如何在ASP.NET Core Web API中在Azure Cosmos DB中实现上一个/下一个分页

Question

我需要支持Azure Cosmos DB的分页。我知道Cosmos DB可以在下一组结果上进行连续令牌。但是我不明白如何导航到以前的结果。

Answer 1

据我所知，从官方方式中，您只能基于连续令牌实施分页。您需要封装方法来实现这一点。

您可以参考@Nick撰写的文档。另外，您可以参考以下示例代码：

    private static async Task<KeyValuePair<string, IEnumerable<CeleryTask>>> QueryDocumentsByPage(int pageNumber, int pageSize, string continuationToken)
    {
        DocumentClient documentClient = new DocumentClient(new Uri("https://{CosmosDB/SQL Account Name}.documents.azure.com:443/"), "{CosmosDB/SQL Account Key}");
        var feedOptions = new FeedOptions {
            MaxItemCount = pageSize,
            EnableCrossPartitionQuery = true,
            // IMPORTANT: Set the continuation token (NULL for the first ever request/page)
            RequestContinuation = continuationToken 
        };
        IQueryable<CeleryTask> filter = documentClient.CreateDocumentQuery<CeleryTask>("dbs/{Database Name}/colls/{Collection Name}", feedOptions);
        IDocumentQuery<CeleryTask> query = filter.AsDocumentQuery();
        FeedResponse<CeleryTask> feedRespose = await query.ExecuteNextAsync<CeleryTask>();
        List<CeleryTask> documents = new List<CeleryTask>();
        foreach (CeleryTask t in feedRespose)
        {
            documents.Add(t);
        }
        // IMPORTANT: Ensure the continuation token is kept for the next requests
        return new KeyValuePair<string, IEnumerable<CeleryTask>>(feedRespose.ResponseContinuation, documents);
    }

然后，以下示例说明了如何通过调用上一个方法来检索给定页面的文档：

    private static async Task QueryPageByPage()
    {
        // Number of documents per page
        const int PAGE_SIZE = 3;
        int currentPageNumber = 1;
        int documentNumber = 1;
        // Continuation token for subsequent queries (NULL for the very first request/page)
        string continuationToken = null;
        do
        {
            Console.WriteLine($"----- PAGE {currentPageNumber} -----");
            // Loads ALL documents for the current page
            KeyValuePair<string, IEnumerable<CeleryTask>> currentPage = await QueryDocumentsByPage(currentPageNumber, PAGE_SIZE, continuationToken);
            foreach (CeleryTask celeryTask in currentPage.Value)
            {
                Console.WriteLine($"[{documentNumber}] {celeryTask.Id}");
                documentNumber++;
            }
            // Ensure the continuation token is kept for the next page query execution
            continuationToken = currentPage.Key;
            currentPageNumber++;
        } while (continuationToken != null);
        Console.WriteLine("n--- END: Finished Querying ALL Dcuments ---");
    }

顺便说一句，您可以在Cosmos DB反馈中遵循以下有关此功能的痕迹：

• https://github.com/azure/azure-documentdb-dotnet/issues/377
• https://feedback.azure.com/forums/263030-azure-cosmos-db/suggestions/6350987--documentdb-ablow-palla-palla-pagel-paging-skip-skip-take