Adding column with foreign key into table. - postgresql

Question

I have some problem. I want to add new column into my table that references to other column in other table. I do something like that:
class m161202_153033_dodanie_informacji_o_obsludze_prawnej_do_pozyczki extends CDbMigration
{
public function safeUp()
{
$this->execute("ALTER TABLE loan ADD COLUMN administrator int NOT NULL DEFAULT 15 REFERENCES person (id) ON UPDATE CASCADE ON DELETE NO ACTION;");
}
public function safeDown()
{
$this->execute("ALTER TABLE loan DROP COLUMN administrator;");
}
}
But when i try to execute this migration i have this error:
Foreign key violation: 7
DETAIL: Key (administrator)=(15) doesn't appear in table "person"..
I know that there is no suck column "administrator" in my table. But i want to add new column "administrator" into loan table. I wanted to make "administrator" foreign key from person table, column "id". Can u help me, what am i doing wrong?

Answer 1

The error means that there is no row in person with id equal to 15, which would be required for the constraint to be fulfilled.
When you run that ALTER TABLE statement, the table has to be rewritten, and the new column is filled with the value 15.
Often it is easier to create a new column nullable and without default value (then ALTER TABLE will not rewrite the table) and use UPDATE to populate the new column. After that you can change the column definition to NOT NULL and add a default value.

Answer 2

Try this
class m161202_153033_dodanie_informacji_o_obsludze_prawnej_do_pozyczki extends CDbMigration
{
public function safeUp()
{
$this->execute("INSERT INTO person (id) VALUES (15) ON CONFLICT (id) DO NOTHING;");
$this->execute("ALTER TABLE loan ADD COLUMN administrator int NOT NULL DEFAULT 15 REFERENCES person (id) ON UPDATE CASCADE ON DELETE NO ACTION;");
}
public function safeDown()
{
$this->execute("ALTER TABLE loan DROP COLUMN administrator;");
}
}