On Tuesday, 19 July 2022 at 17:05:27 UTC, Kagamin wrote:
Also what's the difference between null and empty phone number?
In a relational database, `NULL` is not the same that `""`... and
`NULL` is not the same that `0`. Are semantically different and
there are database invariants (like foreign keys) based on it.
Trying to "mix" this concepts in a database is a mistake.
When you treat with Domain Models, you try to represent this
semantics in all levels of your software... including APIs
If your address has not a reference to the city... then there is
a `city_code` field with `NULL` value in your database and the
Address model object has a city property representing this Null
value with the tools that language/library offers to you:
`Nullable!City` or `Sumtype!(Null, City)` or `Optional<City>` or
...).
`Null` is then a valid value state that has nothing related to
*`null` pointers*... to avoid confusion, I talk about `Null`
instead `null`.
I, personally, prefer to use Union types (algebraic types) like
`int | Null | ...` because it is the best option to introduce the
Undefined state (that allows statically typed data to represent
the absence of a property).
`Sumtype!(Undefined,Null,int)` instead `Optional!(Nullable!int)`
Then there is the `match!` syntax, the unified way to treat JSON
serialization and the easy way to implement a custom "dot"
accessor that propagates the Null or Undefined state in a chain
of references:
```d
person.ns.address.ns.city.ns.name.match!(
(string name){ ... }
(Null) {...}
(Undefined) { ... }
)
```
