不能在MongoDb C＃上使用Linq和嵌套类List <>

Question

I have the following classes:

public class Company
{
   [BsonId]
   public string dealerId = null;

   public List<Dealer> dealers = new List<Dealer>();
}

public class Dealer
{        
   public string dId = null;          
   public int dIndex = -1;

   public List<AutoStore> stores = new List<AutoStore>();
}

public class AutoStore
{
   public string type = null; 
   public  Dictionary<string, object> data = new Dictionary<string, object>();
}

I am able to store the Company class objects in Mongo with Insert() . The problem is when I search for a document and try to use LINQ on the List<> items. I constantly get an exception .

var query =  collection.AsQueryable<Company>()
                 .Where(cpy =>
                     cpy.dealers.Where(dlr => 
                         dlr.stores.Count == 1).Count() > 0) ;

Running this code I get:

System.NotSupportedException: Unable to determine the serialization information for the expression: Enumerable.Count

I just started using Mongo today, but I thought the LINQ support was more mature. Can anyone tell me if I can do a nested array query like I've done with C# and LINQ ?

As soon as I remove the Where() on any of the List<> , that exception isn't thrown

Answer 1

Going by your exception the problem area is within where you are doing Where statements.

As I said in my comment. Try to do:

var v = collection.AsQueryable<Company>().Where(cpy => cpy.Dealers.Any(dlr => dlr.Stores.Count == 1));

You are currently doing something like:

var dealers = collection.AsQueryable<Company>().Select(cpy => cpy.Dealers);
var dealersWithStores = dealers.Where(dealer => dealer.Stores.Count == 1);

You are then checking if there are any dealers with stores by calling count and checking if that is more than 0 to get your bool in the where. All of this is the same as calling IEnumerable.Any() . See if this works? :)

Answer 2

You could write you query more efficiently as

var query =  collection.AsQueryable<Company>()
                 .Where(c => c.dealers.Any(d => d.stores.Count == 1);

If the Mongo querty provider is struggling to support IList , you might find

var query =  collection.AsQueryable<Company>()
                 .Where(c => c.dealers.Any(d => d.stores.Count() == 1);

works better. If so, reports of the maturity of MongoDBs query provider are exaggerated.