How to update a field "type-safe" in a deeply nested array with C# MongoDb driver?

Question

I am trying to update individual fields in a deeply nested array.

    public class Maker
    {
        public int Id { get; set; }
        public List Vehicles { get; set; }
    }

    public class Vehicle
    {
        public int Id { get; set; }
        public int Price { get; set; }
        public List Parts { get; set; }
    }

    public class Part
    {
        public int Id { get; set; }
        public string Name { get; set; }
    }

Updating a field in a level-1 array works like a charm. Updating a field in a level-2 array fails.

 public void UpdateNestedArrayFields()
    {
        var client = new MongoClient();
        var db = client.GetDatabase("test");
        var makers = db.GetCollection("makers");

        // Create a maker and add a vehicle
        var newPart = new Part() { Id = 34, Name = "Wheel" };
        var newVehicle = new Vehicle() { Id = 17, Price = 1000, Parts = new List() { newPart } };
        var newMaker = new Maker() { Id = 5, Vehicles = new List() { newVehicle } };

        // Update vehicle's price (WORKS)
        makers.FindOneAndUpdate(
            m => m.Id == newMaker.Id && m.Vehicles.Any(v => v.Id == newVehicle.Id),
            Builders.Update.Set(m => m.Vehicles[-1].Price, 2000));

        // Update part's name (**FAILS**)
        makers.FindOneAndUpdate(
            m => m.Id == newMaker.Id && m.Vehicles.Single(v => v.Id == newVehicle.Id).Parts.Any(p=> p.Id == newPart.Id),
            Builders.Update.Set(m => m.Vehicles[-1].Parts[-1].Name, "Tire"));
    }

I understand that multiple positional operators are not supported, so my last line (m.Vehicles[-1].Parts[-1].Name) is kind of crap.

Obviously I am not the only one having this problem and I found different solutions like this or that. However, none of them is type safe. The resulting code is pretty ugly and error prone.

So I was wondering: Is there any way to redesign my code so it is type safe?

I am using MongoDb 4.0.9 and C# driver 2.11.5.

Edit (01-11-2020): For anybody interested, I found this really nice extension by Massimiliano Kraus, which is a bit outdated (2017), but is still working and turned out to be a huge help. Thank you, Massimiliano! MongoDB.DeepUpdater.CSharp

user_4368485 · Answer

in order to update nested arrays like this, you need to use the array filters feature of mongodb.

the needed mongo query is this:

db.Maker.update(
    {
        "_id": 5
    },
    {
        $set: { 'Vehicles.$[v].Parts.$[p].Name': 'Tyre' }
    },
    {
        arrayFilters: [
            { 'v._id': { $eq: 17 } },
            { 'p._id': { $eq: 34 } }
        ]
    }
)

the c# driver is not capable of generating the above in a strongly-typed fashion. have a look at this article for an alternative semi-typed solution to running advanced queries like the above.

user_3862698 · Answer

There is an other possible and more typed version of typed nested array update. it not fully typed, but it is closer to what u need.

its also using ArrayFilters but in more typed fashion

this code is coming straight from application that I'm working on.

var filter = Builders.Filter.Eq(s => s.Id, eventId);

var settingsPath = @$"{nameof(EventModel.EventLayout)}.{nameof(EventLayoutSetting.Pages)}.$[page].{nameof(Page.Components)}.$[component].{nameof(Component.Settings)}";
var update = Builders.Update.
                     Set(settingsPath, settings);

var dbResult = await eventsCollection.UpdateOneAsync(filter, update, new UpdateOptions 
            {
                ArrayFilters = new List 
                {
                    new BsonDocumentArrayFilterDefinition (new BsonDocument($"page.{nameof(Page.PageId)}",pageId)),
                    new BsonDocumentArrayFilterDefinition (new BsonDocument($"component.{nameof(Component.ComponentId)}",componentId))
                }
            });

How to update a field "type-safe" in a deeply nested array with C# MongoDb driver?

2 Answers