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1 | | -# Web Reporting - Async Report Storage |
| 1 | +# How to Use the Asynchronous Engine for Web Reporting |
| 2 | + |
| 3 | +## Overview |
| 4 | +This example demonstrates how to use v20.2 services, which allow you to save, load, and export reports asynchronously. |
| 5 | +This application registers services with the **IReportProviderAsync** interface. The latter allows you to perform the following tasks asynchronously: |
| 6 | +- open subreports from the master report; |
| 7 | +- resolve a unique identifier to a report (an operation that affects the Designer Preview and Document Viewer performance). |
| 8 | +In general, asynchronous operation mode gives you the following advantages: |
| 9 | +- it handles threads in web applications more cautiously and returns threads to the thread pool while the operation is in progress. |
| 10 | +- You can write safe asynchronous code in a project with a third-party library that uses only asynchronous API. |
| 11 | + |
| 12 | +## Implementation Details |
2 | 13 |
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3 | | -Todo |
| 14 | +### Perequisites |
| 15 | + |
| 16 | +To get you started, we created a sample project with our ASP.NET Core Reporting Project Template. |
| 17 | + |
| 18 | +### Report Provider |
| 19 | + |
| 20 | +We declared a new code unit - `CustomReportProviderAsync.cs` with a class that implements the **DevExpress.XtraReports.Services.IReportProviderAsync** interface and calls the report storage's **GetDataAsync** method. |
| 21 | + |
| 22 | +### Report Storage |
| 23 | + |
| 24 | +To implement a custom report storage with asynchronous methods, we declared a new code unit - `CustomReportStorageWebExtension.cs`. The CustomReportStorageWebExtension class inherits from the [ReportStorageWebExtension](https://docs.devexpress.com/XtraReports/DevExpress.XtraReports.Web.Extensions.ReportStorageWebExtension) and overrides all its public methods. Note that methods, which cannot be used in asynchronous mode, throw exceptions. |
| 25 | + |
| 26 | +### Report Model and Controllers |
| 27 | + |
| 28 | +We used the **GetModelAsync** methods in the Home controller to generate report models and send them to the End User Report Designer and Document Viewer. |
| 29 | +ASP.NET Core Razor helpers cannot use asynchronous API if the Bind method receives a report instance or a string (ReportUrl) as a parameter. You must bind report controls to the [ReportDesignerModel](https://docs.devexpress.com/XtraReports/DevExpress.XtraReports.Web.ReportDesigner.ReportDesignerModel) or [WebDocumentViewerModel](https://docs.devexpress.com/XtraReports/DevExpress.XtraReports.Web.WebDocumentViewer.WebDocumentViewerModel) objects originated from controllers. The controller-based model allows you to use async API and avoid obscure problems. Such problems may occur when a subreport fails to load and throws an exception, or when a dynamic list of parameter values fails to retrieve its data. |
| 30 | + |
| 31 | +### ExportToPdf Action |
| 32 | + |
| 33 | +The export action takes advantage of the **IReportProviderAsync** service that resolves report ID to a report and expedites the load of subreports without the need for the web report controls. We used the DI container to inject the **IReportProviderAsync** service into the XtraReport instance. Then, we can call the asynchronous **CreateDocumentAsync** and **ExportToPdfAsync** methods. |
| 34 | + |
| 35 | +### Enable Asynchronous Services |
| 36 | + |
| 37 | +Request handlers in ASP.NET Core applications are asynchronous. To enable asynchronous services, we called the **UseAsyncEngine** method at application startup: |
| 38 | + |
| 39 | +```csharp |
| 40 | +services.ConfigureReportingServices(configurator => { |
| 41 | + configurator.ConfigureReportDesigner(designerConfigurator => { |
| 42 | + //.. |
| 43 | + }); |
| 44 | + configurator.ConfigureWebDocumentViewer(viewerConfigurator => { |
| 45 | + //.. |
| 46 | + }); |
| 47 | + configurator.UseAsyncEngine(); |
| 48 | +}); |
| 49 | +``` |
| 50 | + |
| 51 | +## Notes |
| 52 | + |
| 53 | +You can use an asynchronous engine in the following scenarios: |
| 54 | +- Handle the End User Report Designer and Web Document Viewer events to load data or create a document asynchronously. The key point is that these actions can be performed in the context of the current HTTP request in the [WebDocumentViewerOperationLogger](https://docs.devexpress.com/XtraReports/DevExpress.XtraReports.Web.WebDocumentViewer.WebDocumentViewerOperationLogger) and [PreviewReportCustomizationService](https://docs.devexpress.com/XtraReports/DevExpress.XtraReports.Web.ReportDesigner.Services.PreviewReportCustomizationService) class methods. |
| 55 | +- Drill Through navigation in the Web Document Viewer. Use the **IDrillThroughProcessorAsync** interface. |
| 56 | +- If an application uses JWT-based Authentication, use the **IWebDocumentViewerExportResultUriGeneratorAsync** interface to load exported documents to the storage asynchronously. |
| 57 | + |
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