Question

i am actually reading Doctrine Reference: One to Many, Unidirectional with Join table. but this will probably be more of a SQL quesiton. basically, this is supposed to model a one to many, unidirectional relationship. i guess from the PHP code (in that link), its such that 1 user have many phonenumbers.

the question is from the SQL, it seems like 1 user can have many phonenumbers. and 1 phonenumber can only belong to 1 user. am i right?

CREATE TABLE User (
    id INT AUTO_INCREMENT NOT NULL,
    PRIMARY KEY(id)
) ENGINE = InnoDB;

CREATE TABLE users_phonenumbers (
    user_id INT NOT NULL,
    phonenumber_id INT NOT NULL,
    UNIQUE INDEX users_phonenumbers_phonenumber_id_uniq (phonenumber_id),
    PRIMARY KEY(user_id, 
phonenumber_id)
) ENGINE = InnoDB;

CREATE TABLE Phonenumber (
    id INT AUTO_INCREMENT NOT NULL,
    PRIMARY KEY(id)
) ENGINE = InnoDB;

ALTER TABLE users_phonenumbers ADD FOREIGN KEY (user_id) REFERENCES User(id);
ALTER TABLE users_phonenumbers ADD FOREIGN KEY (phonenumber_id) REFERENCES Phonenumber(id);

can’t i just simplify the database to … below … no need for join tables and what not?

Users (id, name)
Phonenumbers (id, user [FK], number)

Answer 1

Correct, these are two valid approaches to the same problem. And yes, the unique index on users_phonenumbers means that each phone number can belong to only one user.