WPF CosmosDB ReadNextAsync() hangs when is calling in background_worker - wpf

Question

In WPF I have background_worker and in it I have to make request to Cosmos DB, request that use iterator:
_worker_GenerateReport.DoWork += _worker_GenerateReport_DoWork;
This is method for backgroundWorker:
void _worker_GenerateReport_DoWork(object sender, DoWorkEventArgs e)
var result = QueryItemsAsync2(connectionString, queryToDownloadData.ToString());
And method. In this method on GetAwaiter().GetResult(); it hangs:
private async Task<IEnumerable<DTO_Proj>> QueryItemsAsync2(
ConnectionString connectionString, string sqlQueryText)
{
QueryDefinition queryDefinition = new QueryDefinition(sqlQueryText);
var container = cosmosClient.GetContainer(connectionString.DatabaseID,
connectionString.Collection);
FeedIterator<DTO_Proj> resultSet =
container.GetItemQueryIterator<DTO_Proj>(queryDefinition,
requestOptions: new QueryRequestOptions()
{
//MaxItemCount = 1000,
MaxConcurrency = 1
});
while (resultSet.HasMoreResults)
{
Task<FeedResponse<DTO_Proj>> response = resultSet.ReadNextAsync();
var result = response.GetAwaiter().GetResult();
}
}
I have to write once again. I removed BackgroundWorker and I see that the problem is with fetching items from CosmosDB.
Now I have in xaml button:
<Button VerticalAlignment="Bottom" Grid.Row="1" HorizontalAlignment="Left" Command="{Binding Path=Command_GenerateReport2}" IsEnabled="{Binding Path=IsUIEnabled, UpdateSourceTrigger=PropertyChanged}">report2</Button>
in MVVM command is created as follow:
Command_GenerateReport2 = new MVVM.RelayCommand(p => Can_GenerateReport(), a => generateReport2());
Method generateReport2:
private void generateReport2()
{
ConnectionString connectionString = CreateConnectionStringAzureDB(serverToUse);
string queryTest = " SELECT * FROM c WHERE c.Proj = 2544912 ";
var result = QueryItemsAsync2(connectionString, queryTest);
}
And method QueryItemsAsync2:
private async Task<IEnumerable<DTO_Proj>> QueryItemsAsync2(ConnectionString connectionString, string sqlQueryText)
{
QueryDefinition queryDefinition = new QueryDefinition(sqlQueryText);
var container = cosmosClient.GetContainer(connectionString.DatabaseID, connectionString.Collection);
FeedIterator<DTO_Proj> resultSet = container.GetItemQueryIterator<DTO_Proj>(
queryDefinition,
requestOptions: new QueryRequestOptions()
{
MaxItemCount = 1000,
MaxConcurrency = 1
});
while (resultSet.HasMoreResults)
{
Task<FeedResponse<DTO_Proj>> response = resultSet.ReadNextAsync();
response.Wait();
...
And I have two CosmosDB containers. On one of them resultSet.ReadNextAsync() works and on the second hangs on this line. Configuration of these containers I think is the same. The difference is that on one container there is a lot of data and application hangs on it, on the second works but there is little data.

Answer 1

You should read the items asynchronously and not block by calling GetAwaiter().GetResult():
while (resultSet.HasMoreResults)
{
var item = await resultSet.ReadNextAsync();
...
}
Then you don't need to use a BackgroundWorker or involve any background threads. You could simply call and await the asynchronous QueryItemsAsync2 method:
var result = await QueryItemsAsync2(connectionString, queryToDownloadData.ToString());