Get all elements from Lists inside a List

Question

I have following data model:

    public class Customer
    {
        [BsonId]
        public int CustomerId { get; set; }
        public string Name { get; set; }
    }

    public class Order
    {
        [BsonId]
        public int OrderId { get; set; }
        [BsonRef("customers")] 
        public Customer Customer { get; set; }
    }

    public class Cart
    {
        [BsonId]
        public int CartID { get; set; }
        public List<Order> OrderList { get; set; }
    }

Now I want to access the customers via queries on my cart collection. I tried something like this:

var collectionCarts = db.GetCollection<Cart>("carts");
var result = collectionCarts.Include("OrderList.Customer").Find(x => x.OrderList[0].Customer.CustomerId == 2);

However, all attempts result in an empty customer object. My database, which I checked with the LiteDB-Viewer seems to be OK.

Romano Zumbé · Answer 1 · 2017-07-12T07:30:38.017

5

You could get the Customers like this:

using System.Linq;

collectionCarts.SelectMany(c => c.OrderList.Select(o => o.Customer));

edited Jul 12 '17 at 07:30

answered Jul 12 '17 at 07:07

Romano Zumbé

7,893
4
33
55

Thanks for your quick reply. What is the the `carts` objects which you start with? `var carts = db.GetCollection("carts");` ? – h0ch5tr4355 Jul 12 '17 at 07:11
It's showing that there is no definition for the method "Select" – h0ch5tr4355 Jul 12 '17 at 07:12
You need to include the namespace `System.Linq` (See my edit). I've also changed to `collectionCarts`. I thought that this would be an enumerable collection of `Cart` objects. – Romano Zumbé Jul 12 '17 at 07:16
I have Linq added. The syntax seems to work, but there are still empty customer objects (null) as they cant be extracted from the litedb database correctly I assume. – h0ch5tr4355 Jul 12 '17 at 07:21
That will have some other reason. This Linq query will give you all `Customer` objects with the `CustomerId` 2 from all `OrderLists` from all `Carts` in the collection – Romano Zumbé Jul 12 '17 at 07:23
Yes I checked this with `var allCarts = collectionCarts.FindAll();` With your expression on the `allCarts`object the correct objects are excluded, but the the customer field is null. – h0ch5tr4355 Jul 12 '17 at 07:25
I didn't use LightDB yet. Is there perhaps an issue with lazy loading? – Romano Zumbé Jul 12 '17 at 07:27
I don't know, but it seems to not store sub-documents (customers) in the returning objects. – h0ch5tr4355 Jul 12 '17 at 07:35
Seems like another question to me ;-) – Romano Zumbé Jul 12 '17 at 07:47
Thanks! SelectMany is the answer – Juan Stoppa Apr 01 '21 at 23:43

score 0 · Answer 2 · answered Jul 12 '17 at 07:29

0

Are you trying to check only for the first item in the list, or for any item in the list? Because in your query, you are explicitly querying for the first one only.

If not (as I assume), try something like this:

var result = collectionCarts.Include("OrderList.Customer").
                    Find(x => x.Select(v => v.OrderList).Select(v =>v.Customer).
                                     Select(v => v.CustomerId).ToList().Contains(2));

answered Jul 12 '17 at 07:29

AvrahamL

181
4
16

Again an error that there is no definiton for `Select` – h0ch5tr4355 Jul 12 '17 at 07:37
I see.... How about: var result = collectionCarts.Include("OrderList.Customer").Find(Query.Contains("OrderList.$.Customer.$.CustomerId", 2)); – AvrahamL Jul 12 '17 at 07:50
This doesn't bring my any results. – h0ch5tr4355 Jul 12 '17 at 07:55
Or even: var result = collectionCarts.Include("OrderList.Customer").Select(v => v.OrderList).Select(v => v.Customer).Find(x => x.CustomerId == 2); – AvrahamL Jul 12 '17 at 07:56
There is the `Select not found` problem again – h0ch5tr4355 Jul 12 '17 at 07:57

Get all elements from Lists inside a List

2 Answers2