在 Coredata 中存储自定义 Class 类型数组

Question

I am trying to store custom class type array in coredata.

What I've got setup is an Entity called Node with properties value of type string and children of type Transformable . The children property is supposed to store an array of type Node as in the code below.

public class Node: NSManagedObject {

    @nonobjc public class func fetchRequest() -> NSFetchRequest<Node> {
        return NSFetchRequest<Node>(entityName: "Person")
    }

    @NSManaged public var children: [Node]?
    @NSManaged public var value: String?

}

.xcdatamodel setup:

Currently the app crashes with error message "This decoder will only decode classes that adopt NSSecureCoding. Class 'Node' does not adopt it." So I tried it with String array instead of Node array and it seems to work.

I'm guessing something extra needs to be done to store Custom array type.

Answer 1

It sounds like you want a recursive data structure, where each node can have many other nodes as children and another node as its parent. This is what CoreData relationships are for.

Under your Node entity:

1. Add a relationship children of type "To Many" with destination Node . No inverse.
2. Add a relationship parent of Type "To One" with destination Node , set its inverse to children
3. Go back to the children relationship and set its inverse to parent
4. Consider what the delete rules should be. I suggest "Cascade" for children , meaning if you delete a parent all of its children are deleted too. "Nullify" makes sense for parent , meaning if you delete a child it just removes the parent's connection to that one child.