Given the schema:

What I need is having every user_identities.belongs_to reference an users.id.

At the same time, every users has a primary_identity as shown in the picture.

However when I try to add this reference with ON DELETE NO ACTION ON UPDATE NO ACTION, MySQL says

#1452 - Cannot add or update a child row: a foreign key constraint fails (yap.#sql-a3b_1bf, CONSTRAINT #sql-a3b_1bf_ibfk_1 FOREIGN KEY (belongs_to) REFERENCES users (id) ON DELETE NO ACTION ON UPDATE NO ACTION)

I suspect this is due to the circular dependency, but how could I solve it (and maintain referential integrity)?