realm - `Add` 和 `Create` 有什么区别

Question

文档指出了显而易见的事实，即:

add(_:update:) Adds or updates an object to be persisted it in this Realm.
create(_:value:update:) Creates or updates an instance of this object and adds it to the Realm populating the object with the given value.

但我不太明白有什么区别吗？

Answer 1

add 将立即更新整个对象，因此存在丢失属性的危险。 create可以通过显示属性名来更新对象的部分信息。

假设 CheeseBook 已保存如下。

    let cheeseBook = Book()
    cheeseBook.title = "cheese recipes"
    cheeseBook.price = 9000
    cheeseBook.id = 1

    //update 1 - title will be empty
    try! realm.write {
        let cheeseBook = Book()
        cheeseBook.price = 300
        cheeseBook.id = 1
        realm.add(cheeseBook, update:true)            
    }

    //update2 - title will stay as cheese recipes
    try! realm.write {
        realm.create(Book.self, value:["id":1, "price":300], update:true)
    }