C#•2d ago

✅ Nested Record Inheritance

I'm trying a bit of inheritance shenanigans, the API I'm working with wraps everything in a data object, which usually has two fields that always appear:

public abstract record CharacterActionResult([property: JsonPropertyName("data")] CharacterActionResultData Data);

public abstract record CharacterActionResultData(
    [property: JsonPropertyName("cooldown")] Cooldown Cooldown,
    [property: JsonPropertyName("character")] Character Character
);

public abstract record CharacterActionResult([property: JsonPropertyName("data")] CharacterActionResultData Data);

public abstract record CharacterActionResultData(
    [property: JsonPropertyName("cooldown")] Cooldown Cooldown,
    [property: JsonPropertyName("character")] Character Character
);

This way I can keep a base record for when I need to access cooldown/character in a generic method, but I can still the define the fields that are different:

public record FightResult(FightResultData Data) : CharacterActionResult(Data);

public record FightResultData(
    [property: JsonPropertyName("fight")] Fight Fight,
    Cooldown Cooldown,
    Character Character
) : CharacterActionResultData(Cooldown, Character);

public record FightResult(FightResultData Data) : CharacterActionResult(Data);

public record FightResultData(
    [property: JsonPropertyName("fight")] Fight Fight,
    Cooldown Cooldown,
    Character Character
) : CharacterActionResultData(Cooldown, Character);

However, I get an error:

0>FightResult.cs(6,43): Error CS8866 : Record member 'Artifacts.Model.Characters.CharacterActionResult.Data' must be a readable instance property or field of type 'Artifacts.Model.Characters.FightResultData' to match positional parameter 'Data'.

Am I looking over something?

13 Replies

MODiX•2d ago

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MODiX•2d ago

Lisa

REPL Result: Failure

public abstract record CharacterActionResult(CharacterActionResultData Data);

public abstract record CharacterActionResultData(
    DateTime Cooldown,
    string Character
);

public record FightResult(FightResultData Data) : CharacterActionResult(Data);

public record FightResultData(
    Guid Fight,
    DateTime Cooldown,
    string Character
) : CharacterActionResultData(Cooldown, Character);

public abstract record CharacterActionResult(CharacterActionResultData Data);

public abstract record CharacterActionResultData(
    DateTime Cooldown,
    string Character
);

public record FightResult(FightResultData Data) : CharacterActionResult(Data);

public record FightResultData(
    Guid Fight,
    DateTime Cooldown,
    string Character
) : CharacterActionResultData(Cooldown, Character);

Exception: CompilationErrorException

- Record member 'CharacterActionResult.Data' must be a readable instance property or field of type 'FightResultData' to match positional parameter 'Data'.

- Record member 'CharacterActionResult.Data' must be a readable instance property or field of type 'FightResultData' to match positional parameter 'Data'.

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333fred•2d ago

What do you actually want to have happen here?

LisaOP•2d ago

I mostly just want a contract so I can access Cooldown/Character across the different result types And if that reduces some duplication, that's a bonus

333fred•2d ago

No, as in literally what do you want to happen? What properties? What are their types?

LisaOP•2d ago

public record FightResult(FightResultData Data) : CharacterActionResult(Data);

public record FightResultData(
    [property: JsonPropertyName("fight")] Fight Fight,
    Cooldown Cooldown, // This one
    Character Character // This one
) : CharacterActionResultData(Cooldown, Character);

public record FightResult(FightResultData Data) : CharacterActionResult(Data);

public record FightResultData(
    [property: JsonPropertyName("fight")] Fight Fight,
    Cooldown Cooldown, // This one
    Character Character // This one
) : CharacterActionResultData(Cooldown, Character);

So I can

CharacterActionResult someResult = GetResult<T>();
someResult.Data.Cooldown;
someResult.Data.Character;

CharacterActionResult someResult = GetResult<T>();
someResult.Data.Cooldown;
someResult.Data.Character;

many things•2d ago

records can't do that, either you use a class to being able to declare new/override or you don't use inheritance, i'm afraid

LisaOP•2d ago

:salute2: Throwing it into a class then, Couldn't find that limitation in the documentation so I figured I was missing something Solved by not hard locking on trying to make records work for no reason:

public abstract class ApiResponse<T>(T data)
{
    [property: JsonPropertyName("data")] 
    public T Data { get; } = data;
}

public abstract class CharacterActionResult(Cooldown cooldown, Character character)
{
    [JsonPropertyName("cooldown")]
    public Cooldown Cooldown { get; } = cooldown;

    [JsonPropertyName("character")]
    public Character Character { get; } = character;
}

public class FightResult(Cooldown cooldown, Character character, Fight fight) : CharacterActionResult(cooldown, character)
{
    [JsonPropertyName("fight")] 
    public Fight Fight { get; } = fight;
}

public abstract class ApiResponse<T>(T data)
{
    [property: JsonPropertyName("data")] 
    public T Data { get; } = data;
}

public abstract class CharacterActionResult(Cooldown cooldown, Character character)
{
    [JsonPropertyName("cooldown")]
    public Cooldown Cooldown { get; } = cooldown;

    [JsonPropertyName("character")]
    public Character Character { get; } = character;
}

public class FightResult(Cooldown cooldown, Character character, Fight fight) : CharacterActionResult(cooldown, character)
{
    [JsonPropertyName("fight")] 
    public Fight Fight { get; } = fight;
}

333fred•22h ago

I know you said solved, but I don't think it's actually solved here. Let me ask a different way: write out, in full form, what you wanted Data to be in both of these locations

LisaOP•22h ago

The abstraction should include:

{
  "data": {
    "cooldown": {
      // Some big object
    },
    "character": {
      // Some big object
    }
  }
}

{
  "data": {
    "cooldown": {
      // Some big object
    },
    "character": {
      // Some big object
    }
  }
}

While the inheriting object should be able to add extras, such that the complete object contains:

// EXAMPLE 1
{
  "data": {
    "cooldown": {
      // Some big object
    },
    "character": {
      // Some big object
    },
    "fight": {
      // Some big object
    }
  }
}

// EXAMPLE 2
{
  "data": {
    "cooldown": {
      // Some big object
    },
    "character": {
      // Some big object
    },
    "destination": {
      // Some big object
    }
  }
}

// EXAMPLE 1
{
  "data": {
    "cooldown": {
      // Some big object
    },
    "character": {
      // Some big object
    },
    "fight": {
      // Some big object
    }
  }
}

// EXAMPLE 2
{
  "data": {
    "cooldown": {
      // Some big object
    },
    "character": {
      // Some big object
    },
    "destination": {
      // Some big object
    }
  }
}

333fred•21h ago

So let's re-examine what you originally wrote. In your FightResult, you have a FightResultData, as opposed to a CharacterActionResultData in the base type Which of those is the type you actually want? What do you want to get when you have an instance of a FightResult?

LisaOP•21h ago

When I have a FightResult I actually want FightResultData. When I have a CharacterActionResult I actually want CharacterActionResultData

333fred•21h ago

Ok, so the problem is that properties don't work this way Let me ask another question: why were you using records in the first place?

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✅ Nested Record Inheritance

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