Adapter

Definition

The Adapter pattern converts the interface of an existing class into the interface expected by the client, allowing incompatible components to collaborate. The adapter wraps the existing class and translates calls.

Diagram

classDiagram
    class ICacheService_TCacheItem_TKey {
        +GetOrAddAsync(key: TKey)
    }

    class ICacheService_TCacheItem {
        +GetOrAddAsync(key: string)
    }

    class TypedKeyCacheServiceAdapter {
        -inner : ICacheService_TCacheItem
        +GetOrAddAsync(key: TKey)
    }

    ICacheService_TCacheItem_TKey <|.. TypedKeyCacheServiceAdapter
    TypedKeyCacheServiceAdapter --> ICacheService_TCacheItem : delegates via key.ToString()

    class IBlobStorageClient {
        +DeleteObjectAsync()
        +HeadObjectAsync()
    }

    class AmazonS3Client {
        +DeleteObjectAsync()
        +GetObjectMetadataAsync()
    }

    class S3BlobClient {
        -s3Client : AmazonS3Client
    }

    IBlobStorageClient <|.. S3BlobClient
    S3BlobClient --> AmazonS3Client : adapts

Implementation in Granit

Adapter	File	Target interface	Adapted class
TypedKeyCacheServiceAdapter<TCacheItem, TKey>	src/Granit.Caching/TypedKeyCacheServiceAdapter.cs	ICacheService<TCacheItem, TKey>	ICacheService<TCacheItem> (string keys)
S3BlobClient	src/Granit.BlobStorage.S3/Internal/S3BlobClient.cs	IBlobStorageClient	AmazonS3Client (AWS SDK)
MailKitSmtpTransport	src/Granit.Notifications.Email.Smtp/MailKitSmtpTransport.cs	ISmtpTransport	SmtpClient (MailKit, sealed)

Rationale

TypedKeyCacheServiceAdapter enables strongly-typed keys (Guid, int, composite) while delegating to the existing string-key-based cache service. S3BlobClient isolates the framework from the AWS SDK, allowing provider changes (European hosting, MinIO) without touching the core.

Usage example

// Application uses typed keys -- the adapter converts to string
ICacheService<PatientDto, Guid> cache = serviceProvider
    .GetRequiredService<ICacheService<PatientDto, Guid>>();

PatientDto patient = await cache.GetOrAddAsync(
    patientId, // Guid -- converted to string by the adapter
    async ct => await db.Patients.FindAsync([patientId], ct),
    cancellationToken);

Further reading

• Adapter — refactoring.guru