Values added during editor mode are removed when starting playmode

I have nodes in my game, that have a List filled with connected nodes. I don’t want to manually add nodes to each other with drag and drop, but I want to connect all nodes that are currently selected in the editor. I wrote this script:

	[MenuItem("Node Tools/Connect Selected Nodes %g")]
	static void ConnectSelectedNodes() {
		List<AbstractNode> selectedNodes = new List<AbstractNode>();

		foreach (GameObject n in Selection.gameObjects) {
			if (n.GetComponent<AbstractNode>() != null) {


		foreach (AbstractNode n in selectedNodes) {
			foreach (AbstractNode c in selectedNodes) {
				if (n.gameObject != c.gameObject) {
					Undo.RecordObject(n, "Added connection");

The connection gets added in the inspector, but when I press play, every field in the array switches to “null” and stays like that after stopping the game.

I hope you guys can help me with this problem.

It would be good to see your AbstractNode class.

When calling n.AddConnection(c), are you changing any private variables, say, adding the other node to a list? Any fields you change must have an attribute [SerializeField] in front of it, or the changes won’t be saved for runtime.

If AbstractNode is a struct or a class instead of a MonoBehaviour script, it might also need to have the attribute [System.Serializable]. This makes the values appear in the Inspector, and I think it allows changes to be saved.

Does the object in question come from a prefab with values of its own?