Cosmos Repository Pattern

Skill: Cosmos Repository Pattern with Redis Cache

When to Use

Adding a new entity type that needs durable persistence with fast reads.

Pattern

1. Model: Add Id and PartitionKey properties to the entity class
2. Cosmos Repo: Create a concrete class extending CosmosRepositoryBase<T>. Override PrepareForCosmos to set Id + PartitionKey
3. DI Wiring: Register concrete repo as singleton, then register CachedRepository<T> as IRepository<T> with Redis key functions
4. Test Fixture: Add RedisBackedRepository<T> registration in ChargebackApiFactory.cs

Template

// 1. Model
public sealed class MyEntity {
    public string Id { get; set; } = string.Empty;
    public string PartitionKey { get; set; } = "my-entity";
    // ... fields
}

// 2. Repo
public sealed class CosmosMyEntityRepository : CosmosRepositoryBase<MyEntity> {
    public CosmosMyEntityRepository(ConfigurationContainerProvider p, ILogger<CosmosMyEntityRepository> l)
        : base(p, "my-entity", l) { }
    protected override void PrepareForCosmos(MyEntity e) {
        e.Id = e.SomeId;
        e.PartitionKey = "my-entity";
    }
}

// 3. Program.cs
builder.Services.AddSingleton<CosmosMyEntityRepository>();
builder.Services.AddSingleton<IRepository<MyEntity>>(sp =>
    new CachedRepository<MyEntity>(
        sp.GetRequiredService<CosmosMyEntityRepository>(),
        sp.GetRequiredService<IConnectionMultiplexer>(),
        id => $"my-entity:{id}",
        entity => entity.SomeId,
        sp.GetRequiredService<ILogger<CachedRepository<MyEntity>>>()));

// 4. Test fixture (ChargebackApiFactory.cs)
RemoveService<IRepository<MyEntity>>(services);
services.AddSingleton<IRepository<MyEntity>>(
    new RedisBackedRepository<MyEntity>(Redis, id => $"my-entity:{id}", e => e.SomeId, "my-entity:*"));

Key Constraints

• Cosmos partition key value must match the PartitionKey property default and the string in PrepareForCosmos
• Redis key function in CachedRepository must match RedisKeys.* patterns
• GetAllAsync queries Cosmos (not Redis scan) for completeness
• CacheWarmingService.cs must be updated to warm the new entity type on startup