Question

Are self-referencing or recursive foreign keys allowed in sqlite? Is there a special syntax to accomplish this? So far I’ve tried the following to no avail: FOREIGN KEY(ParentPrimaryKeyId) REFERENCES ThisTableName(PrimaryKeyId)

For reference, I’m targeting sqlite 3.6.22 in iOS 4.

Answer 1

Yes sqlite supports self-referencing foreign keys, for example:

sqlite> PRAGMA foreign_keys = ON;
sqlite> CREATE TABLE SomeTable (
   ...>     id INTEGER PRIMARY KEY AUTOINCREMENT,
   ...>     parent_id INTEGER, 
   ...>     FOREIGN KEY(parent_id) REFERENCES SomeTable(id));
sqlite> INSERT INTO SomeTable (parent_id) VALUES (234324);
Error: foreign key constraint failed
sqlite> INSERT INTO SomeTable (parent_id) VALUES (NULL);
sqlite> SELECT * FROM SomeTable;
1|
sqlite> INSERT INTO SomeTable (parent_id) VALUES (1);
sqlite> SELECT * FROM SomeTable;
1|
2|1
sqlite>