Page through results

Runs the sample. Generated for this page; it reads the connection string from the environment and first remakes the sample database from sample-schema.json.

using ArxSamples.MongoDb;
using ArxSamples.MongoDb.Operations.RetrieveMultiple.Basics;

// The connection string comes from the environment, never from the code (see "Configure the connection").
var connectionString = Environment.GetEnvironmentVariable("ARX_SAMPLES_MONGODB")
    ?? throw new InvalidOperationException("Set the ARX_SAMPLES_MONGODB environment variable to your MongoDB connection string.");

var dbContext = new SampleContext(connectionString);

// Every run starts from the sample data: this deletes and makes again what sample-schema.json lists
// (save the file in the project folder, see Get started).
await dbContext.Direct.ResetAsync();

await new Basic2_PageThroughResults().RunAsync(dbContext);

The sample, as it is in the repository.

using ARX.SDK.MongoDb.Services;
using ARX.SDK.Query;
using ARX.SDK.Services;

using static ArxSamples.MongoDb.SampleOutput;

namespace ArxSamples.MongoDb.Operations.RetrieveMultiple.Basics;

/// <summary>
/// Page through a result, in two scenarios: by page number with the total, and by the paging cookie each page returns.
/// </summary>
/// <remarks>
/// A page number skips the earlier documents on the server; the total comes in the same round trip. A cookie says
/// where the next page starts (the last document's sort values and id), so no document is skipped or read twice even
/// when values repeat; pass it back unchanged, with the same query.
/// </remarks>
public sealed class Basic2_PageThroughResults : ISample
{
    public string Name => "retrieve-multiple-basics-2-page-through-results";

    public string Title => "Page through results";

    public async Task RunAsync(SampleContext dbContext)
    {
        var products = Enumerable.Range(1, 7).Select(i =>
        {
            var product = new ArxEntity("product");
            product["sku"] = $"SKU-M97{i}";
            product["name"] = $"Product {i}";
            product["category"] = "M97";
            product["price"] = i % 3 * 5m;
            return product;
        }).ToList();

        await dbContext.Service.CreateMultipleAsync(products);

        await Scenario1_ByPageNumberAsync(dbContext.Service);

        await Scenario2_ByCookieAsync(dbContext.Service);
    }

    private static ArxQueryExpression Category()
    {
        var query = new ArxQueryExpression("product");
        query.ColumnSet.AddColumns("name", "price");
        query.Criteria.AddCondition("category", ArxConditionOperator.Equal, "M97");
        query.AddOrder("price", ArxOrderType.Ascending);
        return query;
    }

    /// <summary>1. Page 2 of 3, with the total.</summary>
    private static async Task Scenario1_ByPageNumberAsync(ArxMongoDbService service)
    {
        Step("1. By page number");

        var query = Category();
        query.PageInfo = new ArxPagingInfo { Count = 3, PageNumber = 2, ReturnTotalRecordCount = true };

        var page = await service.RetrieveMultipleAsync(query);

        Show($"page {page.CurrentPage} of {page.TotalPageCount} ({page.TotalRecordCount} products): {string.Join(", ", page.Entities.Select(x => x["name"]))}");

        /* ===========================================================
         * [DIRECT QUERY CHECK]
         * -----------------------------------------------------------
         * db.product.countDocuments({ category: "M97" })
         * -- Expect: 7.
         * ===========================================================
         */
    }

    /// <summary>2. Every page by cookie: pass back the one the previous page gave, until there is none.</summary>
    private static async Task Scenario2_ByCookieAsync(ArxMongoDbService service)
    {
        Step("2. By cookie");

        string? cookie = null;
        var seen = new List<string>();

        do
        {
            var query = Category();
            query.PageInfo = new ArxPagingInfo { Count = 3, PagingCookie = cookie };
            var page = await service.RetrieveMultipleAsync(query);
            seen.AddRange(page.Entities.Select(x => (string)x["sku"]!));
            cookie = page.PagingCookie;
        }
        while (cookie != null);

        Show($"read {seen.Count} products, {seen.Distinct().Count()} different");

        /* ===========================================================
         * [DIRECT QUERY CHECK]
         * -----------------------------------------------------------
         * db.product.find({ category: "M97" }, { name: 1, price: 1 }).sort({ price: 1, _id: 1 })
         * -- Expect: 7 documents, in the order the pages read them.
         * ===========================================================
         */
    }
}

  > 1. By page number
      page 2 of 3 (7 products): Product 4, Product 7, Product 2
  > 2. By cookie
      read 7 products, 7 different