Oracle if value to be inserted in foreign key is -1, insert null instead

Question

I have a xml script I'm reading from to populate my database with data. One of the nodes in the xml file don't have a idDirector field (the nodes are movies) and so the xml reads a -1 as idDirector and then my stored procedure tries to insert -1 into the fk field and this makes my database returna constraint error : director -1 doesn't exist in Director table. How can I make it so it inserts null instead and make my fk field nullable?

CREATE TABLE Film (
    PRIMARY KEY (idFilm),
    FOREIGN KEY (idDirector) REFERENCES Director
);

Thank you

Answer 1

Looks like CASE to me, e.g.

insert into film (id_film, id_director)
select id_film,
       case when id_director = -1 then null
            else id_director
       end
from ...

---

Will it work? Yes:

SQL> create table director (id number primary key);

Table created.

SQL> create table film (id number primary key, id_director number references director);

Table created.

SQL> insert into director values (100);

1 row created.

Inserting -1 fails:

SQL> insert into film (id, id_director) values (1, -1);
insert into film (id, id_director) values (1, -1)
*
ERROR at line 1:
ORA-02291: integrity constraint (SCOTT.SYS_C0065885) violated - parent key not
found

Inserting NULL works:

SQL> insert into film (id, id_director) values (1, null);

1 row created.

SQL>