Implement the ability for user-defined type casting

docs/guide/en/README.md

@@ -137,6 +137,7 @@ via schema:
 
 - [Reading database schema](schema/usage.md)
 - [Configuring schema cache](schema/cache.md)
+- [Casting values](schema/typecasting.md)
 
 ## Extensions
 

docs/guide/en/schema/typecasting.md

@@ -0,0 +1,290 @@
+# Type casting values
+
+Type casting is the process of converting a value from one data type to another. In the context of the database,
+type casting is used to ensure that values are saved and retrieved in the correct type.
+
+```mermaid
+flowchart LR
+    phpType[PHP Type]
+    dbType[Database Type]
+
+    phpType --> dbType
+    dbType --> phpType
+```
+
+## Casting values to be saved in the database
+
+When saving a value to the database, the value must be in the correct type. For example, if saving a value to a column
+that is of type `integer`, the value must be an integer.
+
+To ensure that the value is saved in the correct type, `ColumnInterface::dbTypecast()` method can be used to cast 
+the value to the correct type. Majority of the DB library methods, such as `CommandInterface::insert()`, automatically
+cast values to the correct type.
+
+```php
+use Yiisoft\Db\Connection\ConnectionInterface;
+
+/** @var ConnectionInterface $db */
+$command = $db->createCommand();
+$command->insert('customer', [
+    'name' => 'John Doe',
+    'is_active' => true,
+]);
+$command->execute();
+```
+
+In the example above, the value of `is_active` is a `boolean`, but the column `is_active` can be of type `bit`.
+The `CommandInterface::insert()` method will automatically cast the value to the correct type.
+
+## Casting values retrieved from the database
+
+When you retrieve a value from the database, the value can be returned in a different type than you expect.
+For example, a value that is stored as a `float` in the database can be returned as a `string`. This is because 
+the database driver does not convert some data types when retrieves values.
+
+To ensure that the value is returned in the correct type, you can use `ColumnInterface::phpTypecast()` method to cast 
+the value to the correct type.
+
+```php
+use Yiisoft\Db\Connection\ConnectionInterface;
+
+/** @var ConnectionInterface $db */
+$command = $db->createCommand('SELECT * FROM {{customer}} WHERE id = 1');
+
+$row = $command->queryOne();
+$isActive = $row['is_active'];
+
+// Cast the value to the correct type
+$isActive = $db->getTableSchema('customer')->getColumn('is_active')->phpTypecast($isActive);
+```
+
+In the example above, the value of `is_active` can be retrieved from the database as a `bit`, but the correct PHP type 
+is `boolean`. The `ColumnInterface::phpTypecast()` method is used to cast the value to the correct type.
+
+## Custom type casting
+
+To implement custom type casting you need to extend the `AbstractColumnSchema` class and override the `dbTypecast()` 
+and `phpTypecast()` methods.
+
+For example, in Postgres database, the `point` type is represented as a string in the format `(x,y)`. To cast the value
+to a `Point` class, you can create a custom column class and override the `dbTypecast()` and `phpTypecast()`.
+
+```php
+use Yiisoft\Db\Expression\Expression;
+use Yiisoft\Db\Expression\ExpressionInterface;
+use Yiisoft\Db\Schema\AbstractColumnSchema;
+
+class PointColumn extends AbstractColumnSchema
+{
+    /**
+     * @var string The default column abstract type
+     */
+    protected const DEFAULT_TYPE = 'point';
+
+    /**
+    * @param ExpressionInterface|Point|string|null $value
+    */
+    public function dbTypecast(mixed $value): ExpressionInterface|string|null
+    {
+        if ($value instanceof Point) {
+            return new Expression('(:x,:y)', ['x' => $value->getX(), 'y' => $value->getY()]);
+        }
+
+        return $value;
+    }
+
+    /**
+    * @param string|null  $value
+    */
+    public function phpTypecast(mixed $value): Point|null
+    {
+        if (is_string($value)) {
+            [$x, $y] = explode(',', substr($value, 1, -1));
+
+            return new Point((float) $x, (float) $y);
+        }
+
+        return $value;
+    }
+}
+
+class Point
+{
+    public function __construct(
+        private float $x,
+        private float $y,
+    ) {
+    }
+
+    public function getX(): float
+    {
+        return $this->x;
+    }
+
+    public function getY(): float
+    {
+        return $this->y;
+    }
+}
+```
+
+Then use the custom column class in the database connection configuration.
+
+```php
+use Yiisoft\Db\Pgsql\Column\ColumnFactory;
+use Yiisoft\Db\Pgsql\Connection;
+
+$columnFactory = new ColumnFactory(
+    'columnClassMap' => [
+        // It is necessary to define the column class map for the custom abstract type
+        // abstract type => class name
+        'point' => PointColumn::class,
+    ],
+    'typeMap' => [
+        // It is necessary to define the type map for the database type
+        // database type => abstract type
+        'point' => 'point',
+    ],
+);
+
+// Create a database connection with the custom column factory
+$db = new Connection($pdoDriver, $schemaCache, $columnFactory);
+```
+
+In the example above, the `PointColumn` class is used to cast the `point` database type to the `Point` class.
+The `Point` class is used to represent the `point` type as an object with `x` and `y` properties.
+
+## Lazy type casting
+
+Lazy type casting is a way to defer the type casting of a value until it is accessed. This can be useful when you want
+to avoid the overhead of type casting for values that are not used.
+
+Here is an example how to configure lazy type casting for the `array`, `json` and `structured` database types.
+
+```php
+use Yiisoft\Db\Constant\ColumnType;
+use Yiisoft\Db\Pgsql\Column\ColumnFactory;
+use Yiisoft\Db\Pgsql\Connection;
+use Yiisoft\Db\Schema\Column\ArrayLazyColumn;
+use Yiisoft\Db\Schema\Column\StructuredLazyColumn;
+use Yiisoft\Db\Schema\Data\JsonLazyArray;
+
+$columnFactory = new ColumnFactory(
+    'columnClassMap' => [
+        ColumnType::ARRAY => ArrayLazyColumn::class, // converts values to `LazyArray` objects 
+        ColumnType::JSON => JsonLazyColumn::class, // converts values to `JsonLazyArray` objects
+        ColumnType::STRUCTURED => StructuredLazyColumn::class, // converts values to `StructuredLazyArray` objects
+    ],
+);
+
+// Create a database connection with the custom column factory
+$db = new Connection($pdoDriver, $schemaCache, $columnFactory);
+
+/** @var JsonLazyArray $tags `tags` column is of database type `json` */
+$tags = $db->getTableSchema('customer')->getColumn('tags')->phpTypecast($row['tags']);
+
+foreach ($tags as $tag) {
+    echo $tag;
+}
+```
+
+## Structured data types
+
+Some databases support structured data types, such as `composite` types in Postgres. To cast a structured data type to
+a custom class, you need to create a column class which extends `AbstractStructuredColumn` and override 
+the `phpTypecast()` method.
+
+For example if `currency_money` is a defined composite type in Postgres as follows:
+
+```sql
+CREATE TYPE currency_money AS (
+    value DECIMAL(10,2),
+    currency_code CHAR(3)
+);
+```
+
+you can create `MyStructuredColumn` column class to cast the value to `CurrencyMoney` class.
+
+```php
+use Yiisoft\Db\Expression\Expression;
+use Yiisoft\Db\Expression\ExpressionInterface;
+use Yiisoft\Db\Pgsql\Data\StructuredParser;
+
+class MyStructuredColumn extends AbstractStructuredColumn
+{
+    /**
+    * @param string|null $value
+    */
+    public function phpTypecast(mixed $value): CurrencyMoney|StructuredLazyArray|null
+    {
+        if (is_string($value)) {
+            $value = new StructuredLazyArray($value, $this->getColumns());
+
+            return match ($this->getDbType()) {
+                'currency_money' => new CurrencyMoney(...$value->getValue()),
+                default => $value,
+            };
+        }
+
+        return $value;
+    }
+}
+
+class CurrencyMoney implements \JsonSerializable, \IteratorAggregate
+{
+    public function __construct(
+        private float $value,
+        private string $currencyCode = 'USD',
+    ) {
+    }
+
+    public function getCurrencyCode(): string
+    {
+        return $this->currencyCode;
+    }
+
+    public function getValue(): float
+    {
+        return $this->value;
+    }
+
+    /**
+     * `JsonSerializable` interface is implemented to convert the object to a database representation.
+     */
+    public function jsonSerialize(): array
+    {
+        return [
+            'value' => $this->value,
+            'currency_code' => $this->currencyCode,
+        ];
+    }
+
+    /** 
+     * Alternatively, `IteratorAggregate` interface can be implemented to convert the object to a database representation.
+     */
+    public function getIterator(): ArrayIterator
+    {
+        return new ArrayIterator([
+            'value' => $this->value,
+            'currency_code' => $this->currencyCode,
+        ]);
+    } 
+}
+```
+
+Then use the column class in the database connection configuration.
+
+```php
+use Yiisoft\Db\Constant\ColumnType;
+use Yiisoft\Db\Pgsql\Column\ColumnFactory;
+use Yiisoft\Db\Pgsql\Connection;
+
+$columnFactory = new ColumnFactory(
+    'columnClassMap' => [
+        ColumnType::STRUCTURED => MyStructuredColumn::class,
+    ],
+);
+
+// Create a database connection with the custom column factory
+$db = new Connection($pdoDriver, $schemaCache, $columnFactory);
+```

src/Driver/Pdo/AbstractPdoConnection.php

@@ -20,6 +20,7 @@
 use Yiisoft\Db\Profiler\ProfilerAwareInterface;
 use Yiisoft\Db\Profiler\ProfilerAwareTrait;
 use Yiisoft\Db\QueryBuilder\QueryBuilderInterface;
+use Yiisoft\Db\Schema\Column\ColumnFactoryInterface;
 use Yiisoft\Db\Schema\QuoterInterface;
 use Yiisoft\Db\Schema\SchemaInterface;
 use Yiisoft\Db\Transaction\TransactionInterface;
@@ -50,8 +51,11 @@ abstract class AbstractPdoConnection extends AbstractConnection implements PdoCo
     protected QuoterInterface|null $quoter = null;
     protected SchemaInterface|null $schema = null;
 
-    public function __construct(protected PdoDriverInterface $driver, protected SchemaCache $schemaCache)
-    {
+    public function __construct(
+        protected PdoDriverInterface $driver,
+        protected SchemaCache $schemaCache,
+        protected ColumnFactoryInterface|null $columnFactory = null,
+    ) {
     }
 
     /**