Documentation issue: Custom row classes about drift

[elkSal]

Thanks a lot, marking as closed then :)
Have a great year in advance and thanks a lot for your library!

[simolus3]

If the phone numbers are stored in the users table, for instance by encoding them as a JSON array of strings, you can combine custom row classes with type converters to get what you're looking for:

import 'package:drift/drift.dart';

@UseRowClass(User)
class Users extends Table {
  IntColumn get id => integer().autoIncrement()();
  TextColumn get email => text()();
  TextColumn get phoneNumbers =>
      text().map(TypeConverter.json(fromJson: (data) {
        return <PhoneNumber>[
          for (final value in data) PhoneNumber.parse(value)
        ];
      }))();
}

class User {
  int id;
  String email;
  List<PhoneNumber> phoneNumbers;

  User({required this.id, required this.email, required this.phoneNumbers});
}

class PhoneNumber {
  Country country;
  String phoneNumber;

  PhoneNumber({required this.country, required this.phoneNumber});

  static PhoneNumber parse(String text) {
    throw UnimplementedError();
  }
}

class Country {
  String name;
  String localeName;
  String phonePrefix;

  Country(
      {required this.name,
      required this.localeName,
      required this.phonePrefix});
}

[elkSal]

thanks a lot as usual for the quick feedback.

What I had in mind was if whether it was possible to link nested row classes. For instance, in the above example, there would be also a RowClass for PhoneNumber and one for Country as they have some additional relationships with other tables that don't allow to use a type converter.
Given that each user can have multiple phone numbers and each number has one country, it was an example to see how would you implement nested row classes with one to many and one to one relationships.

PS:
It would be interesting to see also how would you implement inheritance in row classes.
Let's say we are collecting animal data, we have an class Pet and the various extensions like Dog, Snake, Bird.
Each User (User has a Row Class) can own pets. How would you implement it?

class User {
String email;
Pet pet;
User({required this.email. required this.pet)};
}

class Pet {
int id;
String name;
Pet({required this.id, required this.name});
}

class Dog {
int id;
String race;
Sex sex;
....
}

class Snake{
int id;
bool isVenoumous;
...
}

So far I did it in the usual SQL way, which would be to add a parentId Column in the children Table for one to one or one to many relationship and add a link table with the parentId and the childrenId for many to many relationships.
I was curious if with row classes it would be possible to preserve these relationships in another way.

Thanks a lot and have a great weekend.

[simolus3]

Given that each user can have multiple phone numbers and each number has one country, it was an example to see how would you implement nested row classes with one to many and one to one relationships.
I was curious if with row classes it would be possible to preserve these relationships in another way.

This is not possible with cuatom row classes because drift, by design, doesn't hide the relational structure of the database away from you. You can denormalize your schema and store values as arrays where that is appropriate, but one row class will always describe a single row, not the result of a join.

Each User (User has a Row Class) can own pets. How would you implement it?

If pets are stored in a different table, this shouldn't be part of the row class for users. Instead, you write an additiona class storing the user and their pets as separate fields and write a query with joins to resolve them.