DDL Generation support for foreign key cascade options

[rbygrave]

Provide annotations / ddl generation to support generating foreign key cascade options such as delete cascade.

[rbygrave]

JPA Does not yet provide standard annotations for this, we note that Hibernate and Eclipselink have there own annotations to support this - @OnDelete and @CascadeOnDelete.

I am not convinced by either of the Hibernate or Eclipselink annotations and the current proposal is to instead have:

A new annotation @DbForeignKey with options for

• onDelete ... to control the on delete clause ( cascade, set null, set default, restrict)
• onUpdate... to control the on update clause ( cascade, set null, set default, restrict)
• noConstraint ... true | false ... set to true to have no constraint at all
• noIndex ... true | false ... set to true to have no index created

Examples:

@ManyToOne
@DbForeignKey(onDelete=ConstraintMode.CASCADE)

@ManyToOne
@DbForeignKey(onDelete=ConstraintMode.SET_NULL)

// no constraint but still have an index created
@ManyToOne
@DbForeignKey(noConstraint=true)

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Note that with the onDelete modes of CASCADE, SET_NULL, SET_DEFAULT Ebean is not performing those updates/deletes (the DB is) and hence Ebean is not maintaining the L2 cache if it is being used on the related entity types.

That is, there will be some events that are no longer sent as we do not longer know or in theory care what is set via the DB handling the cascade etc. These options should be used with these known limitations on the event notification and L2 cache.