
-            )
-        );
-    }
-}
diff --git a/src/LockMode.php b/src/LockMode.php
index e8fa9e2720e..035353e020e 100644
--- a/src/LockMode.php
+++ b/src/LockMode.php
@@ -5,21 +5,12 @@
 namespace Doctrine\DBAL;
 
 /**
- * Contains all DBAL LockModes.
+ * Contains all supported lock modes.
  */
-class LockMode
+enum LockMode
 {
-    final public const NONE              = 0;
-    final public const OPTIMISTIC        = 1;
-    final public const PESSIMISTIC_READ  = 2;
-    final public const PESSIMISTIC_WRITE = 4;
-
-    /**
-     * Private constructor. This class cannot be instantiated.
-     *
-     * @codeCoverageIgnore
-     */
-    final private function __construct()
-    {
-    }
+    case NONE;
+    case OPTIMISTIC;
+    case PESSIMISTIC_READ;
+    case PESSIMISTIC_WRITE;
 }
diff --git a/src/Platforms/AbstractMySQLPlatform.php b/src/Platforms/AbstractMySQLPlatform.php
index 3f364b42f5c..30c25805c07 100644
--- a/src/Platforms/AbstractMySQLPlatform.php
+++ b/src/Platforms/AbstractMySQLPlatform.php
@@ -85,11 +85,11 @@ protected function getDateArithmeticIntervalExpression(
         string $date,
         string $operator,
         string $interval,
-        string $unit
+        DateIntervalUnit $unit
     ): string {
         $function = $operator === '+' ? 'DATE_ADD' : 'DATE_SUB';
 
-        return $function . '(' . $date . ', INTERVAL ' . $interval . ' ' . $unit . ')';
+        return $function . '(' . $date . ', INTERVAL ' . $interval . ' ' . $unit->value . ')';
     }
 
     public function getDateDiffExpression(string $date1, string $date2): string
@@ -677,7 +677,7 @@ public function getDropUniqueConstraintSQL(string $name, string $tableName): str
         return $this->getDropIndexSQL($name, $tableName);
     }
 
-    public function getSetTransactionIsolationSQL(int $level): string
+    public function getSetTransactionIsolationSQL(TransactionIsolationLevel $level): string
     {
         return 'SET SESSION TRANSACTION ISOLATION LEVEL ' . $this->_getTransactionIsolationLevelSQL($level);
     }
@@ -778,7 +778,7 @@ public function quoteStringLiteral(string $str): string
         return parent::quoteStringLiteral($str);
     }
 
-    public function getDefaultTransactionIsolationLevel(): int
+    public function getDefaultTransactionIsolationLevel(): TransactionIsolationLevel
     {
         return TransactionIsolationLevel::REPEATABLE_READ;
     }
diff --git a/src/Platforms/AbstractPlatform.php b/src/Platforms/AbstractPlatform.php
index c4f54f2134e..9afde034342 100644
--- a/src/Platforms/AbstractPlatform.php
+++ b/src/Platforms/AbstractPlatform.php
@@ -17,7 +17,6 @@
 use Doctrine\DBAL\Events;
 use Doctrine\DBAL\Exception;
 use Doctrine\DBAL\Exception\ColumnLengthRequired;
-use Doctrine\DBAL\Exception\InvalidLockMode;
 use Doctrine\DBAL\LockMode;
 use Doctrine\DBAL\Platforms\Exception\NoColumnsSpecifiedForTable;
 use Doctrine\DBAL\Platforms\Exception\NotSupported;
@@ -418,12 +417,10 @@ public function getModExpression(string $dividend, string $divisor): string
      * Returns the SQL snippet to trim a string.
      *
      * @param string      $str  The expression to apply the trim to.
-     * @param int         $mode The position of the trim (leading/trailing/both).
+     * @param TrimMode    $mode The position of the trim.
      * @param string|null $char The char to trim, has to be quoted already. Defaults to space.
-     *
-     * @throws InvalidArgumentException
      */
-    public function getTrimExpression(string $str, int $mode = TrimMode::UNSPECIFIED, ?string $char = null): string
+    public function getTrimExpression(string $str, TrimMode $mode = TrimMode::UNSPECIFIED, ?string $char = null): string
     {
         $tokens = [];
 
@@ -442,14 +439,6 @@ public function getTrimExpression(string $str, int $mode = TrimMode::UNSPECIFIED
             case TrimMode::BOTH:
                 $tokens[] = 'BOTH';
                 break;
-
-            default:
-                throw new InvalidArgumentException(
-                    sprintf(
-                        'The value of $mode is expected to be one of the TrimMode constants, %d given.',
-                        $mode
-                    )
-                );
         }
 
         if ($char !== null) {
@@ -688,18 +677,18 @@ public function getDateSubYearsExpression(string $date, string $years): string
     /**
      * Returns the SQL for a date arithmetic expression.
      *
-     * @param string $date     SQL expression representing a date to perform the arithmetic operation on.
-     * @param string $operator The arithmetic operator (+ or -).
-     * @param string $interval SQL expression representing the value of the interval that shall be calculated
-     *                         into the date.
-     * @param string $unit     The unit of the interval that shall be calculated into the date.
+     * @param string           $date     SQL expression representing a date to perform the arithmetic operation on.
+     * @param string           $operator The arithmetic operator (+ or -).
+     * @param string           $interval SQL expression representing the value of the interval that shall be calculated
+     *                                   into the date.
+     * @param DateIntervalUnit $unit     The unit of the interval that shall be calculated into the date.
      *                         One of the DATE_INTERVAL_UNIT_* constants.
      */
     abstract protected function getDateArithmeticIntervalExpression(
         string $date,
         string $operator,
         string $interval,
-        string $unit
+        DateIntervalUnit $unit
     ): string;
 
     /**
@@ -753,18 +742,10 @@ public function getForUpdateSQL(): string
      * ANSI SQL FOR UPDATE specification.
      *
      * @param string $fromClause The FROM clause to append the hint for the given lock mode to
-     * @param int    $lockMode   One of the Doctrine\DBAL\LockMode::* constants
-     * @psalm-param LockMode::* $lockMode
      */
-    public function appendLockHint(string $fromClause, int $lockMode): string
+    public function appendLockHint(string $fromClause, LockMode $lockMode): string
     {
-        return match ($lockMode) {
-            LockMode::NONE,
-            LockMode::OPTIMISTIC,
-            LockMode::PESSIMISTIC_READ,
-            LockMode::PESSIMISTIC_WRITE => $fromClause,
-            default => throw InvalidLockMode::fromLockMode($lockMode),
-        };
+        return $fromClause;
     }
 
     /**
@@ -1992,17 +1973,14 @@ public function getCurrentTimestampSQL(): string
 
     /**
      * Returns the SQL for a given transaction isolation level Connection constant.
-     *
-     * @throws InvalidArgumentException
      */
-    protected function _getTransactionIsolationLevelSQL(int $level): string
+    protected function _getTransactionIsolationLevelSQL(TransactionIsolationLevel $level): string
     {
         return match ($level) {
             TransactionIsolationLevel::READ_UNCOMMITTED => 'READ UNCOMMITTED',
             TransactionIsolationLevel::READ_COMMITTED => 'READ COMMITTED',
             TransactionIsolationLevel::REPEATABLE_READ => 'REPEATABLE READ',
             TransactionIsolationLevel::SERIALIZABLE => 'SERIALIZABLE',
-            default => throw new InvalidArgumentException(sprintf('Invalid isolation level "%s".', $level)),
         };
     }
 
@@ -2068,7 +2046,7 @@ public function getDropDatabaseSQL(string $name): string
     /**
      * Returns the SQL to set the transaction isolation level.
      */
-    abstract public function getSetTransactionIsolationSQL(int $level): string;
+    abstract public function getSetTransactionIsolationSQL(TransactionIsolationLevel $level): string;
 
     /**
      * Obtains DBMS specific SQL to be used to create datetime columns in
@@ -2115,11 +2093,9 @@ public function getFloatDeclarationSQL(array $column): string
     /**
      * Gets the default transaction isolation level of the platform.
      *
-     * @see TransactionIsolationLevel
-     *
-     * @return TransactionIsolationLevel::* The default isolation level.
+     * @return TransactionIsolationLevel The default isolation level.
      */
-    public function getDefaultTransactionIsolationLevel(): int
+    public function getDefaultTransactionIsolationLevel(): TransactionIsolationLevel
     {
         return TransactionIsolationLevel::READ_COMMITTED;
     }
diff --git a/src/Platforms/DB2Platform.php b/src/Platforms/DB2Platform.php
index 7ee0f41466a..c0ac78b6ea4 100644
--- a/src/Platforms/DB2Platform.php
+++ b/src/Platforms/DB2Platform.php
@@ -14,6 +14,7 @@
 use Doctrine\DBAL\Schema\Identifier;
 use Doctrine\DBAL\Schema\Index;
 use Doctrine\DBAL\Schema\TableDiff;
+use Doctrine\DBAL\TransactionIsolationLevel;
 
 use function array_merge;
 use function count;
@@ -133,7 +134,7 @@ protected function getDateArithmeticIntervalExpression(
         string $date,
         string $operator,
         string $interval,
-        string $unit
+        DateIntervalUnit $unit
     ): string {
         switch ($unit) {
             case DateIntervalUnit::WEEK:
@@ -147,7 +148,7 @@ protected function getDateArithmeticIntervalExpression(
                 break;
         }
 
-        return $date . ' ' . $operator . ' ' . $interval . ' ' . $unit;
+        return $date . ' ' . $operator . ' ' . $interval . ' ' . $unit->value;
     }
 
     public function getDateDiffExpression(string $date1, string $date2): string
@@ -195,7 +196,7 @@ public function getTruncateTableSQL(string $tableName, bool $cascade = false): s
      *
      * @throws Exception
      */
-    public function getSetTransactionIsolationSQL(int $level): string
+    public function getSetTransactionIsolationSQL(TransactionIsolationLevel $level): string
     {
         throw NotSupported::new(__METHOD__);
     }
diff --git a/src/Platforms/DateIntervalUnit.php b/src/Platforms/DateIntervalUnit.php
index c1f3ca59218..ba783f37223 100644
--- a/src/Platforms/DateIntervalUnit.php
+++ b/src/Platforms/DateIntervalUnit.php
@@ -4,28 +4,14 @@
 
 namespace Doctrine\DBAL\Platforms;
 
-final class DateIntervalUnit
+enum DateIntervalUnit: string
 {
-    public const SECOND = 'SECOND';
-
-    public const MINUTE = 'MINUTE';
-
-    public const HOUR = 'HOUR';
-
-    public const DAY = 'DAY';
-
-    public const WEEK = 'WEEK';
-
-    public const MONTH = 'MONTH';
-
-    public const QUARTER = 'QUARTER';
-
-    public const YEAR = 'YEAR';
-
-    /**
-     * @codeCoverageIgnore
-     */
-    private function __construct()
-    {
-    }
+    case SECOND  = 'SECOND';
+    case MINUTE  = 'MINUTE';
+    case HOUR    = 'HOUR';
+    case DAY     = 'DAY';
+    case WEEK    = 'WEEK';
+    case MONTH   = 'MONTH';
+    case QUARTER = 'QUARTER';
+    case YEAR    = 'YEAR';
 }
diff --git a/src/Platforms/OraclePlatform.php b/src/Platforms/OraclePlatform.php
index e9ad5b78cfa..acb0b00cd31 100644
--- a/src/Platforms/OraclePlatform.php
+++ b/src/Platforms/OraclePlatform.php
@@ -55,7 +55,7 @@ protected function getDateArithmeticIntervalExpression(
         string $date,
         string $operator,
         string $interval,
-        string $unit
+        DateIntervalUnit $unit
     ): string {
         switch ($unit) {
             case DateIntervalUnit::MONTH:
@@ -174,18 +174,18 @@ public function getSequenceNextValSQL(string $sequence): string
         return 'SELECT ' . $sequence . '.nextval FROM DUAL';
     }
 
-    public function getSetTransactionIsolationSQL(int $level): string
+    public function getSetTransactionIsolationSQL(TransactionIsolationLevel $level): string
     {
         return 'SET TRANSACTION ISOLATION LEVEL ' . $this->_getTransactionIsolationLevelSQL($level);
     }
 
-    protected function _getTransactionIsolationLevelSQL(int $level): string
+    protected function _getTransactionIsolationLevelSQL(TransactionIsolationLevel $level): string
     {
         return match ($level) {
             TransactionIsolationLevel::READ_UNCOMMITTED => 'READ UNCOMMITTED',
             TransactionIsolationLevel::READ_COMMITTED => 'READ COMMITTED',
-            TransactionIsolationLevel::REPEATABLE_READ, TransactionIsolationLevel::SERIALIZABLE => 'SERIALIZABLE',
-            default => parent::_getTransactionIsolationLevelSQL($level),
+            TransactionIsolationLevel::REPEATABLE_READ,
+            TransactionIsolationLevel::SERIALIZABLE => 'SERIALIZABLE',
         };
     }
 
diff --git a/src/Platforms/PostgreSQLPlatform.php b/src/Platforms/PostgreSQLPlatform.php
index 3610cee8476..b1740a77e1f 100644
--- a/src/Platforms/PostgreSQLPlatform.php
+++ b/src/Platforms/PostgreSQLPlatform.php
@@ -14,6 +14,7 @@
 use Doctrine\DBAL\Schema\PostgreSQLSchemaManager;
 use Doctrine\DBAL\Schema\Sequence;
 use Doctrine\DBAL\Schema\TableDiff;
+use Doctrine\DBAL\TransactionIsolationLevel;
 use Doctrine\DBAL\Types\BinaryType;
 use Doctrine\DBAL\Types\BlobType;
 use UnexpectedValueException;
@@ -94,14 +95,14 @@ protected function getDateArithmeticIntervalExpression(
         string $date,
         string $operator,
         string $interval,
-        string $unit
+        DateIntervalUnit $unit
     ): string {
         if ($unit === DateIntervalUnit::QUARTER) {
             $interval = $this->multiplyInterval($interval, 3);
             $unit     = DateIntervalUnit::MONTH;
         }
 
-        return '(' . $date . ' ' . $operator . ' (' . $interval . " || ' " . $unit . "')::interval)";
+        return '(' . $date . ' ' . $operator . ' (' . $interval . " || ' " . $unit->value . "')::interval)";
     }
 
     public function getDateDiffExpression(string $date1, string $date2): string
@@ -608,7 +609,7 @@ public function getSequenceNextValSQL(string $sequence): string
         return "SELECT NEXTVAL('" . $sequence . "')";
     }
 
-    public function getSetTransactionIsolationSQL(int $level): string
+    public function getSetTransactionIsolationSQL(TransactionIsolationLevel $level): string
     {
         return 'SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL '
             . $this->_getTransactionIsolationLevelSQL($level);
diff --git a/src/Platforms/SQLServerPlatform.php b/src/Platforms/SQLServerPlatform.php
index 416dc84558f..f858e6d580e 100644
--- a/src/Platforms/SQLServerPlatform.php
+++ b/src/Platforms/SQLServerPlatform.php
@@ -6,7 +6,6 @@
 
 use Doctrine\DBAL\Connection;
 use Doctrine\DBAL\Exception\ColumnLengthRequired;
-use Doctrine\DBAL\Exception\InvalidLockMode;
 use Doctrine\DBAL\LockMode;
 use Doctrine\DBAL\Platforms\Keywords\KeywordList;
 use Doctrine\DBAL\Platforms\Keywords\SQLServerKeywords;
@@ -17,6 +16,7 @@
 use Doctrine\DBAL\Schema\Sequence;
 use Doctrine\DBAL\Schema\SQLServerSchemaManager;
 use Doctrine\DBAL\Schema\TableDiff;
+use Doctrine\DBAL\TransactionIsolationLevel;
 use InvalidArgumentException;
 
 use function array_merge;
@@ -27,7 +27,6 @@
 use function dechex;
 use function explode;
 use function implode;
-use function in_array;
 use function is_array;
 use function is_bool;
 use function is_numeric;
@@ -72,7 +71,7 @@ protected function getDateArithmeticIntervalExpression(
         string $date,
         string $operator,
         string $interval,
-        string $unit
+        DateIntervalUnit $unit
     ): string {
         $factorClause = '';
 
@@ -80,7 +79,7 @@ protected function getDateArithmeticIntervalExpression(
             $factorClause = '-1 * ';
         }
 
-        return 'DATEADD(' . $unit . ', ' . $factorClause . $interval . ', ' . $date . ')';
+        return 'DATEADD(' . $unit->value . ', ' . $factorClause . $interval . ', ' . $date . ')';
     }
 
     public function getDateDiffExpression(string $date1, string $date2): string
@@ -791,14 +790,8 @@ public function getModExpression(string $dividend, string $divisor): string
         return $dividend . ' % ' . $divisor;
     }
 
-    public function getTrimExpression(string $str, int $mode = TrimMode::UNSPECIFIED, ?string $char = null): string
+    public function getTrimExpression(string $str, TrimMode $mode = TrimMode::UNSPECIFIED, ?string $char = null): string
     {
-        if (! in_array($mode, [TrimMode::UNSPECIFIED, TrimMode::LEADING, TrimMode::TRAILING, TrimMode::BOTH], true)) {
-            throw new InvalidArgumentException(
-                sprintf('The value of $mode is expected to be one of the TrimMode constants, %d given', $mode)
-            );
-        }
-
         if ($char === null) {
             return match ($mode) {
                 TrimMode::LEADING => 'LTRIM(' . $str . ')',
@@ -852,7 +845,7 @@ public function getCurrentDatabaseExpression(): string
         return 'DB_NAME()';
     }
 
-    public function getSetTransactionIsolationSQL(int $level): string
+    public function getSetTransactionIsolationSQL(TransactionIsolationLevel $level): string
     {
         return 'SET TRANSACTION ISOLATION LEVEL ' . $this->_getTransactionIsolationLevelSQL($level);
     }
@@ -1125,14 +1118,13 @@ public function getForeignKeyReferentialActionSQL(string $action): string
         return parent::getForeignKeyReferentialActionSQL($action);
     }
 
-    public function appendLockHint(string $fromClause, int $lockMode): string
+    public function appendLockHint(string $fromClause, LockMode $lockMode): string
     {
         return match ($lockMode) {
             LockMode::NONE,
             LockMode::OPTIMISTIC => $fromClause,
             LockMode::PESSIMISTIC_READ => $fromClause . ' WITH (HOLDLOCK, ROWLOCK)',
             LockMode::PESSIMISTIC_WRITE => $fromClause . ' WITH (UPDLOCK, ROWLOCK)',
-            default => throw InvalidLockMode::fromLockMode($lockMode),
         };
     }
 
diff --git a/src/Platforms/SQLitePlatform.php b/src/Platforms/SQLitePlatform.php
index 9f4208b761d..c962ef8c41c 100644
--- a/src/Platforms/SQLitePlatform.php
+++ b/src/Platforms/SQLitePlatform.php
@@ -19,7 +19,6 @@
 use Doctrine\DBAL\Schema\TableDiff;
 use Doctrine\DBAL\TransactionIsolationLevel;
 use Doctrine\DBAL\Types;
-use InvalidArgumentException;
 
 use function array_combine;
 use function array_keys;
@@ -60,19 +59,13 @@ public function getRegexpExpression(): string
         return 'REGEXP';
     }
 
-    public function getTrimExpression(string $str, int $mode = TrimMode::UNSPECIFIED, ?string $char = null): string
+    public function getTrimExpression(string $str, TrimMode $mode = TrimMode::UNSPECIFIED, ?string $char = null): string
     {
         $trimFn = match ($mode) {
             TrimMode::UNSPECIFIED,
             TrimMode::BOTH => 'TRIM',
             TrimMode::LEADING => 'LTRIM',
             TrimMode::TRAILING => 'RTRIM',
-            default => throw new InvalidArgumentException(
-                sprintf(
-                    'The value of $mode is expected to be one of the TrimMode constants, %d given.',
-                    $mode
-                )
-            ),
         };
 
         $arguments = [$str];
@@ -106,7 +99,7 @@ protected function getDateArithmeticIntervalExpression(
         string $date,
         string $operator,
         string $interval,
-        string $unit
+        DateIntervalUnit $unit
     ): string {
         switch ($unit) {
             case DateIntervalUnit::WEEK:
@@ -123,7 +116,7 @@ protected function getDateArithmeticIntervalExpression(
         return 'DATETIME(' . $date . ',' . $this->getConcatExpression(
             $this->quoteStringLiteral($operator),
             $interval,
-            $this->quoteStringLiteral(' ' . $unit)
+            $this->quoteStringLiteral(' ' . $unit->value)
         ) . ')';
     }
 
@@ -145,18 +138,17 @@ public function getCurrentDatabaseExpression(): string
         return "''";
     }
 
-    protected function _getTransactionIsolationLevelSQL(int $level): string
+    protected function _getTransactionIsolationLevelSQL(TransactionIsolationLevel $level): string
     {
         return match ($level) {
             TransactionIsolationLevel::READ_UNCOMMITTED => '0',
             TransactionIsolationLevel::READ_COMMITTED,
             TransactionIsolationLevel::REPEATABLE_READ,
             TransactionIsolationLevel::SERIALIZABLE => '1',
-            default => parent::_getTransactionIsolationLevelSQL($level),
         };
     }
 
-    public function getSetTransactionIsolationSQL(int $level): string
+    public function getSetTransactionIsolationSQL(TransactionIsolationLevel $level): string
     {
         return 'PRAGMA read_uncommitted = ' . $this->_getTransactionIsolationLevelSQL($level);
     }
diff --git a/src/Platforms/TrimMode.php b/src/Platforms/TrimMode.php
index eb499ee4621..31c237543fc 100644
--- a/src/Platforms/TrimMode.php
+++ b/src/Platforms/TrimMode.php
@@ -4,20 +4,10 @@
 
 namespace Doctrine\DBAL\Platforms;
 
-final class TrimMode
+enum TrimMode
 {
-    public const UNSPECIFIED = 0;
-
-    public const LEADING = 1;
-
-    public const TRAILING = 2;
-
-    public const BOTH = 3;
-
-    /**
-     * @codeCoverageIgnore
-     */
-    private function __construct()
-    {
-    }
+    case UNSPECIFIED;
+    case LEADING;
+    case TRAILING;
+    case BOTH;
 }
diff --git a/src/Portability/Driver.php b/src/Portability/Driver.php
index a90c64b0b89..831fd4a514f 100644
--- a/src/Portability/Driver.php
+++ b/src/Portability/Driver.php
@@ -15,7 +15,7 @@
 
 final class Driver extends AbstractDriverMiddleware
 {
-    public function __construct(DriverInterface $driver, private readonly int $mode, private readonly int $case)
+    public function __construct(DriverInterface $driver, private readonly int $mode, private readonly ?ColumnCase $case)
     {
         parent::__construct($driver);
     }
@@ -34,14 +34,17 @@ public function connect(array $params): ConnectionInterface
 
         $case = null;
 
-        if ($this->case !== 0 && ($portability & Connection::PORTABILITY_FIX_CASE) !== 0) {
+        if ($this->case !== null && ($portability & Connection::PORTABILITY_FIX_CASE) !== 0) {
             $nativeConnection = $connection->getNativeConnection();
 
+            $case = match ($this->case) {
+                ColumnCase::LOWER => CASE_LOWER,
+                ColumnCase::UPPER => CASE_UPPER,
+            };
+
             if ($nativeConnection instanceof PDO) {
                 $portability &= ~Connection::PORTABILITY_FIX_CASE;
-                $nativeConnection->setAttribute(PDO::ATTR_CASE, $this->case);
-            } else {
-                $case = $this->case === ColumnCase::LOWER ? CASE_LOWER : CASE_UPPER;
+                $nativeConnection->setAttribute(PDO::ATTR_CASE, $case);
             }
         }
 
diff --git a/src/Portability/Middleware.php b/src/Portability/Middleware.php
index c4053f60162..b97897c978d 100644
--- a/src/Portability/Middleware.php
+++ b/src/Portability/Middleware.php
@@ -4,12 +4,13 @@
 
 namespace Doctrine\DBAL\Portability;
 
+use Doctrine\DBAL\ColumnCase;
 use Doctrine\DBAL\Driver as DriverInterface;
 use Doctrine\DBAL\Driver\Middleware as MiddlewareInterface;
 
 final class Middleware implements MiddlewareInterface
 {
-    public function __construct(private readonly int $mode, private readonly int $case)
+    public function __construct(private readonly int $mode, private readonly ?ColumnCase $case)
     {
     }
 
diff --git a/src/TransactionIsolationLevel.php b/src/TransactionIsolationLevel.php
index e8dc5d91814..2b094dbe84e 100644
--- a/src/TransactionIsolationLevel.php
+++ b/src/TransactionIsolationLevel.php
@@ -4,32 +4,10 @@
 
 namespace Doctrine\DBAL;
 
-final class TransactionIsolationLevel
+enum TransactionIsolationLevel
 {
-    /**
-     * Transaction isolation level READ UNCOMMITTED.
-     */
-    public const READ_UNCOMMITTED = 1;
-
-    /**
-     * Transaction isolation level READ COMMITTED.
-     */
-    public const READ_COMMITTED = 2;
-
-    /**
-     * Transaction isolation level REPEATABLE READ.
-     */
-    public const REPEATABLE_READ = 3;
-
-    /**
-     * Transaction isolation level SERIALIZABLE.
-     */
-    public const SERIALIZABLE = 4;
-
-    /**
-     * @codeCoverageIgnore
-     */
-    private function __construct()
-    {
-    }
+    case READ_UNCOMMITTED;
+    case READ_COMMITTED;
+    case REPEATABLE_READ;
+    case SERIALIZABLE;
 }
diff --git a/tests/Functional/DataAccessTest.php b/tests/Functional/DataAccessTest.php
index c85ff547511..c5f27f954df 100644
--- a/tests/Functional/DataAccessTest.php
+++ b/tests/Functional/DataAccessTest.php
@@ -14,7 +14,6 @@
 use Doctrine\DBAL\Statement;
 use Doctrine\DBAL\Tests\FunctionalTestCase;
 use Doctrine\DBAL\Types\Types;
-use InvalidArgumentException;
 
 use function array_change_key_case;
 use function date;
@@ -330,10 +329,10 @@ public function testNativeArrayListSupport(): void
     /**
      * @dataProvider getTrimExpressionData
      */
-    public function testTrimExpression(string $value, int $position, ?string $char, string $expectedResult): void
+    public function testTrimExpression(string $value, TrimMode $mode, ?string $char, string $expectedResult): void
     {
         $sql = 'SELECT ' .
-            $this->connection->getDatabasePlatform()->getTrimExpression($value, $position, $char) . ' AS trimmed ' .
+            $this->connection->getDatabasePlatform()->getTrimExpression($value, $mode, $char) . ' AS trimmed ' .
             'FROM fetch_table';
 
         $row = $this->connection->fetchAssociative($sql);
@@ -388,12 +387,6 @@ public static function getTrimExpressionData(): iterable
         ];
     }
 
-    public function testTrimExpressionInvalidMode(): void
-    {
-        $this->expectException(InvalidArgumentException::class);
-        $this->connection->getDatabasePlatform()->getTrimExpression('Trim me!', 0xBEEF);
-    }
-
     /**
      * @dataProvider modeProvider
      */
diff --git a/tests/Functional/PortabilityTest.php b/tests/Functional/PortabilityTest.php
index 9fe1a9c6ed2..985a3d9bd67 100644
--- a/tests/Functional/PortabilityTest.php
+++ b/tests/Functional/PortabilityTest.php
@@ -52,7 +52,7 @@ public function testFullFetchMode(): void
      *
      * @dataProvider caseProvider
      */
-    public function testCaseConversion(int $case, array $expected): void
+    public function testCaseConversion(ColumnCase $case, array $expected): void
     {
         $this->connectWithPortability(Connection::PORTABILITY_FIX_CASE, $case);
         $this->createTable();
@@ -64,7 +64,7 @@ public function testCaseConversion(int $case, array $expected): void
     }
 
     /**
-     * @return iterable<string, array{int, list<string>}>
+     * @return iterable<string, array{ColumnCase, list<string>}>
      */
     public static function caseProvider(): iterable
     {
@@ -106,7 +106,7 @@ public function assertFetchResultRow(array $row): void
      */
     public function testFetchColumn(string $column, array $expected): void
     {
-        $this->connectWithPortability(Connection::PORTABILITY_RTRIM, 0);
+        $this->connectWithPortability(Connection::PORTABILITY_RTRIM, null);
         $this->createTable();
 
         $result = $this->connection->executeQuery('SELECT ' . $column . ' FROM portability_table');
@@ -133,7 +133,7 @@ public static function fetchColumnProvider(): iterable
 
     public function testFetchAllNullColumn(): void
     {
-        $this->connectWithPortability(Connection::PORTABILITY_EMPTY_TO_NULL, 0);
+        $this->connectWithPortability(Connection::PORTABILITY_EMPTY_TO_NULL, null);
         $this->createTable();
 
         $column = $this->connection->fetchFirstColumn('SELECT Test_Null FROM portability_table');
@@ -141,7 +141,7 @@ public function testFetchAllNullColumn(): void
         self::assertSame([null, null], $column);
     }
 
-    private function connectWithPortability(int $mode, int $case): void
+    private function connectWithPortability(int $mode, ?ColumnCase $case): void
     {
         // closing the default connection prior to 4.0.0 to prevent connection leak
         $this->connection->close();
diff --git a/tests/Platforms/AbstractPlatformTestCase.php b/tests/Platforms/AbstractPlatformTestCase.php
index 250111e858f..e48ca40b4f1 100644
--- a/tests/Platforms/AbstractPlatformTestCase.php
+++ b/tests/Platforms/AbstractPlatformTestCase.php
@@ -7,7 +7,6 @@
 use Doctrine\Common\EventManager;
 use Doctrine\DBAL\Events;
 use Doctrine\DBAL\Exception;
-use Doctrine\DBAL\Exception\InvalidLockMode;
 use Doctrine\DBAL\Platforms\AbstractPlatform;
 use Doctrine\DBAL\Schema\Column;
 use Doctrine\DBAL\Schema\ColumnDiff;
@@ -1368,12 +1367,6 @@ public function asciiStringSqlDeclarationDataProvider(): array
             ['CHAR(12)', ['length' => 12, 'fixed' => true]],
         ];
     }
-
-    public function testInvalidLockMode(): void
-    {
-        $this->expectException(InvalidLockMode::class);
-        $this->platform->appendLockHint('TABLE', 128);
-    }
 }
 
 interface GetCreateTableSqlDispatchEventListener
diff --git a/tests/Platforms/SQLServerPlatformTestCase.php b/tests/Platforms/SQLServerPlatformTestCase.php
index 5798a1c9358..b2884c505c1 100644
--- a/tests/Platforms/SQLServerPlatformTestCase.php
+++ b/tests/Platforms/SQLServerPlatformTestCase.php
@@ -1683,11 +1683,9 @@ public function testAlterTableWithSchemaSameColumnComments(): void
     }
 
     /**
-     * @psalm-param LockMode::* $lockMode
-     *
      * @dataProvider getLockHints
      */
-    public function testAppendsLockHint(int $lockMode, string $lockHint): void
+    public function testAppendsLockHint(LockMode $lockMode, string $lockHint): void
     {
         $fromClause     = 'FROM users';
         $expectedResult = $fromClause . $lockHint;
@@ -1696,7 +1694,7 @@ public function testAppendsLockHint(int $lockMode, string $lockHint): void
     }
 
     /**
-     * @return mixed[][]
+     * @return iterable<int, array{LockMode, string}>
      */
     public static function getLockHints(): iterable
     {