Deserializing an ordered custom collection-CodePudding

I have a class, which has as a property a collection of instances of another class:

class Inventory
{
    public List<InventoryItem> Items
    {
        get;
        set;
    }
}

InventoryItem has a few properties, including a DateTime Start, but I will omit its implementation for brevity.

The class above deserializes correctly out of the box, with Newtonsoft.Json:

string serialization = "{ 'Items': [ { 'Amount': 1, 'Start': '2018-01-14T00:00:00', 'Id': 0 } ] }";
var inventory = JsonConvert.DeserializeObject<Inventory>( serialization );
Assert.AreEqual( inventory.Items.First().Amount, 1 );

However, what I want is to sort Items, by Start, as follows:

class Inventory
{
    private List<InventoryItem> _inventoryItems = new();

    public List<InventoryItem> Items
    {
        // order them before returning
        get => this._inventoryItems.OrderBy( t => t.Start ).ToList();
        set => this._inventoryItems = value;
    }
}

Now the deserialization fails. The Inventory class is created, but no inventory items are created. I can make this work with a custom converter, but it seems to me there ought to be an easier way.

CodePudding user response：

My best guess as to what's happening here is Json.NET is setting your property to a new instance of List<InventoryItem> and using Add to add each item to the list.

In your getter, you're ordering it then using .ToList() to convert it back to a list. This creates a new instance of List<InventoryItem>(), which means the items are getting added to a different list each time, all of which are being thrown away.

However, List<T> does have a .Sort() method you can utilize. Unfortunately though it returns void, so we can't make it a one-liner. In your case, the implementation of this would look a little like this:

class Inventory
{
    private List<InventoryItem> _inventoryItems = new();

    public List<InventoryItem> Items
    {
        // order them before returning
        get 
        {
            this._inventoryItems.Sort((x, y) => x.Start > y.Start ? 1 : -1);
            return this._inventoryItems;
        }
        set => this._inventoryItems = value;
    }
}

A little bit of an explanation on the Sort() method; It will always sort ascending. Returning 1 means that x is greater than y, returning -1 means that y is greater than x, and returning 0 means they're equal. In this example, it's sorting by Start ascending. To sort descending, you can either flip the sign or flip the values in the ternary statement.