![AGAIN PROTOCOLSTOTHE RESCUE
• Similar toTypedDatabaseItem but returns a row type of Codable, de-
serialized according to the type specified in the data row
Library Code public protocol PossibleItemTypes {
static var types: [Codable.Type] { get }
}
public struct PolymorphicDatabaseItem<RowIdentity : DynamoRowIdentity,
PossibleTypes : PossibleItemTypes> : Decodable {
...
}](https://image.slidesharecdn.com/scw3-180224052508/85/Swift-Micro-services-and-AWS-Technologies-19-320.jpg)
Swift Micro-services and AWS Technologies
- 1. SWIFT MICRO-SERVICES AND AWSTECHNOLOGIES Simon Pilkington Senior Software Engineer CoreTechnology AmazonVideo
- 2. ABOUT ME • 4 years helping architect, build and maintain frameworks for Amazon.com • Recently moved to CoreTechnology in AmazonVideo • Grew up in Melbourne,Australia
- 3. WHY SWIFT?
- 4. WHY IS JAVA PREVALENT? • Not significant learning curve • Harder to make mistakes than C++ • Enables higher developer velocity to create
- 5. WHY LOOK BEYOND JAVA? Build Logic What's included This package includes tools to help with: • Code Coverage (JaCoco, PIT) • Code Style (Checkstyle and matching IntelliJ formatter) • Code Quality (FindBugs, PMD, Copy Paste Detector, JDepend).
- 6. CODE GENERATION FOR SWIFT SERVICE • Code Generation of model objects, operation stubs and unit tests • Use Codable conformance for serialization and de-serialization • Swagger document can also be passed to Cloud Formation to create an API Gateway to front the service. Generated Code /** Handler for the HelloWorld operation. - Parameters: - input: The validated HelloWorldRequest object being passed to this operation. - context: The activities context provided for this operation. - Returns: The HelloWorldResponse object to be passed back from the caller of this operation. Will be validated before being returned to caller. */ func handleHelloWorld(input: HelloWorldModel.HellowWorldRequest, context: HellowWorldActivitiesContext) -> HelloWorldModel.HellowWorldResponse { return HelloWorldModel.HelloWorldResponse(greeting: "Hello (input.name)") }
- 7. RUNTIME • Initial proof of concept as a container running on ECS • Using an implementation of IBM’s LoggerAPI to write logs to Cloudwatch • Retrieve AWS credentials from the container with automatic credential rotation • Manages health checks, unresponsive containers are automatically replaced
- 8. DATABASE SERIALIZATION Code Code struct Fruit: Codable { let fruitID: FruitID let accessRole: AccessRole let sweet: Int let sour: Int } struct Location: Codable { let locationID: LocationID let fruitID: FruitID let locationPath: String let locationType: LocationType let checksum: Int let checksumType: ChecksumType }
- 9. • Large datasets or fast concurrent access more suited to NOSQL databases • Database schema based around data access patterns to enable efficient queries
- 10. • DynamoDb’s DynamoDBMapper in the Java AWS SDK implements optimistic locking by managing an invisible row version attribute • Currently there is a pull request to implement polymorphic tables similarly using inheritance and managing an invisible subclass attribute
- 11. But Inheritance…
- 12. PROTOCOLSTOTHE RESCUE! Probably look familiar Swift Language public protocol Encodable { public func encode(to encoder: Encoder) throws } public protocol Decodable { public init(from decoder: Decoder) throws } public typealias Codable = Decodable & Encodable
- 13. DYNAMO SPECIFIC ENCODING JSON { "Name": {"S": "Citrus"} "Description": {"S": "They’re alright."} } DynamoDb Codable Object Codable Object DynamoEncoder JSONEncoder DynamoDecoder JSONDecoder
- 14. OPERATION IMPLEMENTATION Code func handleRegisterFamily(input: FruitModel.FamilyAttributes, context: FruitActivitiesContext) throws -> FruitModel.FamilyIdentity { let currentID = context.idGenerator() let partitionKey = familyKeyPrefix + currentID let key = DefaultIdentityCompositePrimaryKey(partitionKey: partitionKey, sortKey: partitionKey) let newDatabaseRow = TypedDatabaseItem.newItem(withKey: key, andValue: input) try context.dynamoClient.putItem(newDatabaseRow) return FruitModel.FamilyIdentity(familyID: partitionKey) }
- 15. TYPEDDATABASEITEM • Handles row type, versioning, create and last modified timestamps. • Accepts a row value conforming to Codable • By default a newTypedDatabaseItem will fail to overwrite an existing row • CompositePrimaryKey defines row identity - partition and sort keys; generic in a protocol that defines the key attribute names
- 16. Library Code public struct TypedDatabaseItem<RowIdentity : DynamoRowIdentity, RowType : Codable>: Codable { ... public init(from decoder: Decoder) throws { let values = try decoder.container(keyedBy: CodingKeys.self) let storedRowTypeName = try values.decode(String.self, forKey: .rowType) self.createDate = try values.decode(Date.self, forKey: .createDate) // get the type that is being requested to be decoded into let requestedRowTypeName = getTypeRowIdentity(type: RowType.self) // if the stored rowType is not what we should attempt to decode into guard storedRowTypeName == requestedRowTypeName else { // throw an error to avoid accidentally decoding into the incorrect type throw SwiftDynamoError.typeMismatch(expected: storedRowTypeName, provided: requestedRowTypeName) } self.compositePrimaryKey = try CompositePrimaryKey(from: decoder) self.rowStatus = try RowStatus(from: decoder) self.rowValue = try RowType(from: decoder) self.canOverwriteExistingRow = false self.onlyOverwriteVersionNumber = nil } }
- 17. • createUpdatedItem function creates a new instance with updated last modified timestamp and incremented row version. • By default will fail to overwrite a row version other than the version it was created from Code let updatedFruitRow = fruitDatabaseItem.createUpdatedItem(withValue: updatedFruitAttributes) do { try context.dynamoClient.putItem(updatedAccountRow) } catch SwiftDynamoError.conditionalCheckFailed(_) { // handle the error }
- 18. BUT WHAT ABOUT QUERIES?
- 19. AGAIN PROTOCOLSTOTHE RESCUE • Similar toTypedDatabaseItem but returns a row type of Codable, de- serialized according to the type specified in the data row Library Code public protocol PossibleItemTypes { static var types: [Codable.Type] { get } } public struct PolymorphicDatabaseItem<RowIdentity : DynamoRowIdentity, PossibleTypes : PossibleItemTypes> : Decodable { ... }
- 20. A FINAL ODETO PROTOCOLS Generated Code public protocol LocationShape { associatedtype LocationTypeType : CustomStringConvertible associatedtype ChecksumTypeType : CustomStringConvertible var locationPath: String { get } var locationType: LocationTypeType { get } var checksum: String { get } var checksumType: ChecksumTypeType { get } func asFruitModelLocation() throws -> Location } Code extension SaladModel.Location : FruitModel.LocationShape {} ... let location = try input.location.asFruitModelLocation()