Merge pull request #9518 from pana1990/patch

Fix code style and delete declaration of yii\db\Schema [skip ci]

docs/guide/db-migrations.md

@@ -65,20 +65,32 @@ a migration class `m150101_185401_create_news_table` with the skeleton code:
 ```php
 <?php
 
-use yii\db\Schema;
 use yii\db\Migration;
 
 class m150101_185401_create_news_table extends Migration
 {
     public function up()
     {
+
     }
 
     public function down()
     {
         echo "m101129_185401_create_news_table cannot be reverted.\n";
+
         return false;
     }
+
+    /*
+    // Use safeUp/safeDown to run migration code within a transaction
+    public function safeUp()
+    {
+    }
+
+    public function safeDown()
+    {
+    }
+    */
 }
 ```
 
@@ -114,7 +126,6 @@ class m150101_185401_create_news_table extends Migration
     {
         $this->dropTable('news');
     }
-
 }
 ```
 
@@ -147,7 +158,6 @@ could be written like the following:
 ```php
 <?php
 
-use yii\db\Schema;
 use yii\db\Migration;
 
 class m150101_185401_create_news_table extends Migration
@@ -165,7 +175,6 @@ class m150101_185401_create_news_table extends Migration
     {
         $this->dropTable('news');
     }
-
 }
 ```
 
@@ -185,8 +194,8 @@ As a result, if any operation in these methods fails, all prior operations will
 In the following example, besides creating the `news` table we also insert an initial row into this table.
 
 ```php
+<?php
 
-use yii\db\Schema;
 use yii\db\Migration;
 
 class m150101_185401_create_news_table extends Migration
@@ -449,7 +458,8 @@ database. To achieve this goal, when implementing a migration class you should e
 ID that the migration would use, like the following:
 
 ```php
-use yii\db\Schema;
+<?php
+
 use yii\db\Migration;
 
 class m150101_185401_create_news_table extends Migration