Continuing with our clean architecture, let’s write a simple Todo CoreData Datasource in swift. Our applications repository method would use the DataSource, in this case, the TodoCoreDataSource. Here is the proposed files and their locations:
├─Core
└─Data
├─DataSource
│ ├── TodoDataSource.swift
│ └─CoreData
│ ├── Main.xcdatamodeld
│ └── TodoCoreDataSourceImpl.swift
└─Repository
└── TodoRepositoryImpl.swift
├─Presentation
└─Domain
├─Model
│ └── Todo.swift
├─Error
│ └── TodoError.swift
└─Repository
└── TodoRepository.swift
Let’s first specify our Domain Model and Repository. We need a domain model because we can’t always control what our data source model looks and operates like.
struct Todo: Identifiable{
let id: UUID
let title: String
let isCompleted: Bool
}
Mapping between these two models would need to take place in our data source.
protocol TodoDataSource{
func getAll() async throws -> [Todo]
func getById(_ id: UUID) async throws -> Todo?
func delete(_ id: UUID) async throws -> ()
func create(todo: Todo) async throws -> ()
func update(id: UUID, todo: Todo) async throws -> ()
}
This time around we need a persistence framework for our data source. Here we’re going to use Core Data to save your application’s permanent data for offline use.
Create a CoreData Model by adding a new file and choosing Core Data -> Data Model and creating at TodoCoreDataEntity:
To use the CoreData Main Model we can create a data source that conforms to the TodoDataSource and uses the NSPersitanceContainer.
import Foundation
import CoreData
struct TodoCoreDataSourceImpl: TodoDataSource {
let container: NSPersistentContainer
init(){
container = NSPersistentContainer(name: "Main")
container.loadPersistentStores { description, error in
if error != nil {
fatalError("Cannot Load Core Data Model")
}
}
}
func getAll() throws -> [Todo]{
let request = TodoCoreDataEntity.fetchRequest()
return try container.viewContext.fetch(request).map({ todoCoreDataEntity in
Todo(
id: todoCoreDataEntity.id!,
title: todoCoreDataEntity.title!,
isCompleted: todoCoreDataEntity.is_completed
)
})
}
func getById(_ id: UUID) throws -> Todo?{
let todoCoreDataEntity = try getEntityById(id)!
return Todo(
id: todoCoreDataEntity.id!,
title: todoCoreDataEntity.title!,
isCompleted: todoCoreDataEntity.is_completed
)
}
func delete(_ id: UUID) throws -> (){
let todoCoreDataEntity = try getEntityById(id)!
let context = container.viewContext;
context.delete(todoCoreDataEntity)
do{
try context.save()
}catch{
context.rollback()
fatalError("Error: \(error.localizedDescription)")
}
}
func update(id: UUID, todo: Todo) throws -> (){
let todoCoreDataEntity = try getEntityById(id)!
todoCoreDataEntity.is_completed = todo.isCompleted
todoCoreDataEntity.title = todo.title
saveContext()
}
func create(todo: Todo) throws -> (){
let todoCoreDataEntity = TodoCoreDataEntity(context: container.viewContext)
todoCoreDataEntity.is_completed = todo.isCompleted
todoCoreDataEntity.title = todo.title
todoCoreDataEntity.id = todo.id
saveContext()
}
private func getEntityById(_ id: UUID) throws -> TodoCoreDataEntity?{
let request = TodoCoreDataEntity.fetchRequest()
request.fetchLimit = 1
request.predicate = NSPredicate(
format: "id = %@", id.uuidString)
let context = container.viewContext
let todoCoreDataEntity = try context.fetch(request)[0]
return todoCoreDataEntity
}
private func saveContext(){
let context = container.viewContext
if context.hasChanges {
do{
try context.save()
}catch{
fatalError("Error: \(error.localizedDescription)")
}
}
}
}
and then lastly, our TodoRepositoryImpl would implement our TodoRepository and call our Datasource:
protocol TodoRepository {
func getTodos() async -> Result<[Todo], TodoError>
func getTodo(id: UUID) async -> Result<Todo? , TodoError>
func deleteTodo(_ id: UUID) async -> Result<Bool, TodoError>
func createTodo(_ todo: Todo) async -> Result<Bool, TodoError>
func updateTodo(_ todo: Todo) async -> Result<Bool, TodoError>
}
enum TodoError: Error{
case DataSourceError, CreateError, DeleteError, UpdateError, FetchError
}
import Foundation
struct TodoRepositoryImpl: TodoRepository{
var dataSource: TodoDataSource
func getTodo(id: UUID) async -> Result<Todo?, TodoError> {
do{
let _todo = try await dataSource.getById(id)
return .success(_todo)
}catch{
return .failure(.FetchError)
}
}
func deleteTodo(_ id: UUID) async -> Result<Bool, TodoError> {
do{
try await dataSource.delete(id)
return .success(true)
}catch{
return .failure(.DeleteError)
}
}
func createTodo(_ todo: Todo) async -> Result<Bool, TodoError> {
do{
try await dataSource.create(todo: todo)
return .success(true)
}catch{
return .failure(.CreateError)
}
}
func updateTodo(_ todo: Todo) async -> Result<Bool, TodoError> {
do{
try await dataSource.update(id: todo.id, todo:todo)
return .success(true)
}catch{
return .failure(.UpdateError)
}
}
func getTodos() async -> Result<[Todo], TodoError> {
do{
let _todos = try await dataSource.getAll()
return .success(_todos)
}catch{
return .failure(.FetchError)
}
}
}
