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SWGQL02: Unused DataLoader interface

Overview​

Rule ID: SWGQL02
Category: GraphQL
Severity: Info
Status: Enabled by default

Description​

This rule identifies DataLoader interfaces that implement GreenDonut.IDataLoader<,> but don't appear to be referenced anywhere in the current compilation. This helps detect potentially unused DataLoaders that may have been left behind during refactoring.

When This Rule Triggers​

The analyzer reports a diagnostic when:

  • An interface implements GreenDonut.IDataLoader<TKey, TValue>
  • The interface is not referenced (instantiated or used) anywhere in the compilation
  • GreenDonut is available in the project dependencies

Why This Matters​

DataLoaders are a key performance optimization pattern in GraphQL to batch database queries and prevent N+1 query problems. Unused DataLoaders typically indicate:

  • Code that was removed during refactoring
  • Dead code that should be cleaned up
  • A DataLoader that was registered but never used

Cleaning up unused DataLoaders reduces complexity and maintenance burden.

How to Fix​

Option 1: Use the DataLoader​

If you have a DataLoader that should be used, ensure it's:

  • Registered in your dependency injection container
  • Used in field resolvers
// ✅ CORRECT - Used in a resolver
public class UserResolver
{
    public async Task<User?> GetUserAsync(
        [Parent] Post post,
        [DataLoader] UserDataLoader userDataLoader)
    {
        return await userDataLoader.LoadAsync(post.UserId);
    }
}

Option 2: Remove the unused DataLoader​

If the DataLoader is no longer needed, simply delete the interface:

// ❌ Unused interface - remove it
public interface IUnusedDataLoader : IDataLoader<int, string>
{
}

Example​

using GreenDonut;

// ⚠️ SWGQL02 - This interface appears unused in the compilation
public interface IUserDataLoader : IDataLoader<int, User>
{
}

// ✅ CORRECT - This interface is used
public interface IPostDataLoader : IDataLoader<int, Post>
{
}

public class PostResolver
{
    public async Task<User?> GetAuthorAsync(
        [Parent] Post post,
        [DataLoader] IPostDataLoader postDataLoader)
    {
        return await postDataLoader.LoadAsync(post.Id);
    }
}

Configuration​

This rule is informational by default. To treat it as a warning or error:

[*.cs]
dotnet_diagnostic.SWGQL02.severity = warning

To disable it:

[*.cs]
dotnet_diagnostic.SWGQL02.severity = none
  • None

See Also​