strange one-to-one relationship

From: Tore Halset (halse..vv.ntnu.no)
Date: Wed Nov 19 2003 - 04:03:34 EST

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    Hello.

    My database has two tables that look like this. One car can have one
    engine and one engine can only be in one car.

    create table car (car_id int primary key, engine_id int);
    create table engine (engine_id int);

    That looks like a one-to-many, but the car.engine_id column has a unique
    index.

    I have defined this as a one-to-one relationship in cayenne modeler, but
    the relation from engine to car does not work. engine.getCar() does return
    one object, but all of the attributes are null.

    When I try to create a new database from cayenne modeler the following
    erromessage are given.

    "Schema Generation Error - Failed statement: ALTER TABLE engine ADD
    FOREIGN KEY (engine_id) REFERENCES car (engine_id) - ERROR: UNIQUE
    constraint matching given keys for referenced table car not found"

    I have worked around the problem by defining the relation from engine to
    car as a one to many relationship.

     - Tore.

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