IDataStoreBase.RetrieveAsync(object[] arguments, CancellationToken cancellationToken) Method

.NET Standard 2.x

Asynchronously retrieves rows from the database.

Namespace: DWNet.Data

Assembly: DWNet.Data.dll

Syntax

public Task<int> RetrieveAsync(object[] arguments, CancellationToken cancellationToken)

Pararmeters

arguments System.Object[]

One or more values that you want to use as retrieval arguments in the SQL SELECT statement defined in the DataStore.

NOTE: This parameter is required.

cancellationToken CancellationToken

A cancellation token that can be used by other objects or threads to receive notice of cancellation.

Returns

Task<int>

Returns a task that represents the asynchronous operation.

Remarks

After rows are retrieved, the DataStore's filter is applied. Therefore, any retrieved rows that do not meet the filter criteria are immediately moved to the filter buffer and are not included in the return count.

Before you can retrieve rows for the DataStore, you must specify a DataContext object with the constructor of DataStore or SetDataContext method to establish a database connection.

Normally, when you call the RetrieveAsync method, any rows that are already in the DataStore are discarded and replaced with the retrieved rows. You can set DwRetrieveEventArgs.IsResetBuffer to false in the RetrieveStart event to prevent this. In this case, RetrieveAsync adds any retrieved rows to the ones that already exist in the buffers.

Events

The RetrieveAsync method triggers these events: RetrieveStart and RetrieveEnd.

None of these events is triggered if the data source is external, because RetrieveAsync always fails. You must use one of the import methods to populate the DataStore.

Examples

The following code example retrieves data asynchronously from the database. It uses a CancellationTokenSource type parameter to make this operation cancelable.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using DWNet.Data;

namespace Appeon.ApiDoc.IDataStoreBaseExamples
{
    public class RetrieveAsyncExample
    {
        private readonly SchoolContext _context;
        
        public RetrieveAsyncExample(SchoolContext dataContext)
        {
            // Sets the data context
            _context = dataContext;
        }

        public async Task<int> Example2(CancellationTokenSource cts)
        {
            // Instantiates a DataStore object with datawindow: d_department.
            var datastore = new DataStore("d_department", _context);
            
            int result = 0;
            
            try
            {
                // Retrieves rows from the database for datastore
                // If a task has been cancelled, the call to the 
                // DataStore.RetrieveAsync method throws an OperationCanceledException.
                result = await datastore.RetrieveAsync(2, cts.Token);
                
                Console.WriteLine("After Retrieve, Rowcount: {0}",
                    datastore.RowCount);
            }
            catch (OperationCanceledException e) 
            {
                // The operation was cancelled before completion.
                Console.WriteLine(e.Message);
            }
            catch (Exception e)
            {
                Console.WriteLine(e.Message);
            }
            finally 
            {
                cts.Dispose();
            }
            
            return result;
                    
            /*This code produces the following output:
             
                A task was canceled. 
            */
            
        }
    }
}

Example Refer To

Model Class: D_Department
DataWindow File: d_department

Applies to

.NET Standard

2.x