difference between uni-directional and bi-directional relational relationship?

Question

i wonder what these two words mean.

i encountered them in Doctrine's documentation.

but i cant understand what they mean.

Answer 1

This has to do with whether common usage (within the application domain) would attempt to access both sides of the relationship from the other side... Invoices to products would probably be unidirectional, as akthough we often want to know what products are on an invoice, it is unlikely that you would want to know all the invoices tthat contain a given product.

Stores to products on the other hand is b-directional, as we could easily want to accss both all the products at a specific store, or fins all the stores that sell a specific product.

Bi-Directional is not limited to many-to-many relationships, employee to supervisor could easily be bi-drectional, if, in our domain model, an employee object will need to be able to acesss the employee's supoervisor object, and of course, the supervisors object contains a property that lists all his assigned employees.