paging thru result from mongodb in C# code example

Example: paging thru result from mongodb in C#

public class Person
{
    [BsonId]
    [BsonRepresentation(BsonType.String)]
    public string Id { get; set; }

    public string FirstName { get; set; }

    public string Surname { get; set; }
}

public class Peger
{
    public int Count { get; set; }

    public int Page { get; set; }

    public int Size { get; set; }

    public IEnumerable Items { get; set; }
}

class Program
{
    static async Task Main(string[] args)
    {
        var client = new MongoClient();
        var database = client.GetDatabase("pager_test");
        var collection = database.GetCollection(nameof(Person));

        int page = 1;
        int pageSize = 5;
        var results = await GetPagerResultAsync(page, pageSize, collection);
    }

    private static async Task GetPagerResultAsync(int page, int pageSize, IMongoCollection collection)
    {
        // count facet, aggregation stage of count
        var countFacet = AggregateFacet.Create("countFacet",
            PipelineDefinition.Create(new[]
            {
                PipelineStageDefinitionBuilder.Count()
            }));

        // data facet, we’ll use this to sort the data and do the skip and limiting of the results for the paging.
        var dataFacet = AggregateFacet.Create("dataFacet",
            PipelineDefinition.Create(new[]
            {
                PipelineStageDefinitionBuilder.Sort(Builders.Sort.Ascending(x => x.Surname)),
                PipelineStageDefinitionBuilder.Skip((page - 1) * pageSize),
                PipelineStageDefinitionBuilder.Limit(pageSize),
            }));

        var filter = Builders.Filter.Empty;
        var aggregation = await collection.Aggregate()
            .Match(filter)
            .Facet(countFacet, dataFacet)
            .ToListAsync();

        var count = aggregation.First()
            .Facets.First(x => x.Name == "countFacet")
            .Output()
            ?.FirstOrDefault()
            ?.Count ?? 0;

        var data = aggregation.First()
            .Facets.First(x => x.Name == "dataFacet")
            .Output();

        return new Pager
        {
            Count = (int)count / pageSize,
            Size = pageSize,
            Page = page,
            Items = data
        };
    }
}