Implementing a Feature Store

To create a custom feature store, implement the FeatureStore interface. For convenience, it is highly recommended to extend AbstractFeatureStore, which handles most of the common logic and boilerplate.

Using AbstractFeatureStore

AbstractFeatureStore provides default implementations for group management, permission handling helper methods, and validation. You primarily need to implement the core CRUD operations.

class MyCustomFeatureStore : AbstractFeatureStore() {

    // Helper map to simulate a DB for this example
    private val db = mutableMapOf<String, Feature>()

    override suspend fun get(featureId: String): Feature? {
        return db[featureId]
    }

    override suspend fun getAll(): Map<String, Feature> {
        return db.toMap()
    }

    // Using the 'plusAssign' operator for creation (store += feature)
    override suspend fun plusAssign(feature: Feature) {
        if (feature.uid in db) {
            throw FeatureAlreadyExistsException(feature.uid)
        }
        db[feature.uid] = feature
    }

    // Using the 'minusAssign' operator for deletion (store -= featureId)
    override suspend fun minusAssign(featureId: String) {
         if (featureId !in db) {
            throw FeatureNotFoundException(featureId)
        }
        db.remove(featureId)
    }

    override suspend fun update(feature: Feature) {
         if (feature.uid !in db) {
            throw FeatureNotFoundException(feature.uid)
        }
        db[feature.uid] = feature
    }

    override suspend fun clear() {
        db.clear()
    }

    // ... implement other abstract methods ...
}

Verifying Your Implementation

It is critical to ensure your custom store behaves correctly. FF4K provides a Contract Test Suite that you can use to automatically verify your implementation against the expected behavior.

class MyCustomFeatureStoreTest : FeatureStoreContractTest() {
    override suspend fun createStore(): FeatureStore {
        // Return a fresh instance of your store for each test
        return MyCustomFeatureStore()
    }
}

This will run a suite of tests covering CRUD operations, toggling features, group operations, permissions, and concurrency.

Registering Your Store

Once implemented, pass your custom store to the ff4k configuration function.

suspend fun main() {
    val ff4k = ff4k(
        featureStore = MyCustomFeatureStore(),
        // ...
    ) {
        // ...
    }
}