diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8012aa30d..094958f1c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,7 +2,10 @@
 
 ## 1.1.1 under development
 
-- no changes in this release.
+- Enh #301: Refactor `JsonExpressionBuilder` (@Tigrov)
+- Enh #300: Refactor `ArrayExpressionBuilder` (@Tigrov)
+- Enh #302: Refactor `ColumnSchema` (@Tigrov)
+- Bug #302: Fix incorrect convert string value for BIT type (@Tigrov)
 
 ## 1.1.0 July 24, 2023
 
diff --git a/src/Builder/ArrayExpressionBuilder.php b/src/Builder/ArrayExpressionBuilder.php
index 21a35092e..66b5f634a 100644
--- a/src/Builder/ArrayExpressionBuilder.php
+++ b/src/Builder/ArrayExpressionBuilder.php
@@ -4,7 +4,6 @@
 
 namespace Yiisoft\Db\Pgsql\Builder;
 
-use Traversable;
 use Yiisoft\Db\Exception\Exception;
 use Yiisoft\Db\Exception\InvalidArgumentException;
 use Yiisoft\Db\Exception\InvalidConfigException;
@@ -19,7 +18,7 @@
 
 use function implode;
 use function in_array;
-use function is_array;
+use function is_iterable;
 use function str_repeat;
 
 /**
@@ -34,7 +33,7 @@ public function __construct(private QueryBuilderInterface $queryBuilder)
     /**
      * The Method builds the raw SQL from the expression that won't be additionally escaped or quoted.
      *
-     * @param ExpressionInterface $expression The expression build.
+     * @param ArrayExpression $expression The expression build.
      * @param array $params The binding parameters.
      *
      * @throws Exception
@@ -43,8 +42,6 @@ public function __construct(private QueryBuilderInterface $queryBuilder)
      * @throws NotSupportedException
      *
      * @return string The raw SQL that won't be additionally escaped or quoted.
-     *
-     * @psalm-param ArrayExpression $expression
      */
     public function build(ExpressionInterface $expression, array &$params = []): string
     {
@@ -63,7 +60,7 @@ public function build(ExpressionInterface $expression, array &$params = []): str
         /** @psalm-var string[] $placeholders */
         $placeholders = $this->buildPlaceholders($expression, $params);
 
-        return 'ARRAY[' . implode(', ', $placeholders) . ']' . $this->getTypehint($expression);
+        return 'ARRAY[' . implode(', ', $placeholders) . ']' . $this->getTypeHint($expression);
     }
 
     /**
@@ -75,22 +72,20 @@ public function build(ExpressionInterface $expression, array &$params = []): str
      * @throws InvalidArgumentException
      * @throws InvalidConfigException
      * @throws NotSupportedException
-     *
-     * @psalm-param ArrayExpression $expression
      */
-    protected function buildPlaceholders(ExpressionInterface $expression, array &$params): array
+    private function buildPlaceholders(ArrayExpression $expression, array &$params): array
     {
         $placeholders = [];
 
         /** @psalm-var mixed $value */
         $value = $expression->getValue();
 
-        if (!is_array($value) && !$value instanceof Traversable) {
+        if (!is_iterable($value)) {
             return $placeholders;
         }
 
         if ($expression->getDimension() > 1) {
-            /** @psalm-var ExpressionInterface|int $item */
+            /** @psalm-var mixed $item */
             foreach ($value as $item) {
                 $placeholders[] = $this->build($this->unnestArrayExpression($expression, $item), $params);
             }
@@ -109,10 +104,9 @@ protected function buildPlaceholders(ExpressionInterface $expression, array &$pa
 
             if ($item instanceof ExpressionInterface) {
                 $placeholders[] = $this->queryBuilder->buildExpression($item, $params);
-                continue;
+            } else {
+                $placeholders[] = $this->queryBuilder->bindParam($item, $params);
             }
-
-            $placeholders[] = $this->queryBuilder->bindParam($item, $params);
         }
 
         return $placeholders;
@@ -126,7 +120,7 @@ private function unnestArrayExpression(ArrayExpression $expression, mixed $value
     /**
      * @return string The typecast expression based on {@see type}.
      */
-    protected function getTypeHint(ArrayExpression $expression): string
+    private function getTypeHint(ArrayExpression $expression): string
     {
         $type = $expression->getType();
 
@@ -135,10 +129,8 @@ protected function getTypeHint(ArrayExpression $expression): string
         }
 
         $dimension = $expression->getDimension();
-        $result = '::' . $type;
-        $result .= str_repeat('[]', $dimension);
 
-        return $result;
+        return '::' . $type . str_repeat('[]', $dimension);
     }
 
     /**
@@ -149,7 +141,7 @@ protected function getTypeHint(ArrayExpression $expression): string
      *
      * @return string The sub-query array expression.
      */
-    protected function buildSubqueryArray(string $sql, ArrayExpression $expression): string
+    private function buildSubqueryArray(string $sql, ArrayExpression $expression): string
     {
         return 'ARRAY(' . $sql . ')' . $this->getTypeHint($expression);
     }
@@ -157,7 +149,7 @@ protected function buildSubqueryArray(string $sql, ArrayExpression $expression):
     /**
      * @return array|bool|ExpressionInterface|float|int|JsonExpression|string|null The cast value or expression.
      */
-    protected function typecastValue(
+    private function typecastValue(
         ArrayExpression $expression,
         array|bool|float|int|string|ExpressionInterface|null $value
     ): array|bool|float|int|string|JsonExpression|ExpressionInterface|null {
diff --git a/src/Builder/JsonExpressionBuilder.php b/src/Builder/JsonExpressionBuilder.php
index f8562eebb..e86fda354 100644
--- a/src/Builder/JsonExpressionBuilder.php
+++ b/src/Builder/JsonExpressionBuilder.php
@@ -29,7 +29,7 @@ public function __construct(private QueryBuilderInterface $queryBuilder)
     /**
      * The Method builds the raw SQL from the $expression that won't be additionally escaped or quoted.
      *
-     * @param ExpressionInterface $expression The expression to build.
+     * @param JsonExpression $expression The expression to build.
      * @param array $params The binding parameters.
      *
      * @throws Exception
@@ -39,19 +39,15 @@ public function __construct(private QueryBuilderInterface $queryBuilder)
      * @throws NotSupportedException
      *
      * @return string The raw SQL that won't be additionally escaped or quoted.
-     *
-     * @psalm-param JsonExpression $expression
      */
     public function build(ExpressionInterface $expression, array &$params = []): string
     {
-        /**
-         * @psalm-var array|mixed|QueryInterface $value
-         */
+        /** @psalm-var mixed $value */
         $value = $expression->getValue();
 
         if ($value instanceof QueryInterface) {
             [$sql, $params] = $this->queryBuilder->build($value, $params);
-            return "($sql)" . $this->getTypecast($expression);
+            return "($sql)" . $this->getTypeHint($expression);
         }
 
         if ($value instanceof ArrayExpression) {
@@ -60,13 +56,13 @@ public function build(ExpressionInterface $expression, array &$params = []): str
             $placeholder = $this->queryBuilder->bindParam(Json::encode($value), $params);
         }
 
-        return $placeholder . $this->getTypecast($expression);
+        return $placeholder . $this->getTypeHint($expression);
     }
 
     /**
      * @return string The typecast expression based on {@see JsonExpression::getType()}.
      */
-    protected function getTypecast(JsonExpression $expression): string
+    private function getTypeHint(JsonExpression $expression): string
     {
         $type = $expression->getType();
 
diff --git a/src/ColumnSchema.php b/src/ColumnSchema.php
index a40a6ab78..db39d788b 100644
--- a/src/ColumnSchema.php
+++ b/src/ColumnSchema.php
@@ -65,8 +65,7 @@ final class ColumnSchema extends AbstractColumnSchema
      *
      * @param mixed $value input value
      *
-     * @return mixed Converted value. This may also be an array containing the value as the first element and the PDO
-     * type as the second element.
+     * @return mixed Converted value.
      */
     public function dbTypecast(mixed $value): mixed
     {
@@ -87,7 +86,7 @@ public function dbTypecast(mixed $value): mixed
 
             Schema::TYPE_BIT => is_int($value)
                 ? str_pad(decbin($value), (int) $this->getSize(), '0', STR_PAD_LEFT)
-                : $this->typecast($value),
+                : (string) $value,
 
             default => $this->typecast($value),
         };
@@ -111,15 +110,15 @@ public function phpTypecast(mixed $value): mixed
                 $value = $this->getArrayParser()->parse($value);
             }
 
-            if (is_array($value)) {
-                array_walk_recursive($value, function (string|null &$val) {
-                    /** @psalm-var mixed $val */
-                    $val = $this->phpTypecastValue($val);
-                });
-            } else {
+            if (!is_array($value)) {
                 return null;
             }
 
+            array_walk_recursive($value, function (mixed &$val) {
+                /** @psalm-var mixed $val */
+                $val = $this->phpTypecastValue($val);
+            });
+
             return $value;
         }
 
@@ -131,7 +130,7 @@ public function phpTypecast(mixed $value): mixed
      *
      * @throws JsonException
      */
-    protected function phpTypecastValue(mixed $value): mixed
+    private function phpTypecastValue(mixed $value): mixed
     {
         if ($value === null) {
             return null;
@@ -152,7 +151,7 @@ protected function phpTypecastValue(mixed $value): mixed
     /**
      * Creates instance of ArrayParser.
      */
-    protected function getArrayParser(): ArrayParser
+    private function getArrayParser(): ArrayParser
     {
         return new ArrayParser();
     }
diff --git a/tests/ColumnSchemaTest.php b/tests/ColumnSchemaTest.php
index 01b8ed031..2c8195acb 100644
--- a/tests/ColumnSchemaTest.php
+++ b/tests/ColumnSchemaTest.php
@@ -188,4 +188,13 @@ public function testNegativeDefaultValues()
         $this->assertSame(-12345.6789, $tableSchema->getColumn('float_col')->getDefaultValue());
         $this->assertSame(-33.22, $tableSchema->getColumn('numeric_col')->getDefaultValue());
     }
+
+    public function testDbTypeCastBit()
+    {
+        $db = $this->getConnection(true);
+        $schema = $db->getSchema();
+        $tableSchema = $schema->getTableSchema('type');
+
+        $this->assertSame('01100100', $tableSchema->getColumn('bit_col')->dbTypecast('01100100'));
+    }
 }
diff --git a/tests/QueryBuilderTest.php b/tests/QueryBuilderTest.php
index b57378150..39e6ba959 100644
--- a/tests/QueryBuilderTest.php
+++ b/tests/QueryBuilderTest.php
@@ -204,6 +204,17 @@ public function testAlterColumn(): void
             ),
         );
 
+        $this->assertSame(
+            <<<SQL
+            ALTER TABLE "foo1" ALTER COLUMN "bar" TYPE varchar(30), ADD UNIQUE ("bar")
+            SQL,
+            $qb->alterColumn(
+                'foo1',
+                'bar',
+                (new Column(SchemaInterface::TYPE_STRING, 30))->unique()
+            ),
+        );
+
         $db->close();
     }