MongoDB C# .NET Driver ASP.NET Core Unsupported Filter

Question

I am having trouble making my filters work with MongoDB .NET Driver, I get this error:

Unsupported filter: Invoke(value(System.Func2 [Role,System.Boolean]), {document}{Model}).

When trying to run this code:

public virtual async Task<PartitionedModel<T>> GetByAsync(Func<T, bool> filter)
{
    Expression<Func<PartitionedModel<T>, bool>> filt = (i) => filter(i.Model);
    PartitionedModel<T> item = (await collection.FindAsync(filt)).FirstOrDefault();
    return item;
}

and the class PartitionedModel look like this:

public class PartitionedModel<T> where T : IModel
{
    public ObjectId Id { get; set; }
    public PartitionOffset PartitionOffset { get; set; }
    public T Model { get; set; }
}

I did a refacto of my code working from having collections handling IModel directly to working with PartitionedModel which is a holding class for my IModel , the GetByAsync function worked correctly before I subclassed IModel

I found little to no informations about this problem except this: Dynamic Linq Predicate throws "Unsupported Filter" error with C# MongoDB Driver

But it seems like my version of the MongoDB C# Driver doesnt accept Func<> in parameter as filter, I can only pass Builder<> or Expression<> as a filter into the Find functions

Can someone enlighten me a bit about this error?

EDIT:

I tried to run this code by replacing the FindAsync(filt) with FindAsync(_ => true) and it actually works

Also, here is the code that is used to retrieve the collection

protected readonly IMongoCollection<PartitionedModel<T>> collection;

public GenericRepository(IMongoDatabase dbContext, string collectionName)
{
    collection = dbContext.GetCollection<PartitionedModel<T>>(collectionName);
}

and the version of my driver seems to be 2.7.0

EDIT 2: I've made my query works using this:

PartitionedModel<T> item = collection.AsQueryable().FirstOrDefault(filt);

But i'm not sure what is the implication of using a non-async version, can anyone tell me if this is wrong or if this will be a problem?

Answer 1

Seems like current implementation of c# mongo driver is not supported delegate-based filters.

https://github.com/mongodb/mongo-csharp-driver/blob/da0cff54c67208d979b030abb160f958d3276925/src/MongoDB.Driver/Linq/Translators/PredicateTranslator.cs#L76

The switch doesn't contain a ExpressionType.Invoke (the type of expression in delegate-based filter) case.

Answer 2

Mongo doesn't work with invocation filters. You can pass that invocation filter to LINQKit's expression expander and it will replace it with a predicate that the Mongo driver can then fully understand.

Magic is here

See it in action here