foreign key on_delete/on_update action

[jayvdb]

Now that we have db constraints on fkey and many due to #158, the next step is to add a cascade setting.

afaik, there are two options.

1. a #[cascade(delete)] type macro
2. Put the cascade setting as a part of the initialiser, such as ForeignKey(<field>, <optional cascade>)

The first seems easier to added in a non-breaking way.
I've not thought more about it than that.

[jayvdb]

sqlite does have "on update" support as well as "on delete" so that should be added to the design of this feature to get the design right the first time, so any breaking changes occur once.

[jayvdb]

sqlite , mysql, postgres all support

• NO ACTION
• RESTRICT
• SET NULL
• SET DEFAULT
• CASCADE
  I am pretty confident that Oracle does also.

Django has the following options for on_delete which they implement in Python, not using database constraints.

• CASCADE
• DO_NOTHING
• PROTECT
• RESTRICT
• SET
• SET_DEFAULT
• SET_NULL