I have a 3 tables with the current relationships

Event
Project
Task

Event to Project is 1:1 Uni Directional currently
Project to Task is 1:Many Uni Directional currently

I have realised that because I want to "navigate" up the relationship from task back to Event I need to make the relationships Bi-Directional.

Is there any reason I shouldn't use a join table (as opposed to recording the foreign keys on each respective table?

Second question:

I think I will need to change Event -> Project from 1:1 to Many:1, but if I want to retain the ability to navigate up the relationship from task to Event - which event should the system "choose" as it will have many to pick from?

I would like to use the most recent Event to de displayed to use, so I assume the best way to do this is to put a creationDate on event and then the system can choose the newest?

THoughts?

Thanks

-AL

Join tables are suitable for many-to-many associations, not for one-to-many associations which only require a single FK on the client-side. Check out this article for more details.

[url]I would like to use the most recent Event to de displayed to use, so I assume the best way to do this is to put a creationDate on event and then the system can choose the newest?[/url]

You can even map the latest child of a one-to-many association using @JoinFormula. Check out this article for more details.

So if I understand that article correctly, reading the last heading in the article "Just @ManyToOne" then :

Many (Event) to One (Project) is best done by @ManyToOne on the child side. How do you determine which is the child? (I'm guessing it has to be the many (Event)).

Then the article goes on to say in order to make it bidrectional and be able to get the Project associated with a given Event you need to setup a JPQL query to get the Project?

Just want to check I am on the right track....

Cheers

Al

It's very easy to determine which one is the child side in a one-to-one or one-to-many association. If you look at the database tables, the table that has the FK (e.g. Event) and cannot live without its parent (e.g. Project) is a child.

So, can you have an Event without a Parent? Well, even if you can, can you have multiple Projects assigned to an Event or multiple Events assigned to a Project? The many side distates the child side, hence the placement of the FK.



Nope. Bidirectional means that you can navigate the association both ways. However, you can also use a JPQL query for the parent side. It's not like you always have to use bidirectional associations.

So how then would you make it bi-directional? With the FK on event, if you have a project how do you determine which events are related to it?

This article explains how to map a one-to-one association and why making it bidirectional is not very useful.

But we are talking about ManyToOne - not OneToOne.

According to your initial description, there is a 1:1 association between Event and Project

Hi Vlad

Yes but first sentence after second question I state I will have to change it to Many:1

Shoudl end up as:

Event(Few)---Project(1)----Tasks(Few)

And be fully bidirectional.

Cheers

Al