[2.1] Proposal for handling primary keys in migrations.

[Faryshta]

Currently the class yii\db\Migration has a methods primaryKey() and bigPrimaryKey() which create a column based on Schema::TYPE_PK or Schema::TYPE_BIGPK respectively.

I propose to move the primaryKey() method to the yii\db\ColumnSchemaBuilder class as a column modifier with the signature.

/**
 * @var boolean|null $autoIncrement if this column use AUTO_INCREMENT.
 * this variable is null then the value will be determined on whether or not this
 * column is integer or big interger.
 * @return $this the column schema builder itself
 */
public function primaryKey($autoIncrement = null);

Usage

public function up()
{
    $this->createTable('post', [
          'id' => $this->integer()->primaryKey(), // automatically sets AUTO_INCREMENT
          //...
    ]);

    $this->createTable('tag', [
          'tag' => $this->string()->primaryKey(), // doesn't set AUTO_INCREMENT
          //...
    ]);
}

And for mixed primary keys I propose to create a new method. yii\db\Migration::tablePrimaryKey() (the name can be different) with signature.

/**
 * @var string[] $columns the columns to be used.
 * @return string
 */
public function tablePrimary(...$columns):

Usage

public function up()
{
    $this->createTable('post', [
          'id' => $this->integer()->primaryKey(),
          //...
    ]);

    $this->createTable('tag', [
          'tag' => $this->string()->primaryKey(),
          //...
    ]);

    $this->createTable('post_tag', [
          'post_id' => $this->integer()->foreignKey(),
          'tag' => $this->string()->foreignKey(),

          $this->tablePrimaryKey('post_id', 'tag');
    ])
}

the ...$column syntax is available since php5.6 but we can use simple arrays instead. If you don't like the method name tablePrimaryKey() please propose something else in comments.

[samdark]

Yes. Good idea.

[mdmunir]

No break BC if only add primaryKey() method.

[Faryshta]

@samdark how about we folow the advice of @mdmunir ? and make Migration::primaryKey() a shortcut for Migration::integer()->primaryKey() ?

The Schema::TYPE_PK and similar constants wouldn't be useful anymore so I deleted them already on the branch where I am working for this PR.

[Faryshta]

I prepared two PR's. One for 2.0 with bc compatibility as suggested by @mdmunir and one for 2.1 with BC Break.

[Tigrov]

Duplicate of #6 and #7