Different inheritance types in the same schema

Question

I'm using Doctrine 1.2 on a symfony project, and I'm considering mixing concrete and column aggregation inheritance types in my schema: column aggregation lets me query in a parent table and get both parent and child records, while concrete inheritance lets me get a cleaner schema. Plus, the mix will be in the same inheritance chain. How would I write the schema file? Like the following?

A:

B:
  inheritance:
    extends: A
    type: concrete

C:
  inheritance:
    extends: B
    type: column_aggregation
    keyField:         type
    keyValue:         1

Or like this perhaps:

A:

B:
  inheritance:
    extends: A
    type: concrete

C:
  inheritance:
    extends: B
    type: concrete
D:
  inheritance:
    extends: C
    type: column_aggregation
    keyField:         type
    keyValue:         1


E:
  inheritance:
    extends: C
    type: column_aggregation
    keyField:         type
    keyValue:         2

Are there any dangers/caveats ?

Answer 1

As long as you avoid circular inheritance or diamond shaped inheritance you would be fine and can use this

A circular inheritance (obviously looks as follows

Class A Extends B Class B Extends A

OR

CLASS A EXTENDS C

CLASS B EXTENDS A

CLASS C EXTENDS A

A Diamond Shaped inheritance is a bit more round about. It happens when the following type of condition happens

CLASS A

CLASS B EXTENDS A

CLASS C EXTENDS A

CLASS D EXTENDS B,C