Make TaskCache Observable by Dataloaders

[PascalSenn]

Enables dataloaders to observe the cache. This makes it possible that DataLoaders can build their state based on the result of other dataloaders

An example

public record Person(Guid Id, string Username);

public class PersonByIdDataLoader : BatchDataLoader<Guid, Person?> 
{
    // left out for brevity

    protected override ValueTask FetchAsync(
        IReadOnlyList<TKey> keys,
        Memory<Result<TValue>> results,
        CancellationToken cancellationToken)
        => _service.GetByIds(keys, results, cancellationToken);
    }
}

public class PersonByUserNameDataLoader : BatchDataLoader<string, Person?> 
{
    // left out for brevity

    protected override ValueTask FetchAsync(
        IReadOnlyList<TKey> keys,
        Memory<Result<TValue>> results,
        CancellationToken cancellationToken)
        => _service.GetByUserName(keys, results, cancellationToken);
    }
}

If these two dataloaders are used in the same query, it could be that both dataloaders load the same value from the database. Only one fetch would have been enough though, as the PersonByIdDataLoader could inform the other Dataloader about the fetched person.

In the following example, the data is only fetched once.

public record Person(Guid Id, string Username);

public class PersonByIdDataLoader : BatchDataLoader<Guid, Person?>, ITaskCacheObserver 
{
    // left out for brevity

    protected override ValueTask FetchAsync(
        IReadOnlyList<TKey> keys,
        Memory<Result<TValue>> results,
        CancellationToken cancellationToken)
        => _service.GetByIds(keys, results, cancellationToken);
    }

    public bool CanHandle(object value) => value is Person;

    public void OnNext(object value)
    {
        if(value is Person p) 
        {
            Set(p.Id, p);
        }
    }
}

public class PersonByUserNameDataLoader : BatchDataLoader<string, Person?>, ITaskCacheObserver 
{
    // left out for brevity

    protected override ValueTask FetchAsync(
        IReadOnlyList<TKey> keys,
        Memory<Result<TValue>> results,
        CancellationToken cancellationToken)
        => _service.GetByUserName(keys, results, cancellationToken);
    }
    
    public bool CanHandle(object value) => value is Person;

    public void OnNext(object value)
    {
        if(value is Person p) 
        {
            Set(p.UserName, p);
        }
    }
}

[michaelstaib]

@PascalSenn was this one for 13 or 12.x?

[PascalSenn]

i guess 13 as its a breaking one? not sure

[sonarqubecloud[bot]]

SonarCloud Quality Gate failed.   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
6 Code Smells

29.4% Coverage
0.0% Duplication

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Codecov Report

Attention: Patch coverage is 87.50000% with 7 lines in your changes missing coverage. Please review.

Project coverage is 76.60%. Comparing base (6965960) to head (0f0121b). Report is 488 commits behind head on main.

Files	Patch %	Lines
src/GreenDonut/src/Core/TaskCache.cs	84.09%	7 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4566      +/-   ##
==========================================
- Coverage   78.98%   76.60%   -2.39%     
==========================================
  Files        2903     2541     -362     
  Lines      139771   127086   -12685     
==========================================
- Hits       110397    97348   -13049     
- Misses      29374    29738     +364     

Flag	Coverage Δ
unittests	76.60% <87.50%> (-2.39%)	:arrow_down:

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[michaelstaib]

Replaced by #7382