add comment function for MySQL ColumnSchemaBuilder in yii2 2.0.7

ColumnSchemaBuilder.php

<?php

namespace common\components;

class ColumnSchemaBuilder extends \yii\db\ColumnSchemaBuilder
{
    protected $comment;

    /**
     * @inheritdoc
     */
    public function __toString()
    {
        return
            $this->type .
            $this->buildLengthString() .
            $this->buildUnsignedString() .
            $this->buildNotNullString() .
            $this->buildUniqueString() .
            $this->buildDefaultString() .
            $this->buildCheckString() .
            $this->buildCommentString();
    }

    public function buildCommentString()
    {
        return $this->comment ? " COMMENT '{$this->comment}'" : '';
    }

    public function comment($comment)
    {
        $this->comment = $comment;

        return $this;
    }
}

main.php

<?php

return [
    'components' => [
        'db' => [
            // ... ... 
            // add these three lines
            'schemaMap' => [
                'mysql' => 'common\components\MysqlSchema',
            ],
        ],
    ],
];

MysqlSchema.php

<?php

namespace common\components;

use yii\db\mysql\Schema;

class MysqlSchema extends Schema
{
    /**
     * @inheritdoc
     */
    public function createColumnSchemaBuilder($type, $length = null)
    {
        return new ColumnSchemaBuilder($type, $length);
    }
}