Question

I have a problem and I just do not know how to solve it.
I want to model in JAVA a structure like: Companies, Events and Locations.

• Each Company includes one or many Location/s which represents the places where a branch of the company is
• Each event also has a Location where the event takes place

Here’s the code:

public class Event {
    int id;
    String name;
    Location location;
    ...
}

public class Location {
    int id;
    String name;
    String building;
    ...
}

public class Company {
    int id;
    String name;
    Collection<Location> locations;
    ...
}

My problem is that i want to use ORMLite for saving the objects in a Database. But if I understood the foreign things in ORMLite correctly, i have to add a Company instance variable to the Location:

public class Location {
  @DatabaseField(columnName = "com_id", foreign = true)
  Company company;
  @DatabaseField(id = true, columnName = "loc_id")
  int id;
  @DatabaseField(columnName = "loc_name")
  String name;
  @DatabaseField(columnName = "loc_build")
  String building;
  ...
}

public class Company {
  @DatabaseField(columnName = "com_id")
  int id;
  @DatabaseField(columnName = "com_name")
  String name;
  @ForeignCollectionField()
  Collection<Location> locations;
  ...
}

But now the Location doesn’t work for the Events!?! How can I implement such a behaviour?

Thank you for your answers

Answer 1

Somehow you need to assign “ownership” of a Location by a Company. You can do this in (at least) 2 different ways.

1. As you mentioned, you can have a Location has a Company field. This would work fine if there was a one-to-one relationship there. It would not work if you are trying to have one "Pittsburgh" Location and you want both "Alcoa" and "US Steel" companies having a location in Pittsburgh.

2. The 2nd way to implement it is to have a CompanyLocation entity which is often called a join-table in ORM languages. ORMLite does not make this join table for you however.

   public class CompanyLocation {
      @DatabaseField(foreign = true)
      Company company;
      @DatabaseField(foreign = true)
      Location location;
   }
   

   So if want "Alcoa" to have a Location of "Pittsburgh" you need to insert a CompanyLocation into the table which defines the relationship.

Hope this helps.