iOS & Swift 공부 - Realm -> How to Save Data Using Realm (Create in CRUD)

• First, setup the necessary Data files in your project directory.
• The class you set up must be a subclass of "Object", which is a class used to define Realm model objects.
• The properties of such class must have "@objc dynamic" declaration modifiers, so that Realm can detect changes of those variables during runtime.

• So each "Category" has a 1-to-many relationship with a List of Items.
• However, Realm does not define the inverse relationship automatically.
• For instance, in a Todo App, each category will have a separate array of (todo) items. To declare this relationship, we can use a class called "List", which is the container type in Realm used to define to-many relationships.

• Here, we can see that each Item has an inverse relationship to a Category called the parentCategory. So, each Item has a parentCategory.

• Initialize Realm for usage. Making a Realm( ) instance is essential for every class file.

@IBAction func addButtonPressed(_ sender: UIBarButtonItem) {
        
        var textField = UITextField()
        
        let alert = UIAlertController(title: "Add New Category", message: "", preferredStyle: .alert)
        
        let action = UIAlertAction(title: "Add Category", style: .default) { (action) in
        
            let newCategory = Category()
            newCategory.name = textField.text!
            
            self.categories.append(newCategory)
            self.save(category: newCategory)
        }
        alert.addTextField { (alertTextField) in
            alertTextField.placeholder = "Category Name"
            textField = alertTextField
        }
        alert.addAction(action)
        present(alert, animated: true, completion: nil)
    }

func save(category: Category) {
        
        do {
            //try context.save()
            try realm.write {
                realm.add(category)
                
            }
        } catch {
            print("Error saving new category : \(error)")
        }
        self.tableView.reloadData()
    }

→ realm.write { } can throw an error, just like context.save( ) does with Core Date. Thus, we need to put it inside a do-catch statement.

• real.write { } is like saying, "we are beginning to write". The real part where we actually add data to the Realm data base is the realm.add( ) part.

// TodoListViewController

var selectedCategory: Category? {
    didSet {
        loadItems()
    }
}

...
if let currentCategory = self.selectedCategory {
       do {
           try self.realm.write {
                        
            let newItem = Item()
                        
            newItem.title = textField.text!
            newItem.isDone = false
                        
            currentCategory.items.append(newItem)
            }
        } catch {
            print("Error saving new items \(error)")
         }
       }
  self.tableView.reloadData()
}

// Item.swift
class Category: Object {
    
    @objc dynamic var name: String = ""

    let items = List<Item>()
}

• Notice we are "appending" in this case. But we are not appending to the Item data type. We are tapping in to the currently selected category.