集計

// Defines a queryable collection object as a prerequisite to using LINQ
var queryableCollection = collection.AsQueryable();
// Defines the query with $match and $group stages
var query = queryableCollection
    .Where(r => r.Cuisine == "Bakery")
    .GroupBy(r => r.Borough)
    .Select(g => new { _id = g.Key, Count = g.Count() });
// Executes the query and prints the aggregated results
foreach (var result in query.ToList())
{
    Console.WriteLine(result);
}

// Defines the $match aggregation stage  
var matchFilter = Builders<Restaurant>.Filter.Eq(r => r.Cuisine, "Bakery");
// Defines the aggregation pipeline with the $match and $group aggregation stages
var pipeline = new EmptyPipelineDefinition<Restaurant>()
    .Match(matchFilter)
    .Group(r => r.Borough,
        g => new
            {
                _id = g.Key,
                Count = g.Count()
            }
    );
// Executes the aggregation pipeline
var results = collection.Aggregate(pipeline).ToList();
// Prints the aggregated results
foreach (var result in results)
{
    Console.WriteLine(result);
}

// Defines the $match and $group aggregation stages
var matchStage = new BsonDocument
{
    {
        "$match",
        new BsonDocument
        {
            { "cuisine", "Bakery" }
        }
    }
};
var groupStage = new BsonDocument
{
    {
        "$group",
        new BsonDocument
        {
            { "_id", "$borough" },
            { "count", new BsonDocument("$sum", 1) }
        }
    }
};
// Executes the aggregation pipeline
var pipeline = new[] { matchStage, groupStage };
var results = collection.Aggregate<BsonDocument>(pipeline).ToList();
// Prints the aggregated results
foreach (BsonDocument result in results)
{
    Console.WriteLine(result);
}