Question

我是Laravel的新手并且有这样的迁移：

public function up()
{
    Schema::table('mytable', function(Blueprint $table)
    {
        $table->renameColumn('mycol', 'old_mycol');
        $table->string('mycol', 100);
    });
}

当我运行它时，我收到错误：

[PDOException]
SQLSTATE [42S21]：列已存在：1060重复的列名＆＃39; mycol＆＃39;

我最终把它分成了两个单独的迁移，并且工作正常，但我不明白为什么一次性完成它是一个问题。

Answer 1

这是因为Laravel会在执行迁移时隐式地在命令数组的最开头添加任何添加新列或修改现有列的命令。以下代码直接取自Illuminate\Database\Schema\Blueprint类。

/**
 * Get the raw SQL statements for the blueprint.
 *
 * @param  \Illuminate\Database\Connection  $connection
 * @param  \Illuminate\Database\Schema\Grammars\Grammar  $grammar
 * @return array
 */
public function toSql(Connection $connection, Grammar $grammar)
{
    $this->addImpliedCommands();

    $statements = array();

    // Each type of command has a corresponding compiler function on the schema
    // grammar which is used to build the necessary SQL statements to build
    // the blueprint element, so we'll just call that compilers function.
    foreach ($this->commands as $command)
    {
        $method = 'compile'.ucfirst($command->name);

        if (method_exists($grammar, $method))
        {
            if ( ! is_null($sql = $grammar->$method($this, $command, $connection)))
            {
                $statements = array_merge($statements, (array) $sql);
            }
        }
    }

    return $statements;
}

/**
 * Add the commands that are implied by the blueprint.
 *
 * @return void
 */
protected function addImpliedCommands()
{
    if (count($this->getAddedColumns()) > 0 && ! $this->creating())
    {
        array_unshift($this->commands, $this->createCommand('add'));
    }

    if (count($this->getChangedColumns()) > 0 && ! $this->creating())
    {
        array_unshift($this->commands, $this->createCommand('change'));
    }

    $this->addFluentIndexes();
}

从上面的代码中可以看出，在toSql方法中，调用addImpliedCommands，其中可能会将几个命令添加到对象的命令数组的开头。这会导致在重命名命令之前首先执行新mycol列的命令。

要解决此问题，不确实需要创建两个迁移。在同一次迁移中，您只需简单地调用Schema::table()两次：

Schema::table('mytable', function(Blueprint $table)
{
    $table->renameColumn('mycol', 'old_mycol');
});

Schema::table('mytable', function(Blueprint $table)
{
    $table->string('mycol', 100);
});

Laravel 5迁移：重命名列时出错

1 个答案: