Question

I’m trying to create table (using migrations) with foreign key like this

public function safeUp()
{
    $this->createTable('tbl_category', array(
        'id'=>'pk',
        'title'=>'string NOT NULL',
        'url'=>'string NOT NULL UNIQUE'
    ));
    $this->addForeignKey('FK_category', 'tbl_product', 'category_id', 'tbl_category', 'id', 'CASCADE', 'NO ACTION');    
}

It perfectly works in MySQL, but now I want to use SQLite and this code gives an error that in SQLite I can’t add foreign key to existing table, so I looked through the definition of createTable method:

public integer createTable(string $table, array $columns, string $options=NULL)

And tried to use $options param to add my foreign key there, but it generates this:

CREATE TABLE 'tbl_category' (
    "id" integer PRIMARY KEY AUTOINCREMENT NOT NULL,
    "title" varchar(255) NOT NULL,
    "url" varchar(255) NOT NULL UNIQUE
)
CONSTRAINT FK_category
FOREIGN KEY tbl_product(category_id)
REFERENCES tbl_category(id)
ON DELETE CASCADE ON UPDATE NO ACTION

Obviously, that “CONSTRAINT…” code should be inside these brackets, but it doesn’t. So how can I create this foreign key?

Answer 1

Explanation

The function createTable is defined in the source code as:

public function createTable($table, $columns, $options=null)
{
    $cols=array();
    foreach($columns as $name=>$type)
    {
        if(is_string($name))
            $cols[]="\t".$this->quoteColumnName($name).' '.$this->getColumnType($type);
        else
            $cols[]="\t".$type;
    }
    $sql="CREATE TABLE ".$this->quoteTableName($table)." (\n".implode(",\n",$cols)."\n)";
    return $options===null ? $sql : $sql.' '.$options;
}

This tells me that all options are for things that would normally go after a Create statement (but before the final semi-colon), like ENGINE or CHARSET in MySQL. The SQLite syntax is just different and doesn’t allow such options.

The addForeignKey function doesn’t work, it’s just not coded:

public function addForeignKey($name, $table, $columns, $refTable, $refColumns, $delete=null, $update=null)
{
    throw new CDbException(Yii::t('yii', 'Adding a foreign key constraint to an existing table is not supported by SQLite.'));
}

And SQLite doesn’t support altering a table to add a foreign key clause.

Solution

Long story short, you should put the foreign key clause in the column definition (in your product table, not your category table):

$this->createTable('tbl_product', array(
    'id'=>'pk',
    'name'=>'string NOT NULL',
    'category_id'=>'integer NOT NULL REFERENCES tbl_category(id)'
));

Addendum

The idea with foreign keys is that the child table should declare it, not the parent table.