Coredata storage to do list

Check... When creating the project CoreData, The system will automatically AppDelegate The generated code , And generate a xcdatamodeld file , It doesn't matter if you don't check it , New one checked CoreData Project , Copy the generated code and create it yourself xcdatamodeld file .

  stay xcdatamodeld New in the file ENTITIES Replace the original Todo Structure , And add two Attribute Element and select type , You can set the default value on the right function panel , The bottom layer of the system will generate a class.

 

 

 

  stay AppDelegate You can see the generated persistence container persistentContainer and SaveContext Method is used to judge whether the data has changed and store the data .

Open again through the sandbox address Application Support The file shows sqlite Database files , open Todos.sqlite file （ Suggest using DB Browser for SQLite App open ） 

 

 

You can see the database structure and saved data  

  Instantiate an empty container , Add a to-do and save

let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext// obtain appDelegat Object to get the contents of the container 
        let todo = Todo(context: context)// Instantiate an empty container 
        todo.name = name
        todos.append(todo)
        
        (UIApplication.shared.delegate as! AppDelegate).saveContext()// Judge whether the data is changed and save 
        
        tableView.insertRows(at: [IndexPath(row: todos.count - 1, section: 0)], with: .automatic)

Delete the to-do and save

First delete the local data , Then delete the memory data , Because the local is deleted through memory , For example, data [1,2,3] If you delete the memory first 1 Then the memory will become [2,3] And the local memory is now based on the 1 individual

 

override func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCell.EditingStyle, forRowAt indexPath: IndexPath) {
        if editingStyle == .delete {
            // Delete the row from the data source
            context.delete(todos[indexPath.row])// First delete local , Delete memory again , Found locally through memory 
            todos.remove(at: indexPath.row)
            appDelegate.saveContext()
//            tableView.deleteRows(at: [indexPath], with: .fade)
            //saveData()
            tableView.reloadData()
        } else if editingStyle == .insert {
            // Create a new instance of the appropriate class, insert it into the array, and add a new row to the table view
        }
    }

Fixed usage fetches data

if let todos = try? context.fetch(Todo.fetchRequest()){
            self.todos = todos
        }else{
            print(" from SQLite Failed to get data from inside ")
        }// Fixed usage fetches data 

because context Not only in the new to-do list , So it can be proposed as a global variable

  Modify and delete the to-do list, call the function to save

appDelegate.saveContext()

Sort

The attributes stored in the database are unordered after sorting , So you need to be in ENTITY Add an attribute representing the sequence number （ Database migration ）

todos[indexPath.row].orderID = Int16(indexPath.row)
        appDelegate.saveContext()

  Assign sorting rules when retrieving data

let request = Todo.fetchRequest()
        request.sortDescriptors = [NSSortDescriptor(key: kOrderID, ascending: true)]
        
        if let todos = try? context.fetch(Todo.fetchRequest()){
            self.todos = todos
        }else{
            print(" from SQLite Failed to get data from inside ")
        }// Fixed usage fetches data