Is there a way to create a filter expression in MongoDB C# drivers (same way as projection allows)?-CodePudding

I can create a projection fiel definition from expression like that:

var projection = Builders<Bar>.Projection.Expression(x => x.Foo)

I want to do exactly the same with the filter:

var filter = Builders<Bar>.Filter.Expression(x => x.Foo == "10")

But I cannot find a way to do this. The operations that I want to perform FindOneAndUpdateAsync supports an expression as it's input directly, but I want to combine a "hardcoded" filter with the one that is coming in as a parameter. This is how I do it now without an expression:

var filter = Filter.Eq(x => x.Id, id); // Here I would like to write Filter.Expression(x => x.Id == id)
if (additionalFilter != null)
{
    filter &= additionalFilter;
}

P.S. I would rather avoid combining expressions directly "the C# way" as it is not very easy to understand.

CodePudding user response：

Mongo net driver does not support Filter.Expression and if you want to project any value cast to as ToList See the below eg:

 var filter = Builders<Movie>.Filter.In("cast", new string[] { "Tom Hanks" });
 var movies = await _moviesCollection.Find<Movie>(filter)
                .Limit(2)
                .ToListAsync();

// your test

var projection = Builders<Bar>.Projection.Expression(x => x.Foo);
    var projection = Builders<Bar>.Filter.Where(x => x.Foo == "10");