Update doc dql-custom-walkers.rst with an output walker to interpolate parameters into SQL

docs/en/cookbook/dql-custom-walkers.rst

@@ -40,7 +40,8 @@ Now this is all awfully technical, so let me come to some use-cases
 fast to keep you motivated. Using walker implementation you can for
 example:
 
-
+-  Modify the Output walker to get the raw SQL via ``Query->getSQL()``
+   with interpolated parameters.
 -  Modify the AST to generate a Count Query to be used with a
    paginator for any given DQL query.
 -  Modify the Output Walker to generate vendor-specific SQL
@@ -50,7 +51,7 @@ example:
 -  Modify the Output walker to pretty print the SQL for debugging
    purposes.
 
-In this cookbook-entry I will show examples of the first two
+In this cookbook-entry I will show examples of the first three
 points. There are probably much more use-cases.
 
 Generic count query for pagination
@@ -215,3 +216,38 @@ huge benefits with using vendor specific features. This would still
 allow you write DQL queries instead of NativeQueries to make use of
 vendor specific features.
 
+Modifying the Output Walker to get the raw SQL with interpolated parameters
+---------------------------------------------------------------------------
+
+Sometimes we may want to log or trace the raw SQL being generated from its DQL,
+``$query->getSQL()`` will give us the prepared statement being passed to database
+with all values of SQL parameters being replaced by positional ``?`` or named ``:name``
+as parameters are interpolated into prepared statements by the database while executing the SQL.
+``$query->getParameters()`` will give us details about SQL parameters that we've provided.
+So we can create an output walker to interpolate all SQL parameters that will be
+passed into prepared statement in PHP before database handle them internally:
+
+.. literalinclude:: dql-custom-walkers/InterpolateParametersSQLOutputWalker.php
+   :language: php
+
+Then you may get the raw SQL with this output walker:
+
+.. code-block:: php
+
+    <?php
+    $query
+        ->where('t.int IN (:ints)')->setParameter(':ints', [1, 2])
+        ->orWhere('t.string IN (?0)')->setParameter(0, ['3', '4'])
+        ->orWhere("t.bool = ?1")->setParameter('?1', true)
+        ->orWhere("t.string = :string")->setParameter(':string', 'ABC')
+        ->setHint(\Doctrine\ORM\Query::HINT_CUSTOM_OUTPUT_WALKER, InterpolateParametersSQLOutputWalker::class)
+        ->getSQL();
+
+The where clause of the returned SQL should be like:
+
+.. code-block:: sql
+
+    WHERE t0_.int IN (1, 2)
+       OR t0_.string IN ('3', '4')
+       OR t0_.bool = 1
+       OR t0_.string = 'ABC'

docs/en/cookbook/dql-custom-walkers/InterpolateParametersSQLOutputWalker.php

@@ -0,0 +1,47 @@
+<?php
+use Doctrine\DBAL\ArrayParameterType;
+use Doctrine\DBAL\ParameterType;
+use Doctrine\DBAL\Types\BooleanType;
+use Doctrine\DBAL\Types\Exception\ValueNotConvertible;
+use Doctrine\DBAL\Types\Type;
+use Doctrine\ORM\Query\AST;
+use Doctrine\ORM\Query\SqlOutputWalker;
+
+class InterpolateParametersSQLOutputWalker extends SqlOutputWalker
+{
+    /** {@inheritdoc} */
+    public function walkInputParameter(AST\InputParameter $inputParam): string
+    {
+        $parameter = $this->getQuery()->getParameter($inputParam->name);
+        if ($parameter === null) {
+            return '?';
+        }
+
+        $value = $parameter->getValue();
+        /** @var ParameterType|ArrayParameterType|int|string $typeName */
+        /** @see \Doctrine\ORM\Query\ParameterTypeInferer::inferType() */
+        $typeName = $parameter->getType();
+        $platform = $this->getConnection()->getDatabasePlatform();
+        $processParameterType = static fn(ParameterType $type) => static fn($value): string =>
+            (match ($type) { /** @see Type::getBindingType() */
+                ParameterType::NULL => 'NULL',
+                ParameterType::INTEGER => $value,
+                ParameterType::BOOLEAN => (new BooleanType())->convertToDatabaseValue($value, $platform),
+                ParameterType::STRING, ParameterType::ASCII => $platform->quoteStringLiteral($value),
+                default => throw new ValueNotConvertible($value, $type->name)
+            });
+
+        if (is_string($typeName) && Type::hasType($typeName)) {
+            return Type::getType($typeName)->convertToDatabaseValue($value, $platform);
+        }
+        if ($typeName instanceof ParameterType) {
+            return $processParameterType($typeName)($value);
+        }
+        if ($typeName instanceof ArrayParameterType && is_array($value)) {
+            $type = ArrayParameterType::toElementParameterType($typeName);
+            return implode(', ', array_map($processParameterType($type), $value));
+        }
+
+        throw new ValueNotConvertible($value, $typeName);
+    }
+}