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Purpose of Store

The Store serves as a mediator for your application’s data flow. It provides efficient and consistent data management. Its primary purposes are:

  • Data Orchestration: Manages the flow of data between the network, memory cache, and local storage (SourceOfTruth).
  • Efficient Caching: Handles in-memory and disk caching strategies to optimize data retrieval, reduce latency, and minimize unnecessary network requests.
  • Data Consistency: Guarantees consistency across all local data sources by synchronizing updates and, if a Validator is provided, ensuring that stale or invalid data is not served to consumers.
  • Flexible Validation: Provides configurable validation mechanisms to ensure data integrity and freshness according to your app’s specific needs.

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APIs

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Store

Store has the following structure:

interface Store<Key : Any, Output : Any> {
  fun stream(request: StoreReadRequest<Key>): Flow<StoreReadResponse<Output>>
  suspend fun clear(key: Key)
  suspend fun clearAll()
}
Key
Any
required

The type representing the key used to identify the data item.

Output
Any
required

The type representing the domain data model representation of the item being retrieved.

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stream

A function that returns a Flow of StoreReadResponse.

request
StoreReadRequest<Key>
required

The request configuration for the data retrieval.

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clear

A function that clears the data item identified by the given key.

This method only removes data from the memory cache and source of truth. It will not update the remote data source.

key
Key
required

The key identifying the data item to be cleared.

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clearAll

A function that clears all data items.

This method only removes data from the memory cache and source of truth. It will not update the remote data source.

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Key Components

The RealStore is the default implementation of the Store interface. It’s composed of the following components:

  1. FetcherController: Responsible for efficient network operations.

    • Prevents duplicate network calls for the same data.
    • Shares responses among multiple requesters.
    • Manages network request lifecycles.

  2. SourceOfTruthWithBarrier: Wraps the SourceOfTruth.

    • Synchronizes read and write operations.
    • Provides persistent data storage.
    • Maintains data consistency.

  3. Memory Cache: Fast, temporary storage.

    • Provides quick data retrieval without hitting disk or network.
    • Reduces latency.
    • Automatically manages memory usage.

  4. Converter: Transforms data between network, local database, and domain data model types.

    • Facilitates data compatibility between different layers of the Store.

  5. Validator: Validates cached data to ensure it’s still valid.

    • Prevents serving stale or invalid data to consumers.

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Data Flow

Here’s how Store manages data flow through your app:

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Reading Data

1

Memory Cache Check

Checks if the requested data is present and valid in the in-memory cache.

val cachedToEmit = if (request.shouldSkipCache(CacheType.MEMORY)) {
    null
} else {
    val output: Output? = memCache?.getIfPresent(request.key)
    val isInvalid = output != null && validator?.isValid(output) == false
    when {
        output == null || isInvalid -> null
        else -> output
    }
}
A

Validation

If data is found, it’s validating using the Validator. If a Validator is not provided, the data is considered valid.

B

Emission

Valid data is emitted immediately to the consumer.

cachedToEmit?.let { it: Output ->
  emit(StoreReadResponse.Data(value = it, origin = StoreReadResponseOrigin.Cache))
}
2

Decide Data Source

Determines whether to read from the SourceOfTruth, fetch from the network, or both. Emits NoNewData if neither SourceOfTruth nor network fetch is requested.

if (sourceOfTruth == null && !request.fetch) {
  emit(StoreReadResponse.NoNewData(origin = StoreReadResponseOrigin.Cache))
  return@flow
}
3

Source of Truth Read

If a SourceOfTruth is configured and not skipped, attempts to read data from it.

if (request.fetch) {
  diskNetworkCombined(request, sourceOfTruth)
} else {
  sourceOfTruth.reader(request.key, diskLock).transform { response -> ... }
}
A

Validation

If data is found, it’s validating using the Validator. If a Validator is not provided, the data is considered valid.

B

Emission

Valid data is emitted to the consumer.

C

Network Fetch Decision

If data is not found or invalid, decides whether to fetch from the network.

4

Network Fetch

If a network fetch is required, fetches data from the network.

val networkFlow = createNetworkFlow(request, networkLock)

The FetcherController ensures only one network call per key.

A

Data Handling

Fetched data is written to the SourceOfTruth and memory cache.

5

Combine and Emit Data

Combines the flows from the network and the source of truth to emit data in the correct order and origin to the subscribers.

emitAll(
  stream.transform { output: StoreReadResponse<Output> ->
    emit(output)
    // Update memory cache if needed
  },
)

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Writing Data

While the Store primarily focuses on reading data, it provides an internal write method for updating data in the cache and SourceOfTruth.

1

Update Memory Cache

Updates the in-memory cache with the new data.

memCache?.put(key, value)
2

Update Source of Truth

Writes the new data to the local storage (source of truth).

sourceOfTruth?.write(key, converter.fromOutputToLocal(value))
3

Error Handling

Catches any exceptions during the write operation and returns the appropriate result.

catch (error: Throwable) {
  StoreDelegateWriteResult.Error.Exception(error)
}

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Best Practices

  • Configure Memory Usage: Set appropriate memory cache sizes based on device capabilities and data volume. Implement cache eviction policies that align with your app’s data freshness requirements.
  • Implement Error Handling: Define clear error recovery paths for network failures, cache misses, and data corruption. Use the Fetcher retry mechanisms for transient network failures.
  • Ensure Data Consistency: Set up the Source Of Truth as the single source of truth for critical data. Implement validation rules that catch data inconsistencies early.
  • Optimize Network Usage: Batch related requests where possible. Configure appropriate cache TTLs to minimize unnecessary network calls.
  • Monitor Performance: Track cache hit rates, network request frequencies, and data refresh patterns. Adjust caching strategies based on real-world usage patterns.
  • Structure Keys Effectively: Design cache keys that are both unique and logical, avoiding collisions while maintaining readability. Consider namespacing keys for different data types.
OverviewMutable Store