cds 9: modified input validations

[David-Kunz]

• rm @readonly and @insertonly from Access Control Annotations
• rm @Common.FieldControl from Input Validation
• rm @assert.notNull from Input Validation
• mv @assert.unique to Database Constraints
• add link to database constraints in Input Validations
• document not null in Database Constraints
• document not null (in actions/functions)

[agoerler]

I am afraid that we have not sufficiently discussed the meaning of not null for calculated/computed elements.

[agoerler]

Should we mention that key elements are implicitly not null?

If an element is defined in a view as not null this is not enforced by the DB, I think. Same applies to calculated elements on write.

Moreover not null is a guarantee that the element is never null.

[David-Kunz]

If an element is defined in a view as not null

How does one achieve this? Is that even possible?

[agoerler]

I checked and have the impression that it's not possible.

But then, the question arises: How do I express that a virtual/calculated/@CoreComputed element is guaranteed to not be null?

[agoerler]

I have double-checked with @stewsk - you can actually define a virtual element, which is not null:

type NotNullableString : String not null;

view V as select from E { *, 'x' as nns : NotNullableString };

this is not possible, however:

view V as select from E { *, 'x' as nns : String not null };

[danjoa]

• did some more cleanup in e66a912
• see the check marks in the top comment
• Fine for me with that.

[danjoa]

@renejeglinsky ready to merge