On Tuesday, 19 July 2022 at 08:10:25 UTC, Kagamin wrote:
On Monday, 18 July 2022 at 21:23:32 UTC, Antonio wrote:
I will study it in detail and report (if required). May be, I
will write the DTO problem with D article if I find time in
august.
In my experience null and empty in DTOs usually play the same
logical role. It's a very contrived technical difference
without practical usage, such distinction is way beyond any
business logic. Even if you implement this distinction, I'm not
sure anybody will carefully pay attention to it. In languages
that make difference between null and empty, null is often
replaced with empty to work around problems with null, such
codebase can't properly preserve null values.
When you have to "patch" information partially (i.e.: update only
the name and the phonenumber, but not the birthdate) or you must
return in a REST partial information (because graphql or custom
REST) there is only 2 ways to represent this "possible missing
properties"
* Maps (key->value) or similiar (i.e.:JSon objects): You can
include or not keys in the map: If you don't want to update the
birthdate, don't include the birthdate key in the DTO.
* Structs (or any kind of structured data that can be validated
at compile time): There is no possibility to say that some
properties of the struct can be not present... Well, you can if
you begin to manage Algebraic Types (Union types): `height:
int | undefined`
NULL is not the same that UNDEFINED
The distintion is really important: NULL is a valid value (i.e.:
The person phonenumber is NULL in database)... Of course, you can
represent this concept natively in you language (Nullable,
Optional, Maybe ...) but it is not the same that UNDEFINED...
because UNDFINED says "This property has not been assigned to
DTO... do not take it into account".
The summary is that a DTO that works like a Map needs to
represent the absent key ant this is not the same that the Null
value
Example:
```d
struct Null { /*...*/ }
struct Undefined { /*...*/ }
struct ContactDto {
DtoVal!(Undefined, string) name
DtoVal!(Undefined, Null, string) phonenumber,
DtoVal!(Undefined, AddressDto) address
}
// ...
ContactDto data = {phonenumber:Null(),
address:{city:{code:"BCN"}}};
updateContact(id, data);
```
