FederationDataSource.FillAsync(IEnumerable<IParameter>, CancellationToken) Method
Populates the FederationDataSource in an asynchronous manner, passes external parameters to the data source, and uses the cancellationToken parameter to send the cancellation signal.
Namespace: DevExpress.DataAccess.DataFederation
Assembly: DevExpress.DataAccess.v24.2.dll
Declaration
public Task FillAsync(
IEnumerable<IParameter> sourceParameters,
CancellationToken cancellationToken
)Parameters
| Name | Type | Description |
|---|---|---|
| sourceParameters | IEnumerable<IParameter> | External parameters passed to the data source. |
| cancellationToken | CancellationToken | A cancellation token that the task observes. |
Returns
| Type | Description |
|---|---|
| Task | A task that populates the data source. |
Remarks
Use this method to populate a federated data source in an individual task asynchronously. Unlike the Fill() method call, FillAsync does not lock other actions performed concurrently. For instance, the user interface remains operational while the data source is populated.
Call the FillAsync method with the await operator.
The sourceParameters parameter passes a collection of external parameters to the data source. For instance, you can pass report parameters from a reporting application and use report parameter values to filter data in the inner data sources.
The cancellationToken parameter provides a way to send the cancellation signal to the task. The task monitors the token and stops when it receives the signal. Create a CancellationTokenSource class instance and pass its Token property to the FillAsync method call. Call the CancellationTokenSource.Cancel method to stop the task.
Example
The code sample below creates a federated data source and binds the SQL data source query’s Category parameter to the CategoryID external parameter. A CancellationTokenSource class instance is used to allow users to interrupt the data source fill process if it takes too long.
using DevExpress.DataAccess;
using DevExpress.DataAccess.Sql;
using DevExpress.DataAccess.Excel;
using DevExpress.DataAccess.DataFederation;
using DevExpress.DataAccess.ObjectBinding;
using DevExpress.DataAccess.ConnectionParameters;
using System.IO;
using System.Threading;
// The cancellationTokenSource allows users to stop the task.
CancellationTokenSource cancellationTokenSource = new CancellationTokenSource();
// Creates and configures an SQL data source.
SqlDataSource sqlDataSource = new SqlDataSource(
new Access97ConnectionParameters(
Path.Combine(Path.GetDirectoryName(typeof(ReportCreator).Assembly.Location),
"Data/nwind.mdb"), "", ""))
{ Name = "Sql_Categories" };
var categoriesQuery = SelectQueryFluentBuilder
.AddTable("Categories")
.SelectAllColumnsFromTable()
.Filter("CategoryID=?Category")
.Build("Categories");
// Binds the "Category" query parameter to the "CategoryID" external parameter.
categoriesQuery.Parameters.Add(
new QueryParameter("Category",
typeof(Expression),
new Expression("?CategoryID")));
sqlDataSource.Queries.Add(categoriesQuery);
sqlDataSource.RebuildResultSchema();
// Creates and configures an Excel data source.
ExcelDataSource excelDataSource = new ExcelDataSource() { Name = "Excel_Products" };
excelDataSource.FileName = "Products.xlsx";
excelDataSource.SourceOptions = new ExcelSourceOptions()
{
ImportSettings = new ExcelWorksheetSettings("Sheet"),
};
excelDataSource.RebuildResultSchema();
// Creates and configures a federated data source.
FederationDataSource federationDataSource = new FederationDataSource();
Source sourceCategories = new Source(sqlDataSource.Name, sqlDataSource, "Categories");
Source sourceProducts = new Source(excelDataSource.Name, excelDataSource, "Products");
SelectNode selectNode = sourceCategories.From().Select("CategoryName")
.Join(sourceProducts, "[Excel_Products.CategoryID] = [Sql_Categories.CategoryID]")
.Select("CategoryID", "ProductName", "UnitPrice")
.Build("CategoriesProducts");
federationDataSource.Queries.Add(selectNode);
// Populates the data source's CategoriesProducts query.
await federationDataSource.FillAsync(
new[] { new Parameter("CategoryID", typeof(System.Int32), 4) },
cancellationTokenSource.Token);