MongoDb C# Driver Issue when trying to filter by enum value

Question

I need some help, I'm new to MongoDb, and using the 2.4.4 MongoDb.Driver for .Net.

I've created a class to strongly type my collection and one of its fields is an enum, I've managed to make the query return a string instead of an int on that field when using find by adding a BsonRepresentation decorator.

My current issue is when trying to filter by that enum field, I'm trying to do the following:

return await _context.Contacts
    .Find(x=> x.EnumField.ToString().Contains(searchTextParam)).ToListAsync();

So that I can filter by that field's text value, but that's throwing a runtime error:

System.ArgumentException: Unsupported filter: {document}{EnumField}.ToString().Contains("searchValue").

Thanks in advance, Jorge

Answer 1

Generally speaking, the LINQ integration in the driver does not support any and every kind of LINQ statement, and in my experience, using .ToString() on a property is one of those scenarios that is not supported (ie cannot be parsed by the driver to be converted into a MongoDB query).

Taking inspiration from https://stackoverflow.com/a/34033905/159446 , you might want to do something like this:

// assuming your class is also called Contacts
var filter = Builders<Contacts>.Filter.Regex(x => x.EnumField, 
              BsonRegularExpression.Create(searchTextParam));
return await _context.Contacts
     .Find(filter).ToListAsync();