How to remove orphans?

BIZ TMS Aurelius
1

Let's assume I have a class A which references a class B. B shall exist only as part of A, but not each A always has a B.



So I create something like this:





[Entity]

[Table('CLASS_A')]

[Id('FId', TIdGenerator.IdentityOrSequence)]

TClassA = class

    private

      [Column('ID', [TColumnProp.Unique, TColumnProp.Required])]

      FId: Integer;

     

      [Association([TAssociationProp.Lazy], CascadeTypeAll)]

      [ForeignJoinColumn('IDA', [TColumnProp.Required])]

      FClassB : Proxy<TClassB>;

     

     [...]



end;





[Entity]

[Table('CLASS_B')]

[Id('FId', TIdGenerator.IdentityOrSequence)]

TClassA = class

    private

      [Column('ID', [TColumnProp.Unique, TColumnProp.Required])]

      FId: Integer;

     

      [Column('IDA')]

      FIdA: Integer;

     

     [...]



end;





When I assign a new B to an A, how do I make sure that the old B - which is now an orphan - gets deleted from the database?

2

There is no such automatic option for that. You must do it manually by removing the orphan B.

Note that with the associaton you are doing, it's A that references B and not the opposite. Have you even tried that code? ForeignJoinColumn attribute doesn't fit here.

What you can duo is create a Many-Value Association from B to A:
      [ManyValuedAssociation([TAssociationProp.Lazy], CascadeTypeAllRemoveOrphan)] 
      [ForeignJoinColumn('IDA', [TColumnProp.Required])] 
      FClassBList : Proxy<TList<TClassB>>; 

This makes more sense, which means B objects (records) reference A objects (records). Thus if you remove a B object from A.FClassBList, they will be removed as well.

3

No, I haven't tried that code.



I actually had this many-to-one association before, but it turned out that I need max. 1 instance of B.



Anyway, I keep it like that but make sure in the property accessors that I have maximum one element in the list.