如何在C# (MongoDB.Driver 2.7.2)中使用管道和let参数进行$lookup

using MongoDB.Driver;
using MongoDB.Bson;

var client = new MongoClient("mongodb://localhost:27017");
var database = client.GetDatabase("your_database_name");

var collection = database.GetCollection<BsonDocument>("your_collection_name");

var pipeline = new BsonDocument[]
{
    new BsonDocument("$lookup",
        new BsonDocument
        {
            { "from", "foreign_collection_name" },
            { "let", new BsonDocument("localField", "$localField") },
            { "pipeline", new BsonArray
                {
                    new BsonDocument("$match",
                        new BsonDocument("$expr",
                            new BsonDocument("$eq", new BsonArray { "$foreignField", "$$localField" }))
                    )
                }
            },
            { "as", "output_field_name" }
        }
    )
};

var result = collection.Aggregate<BsonDocument>(pipeline).ToList();