src/Database/Schema/SqliteSchema.php
public function addForeignKey($name, $table, $columns, $refTable, $refColumns, $delete = null, $update = null)
    {
        throw new \Exception('Adding a foreign key constraint to an existing table is not supported by SQLite.');
    }
public function addForeignKey($name, $table, $columns, $refTable, $refColumns, $delete = null, $update = null)
    {
        throw new \Exception('Adding a foreign key constraint to an existing table is not supported by SQLite.');
    }
public function addForeignKey ( $ name , $ table , $ columns , $ refTable , $ refColumns , $ delete = null , $ update = null ) { throw new \ Exception ( 'Adding a foreign key constraint to an existing table is not supported by SQLite.' ) ; }
Builds a SQL statement for adding a foreign key constraint to an existing table.
Because SQLite does not support adding foreign key to an existing table, calling this method will throw an
exception.

@param string $name       the name of the foreign key constraint.
@param string $table      the table that the foreign key constraint will be added to.
@param string $columns    the name of the column to that the constraint will be added on. If there are multiple
columns, separate them with commas.
@param string $refTable   the table that the foreign key references to.
@param string $refColumns the name of the column that the foreign key references to. If there are multiple
columns, separate them with commas.
@param string $delete     the ON DELETE option. Most DBMS support these options: RESTRICT, CASCADE, NO ACTION,
SET DEFAULT, SET NULL
@param string $update     the ON UPDATE option. Most DBMS support these options: RESTRICT, CASCADE, NO ACTION,
SET DEFAULT, SET NULL

@throws \Exception
@return string the SQL statement for adding a foreign key constraint to an existing table.
Builds a SQL statement for adding a foreign key constraint to an existing table . Because SQLite does not support adding foreign key to an existing table calling this method will throw an exception .