//--- Methods ---
private void PrepareRequest(bool fetchAllAttributes)
{
// inherit the expected types from the query select construct
foreach (var expectedType in _queryClause.TypeFilters)
{
_converter.AddExpectedType(expectedType);
}
// initialize request
_request.IndexName = _queryClause.IndexName;
_request.KeyConditionExpression = _queryClause.GetKeyConditionExpression(_converter);
_request.FilterExpression = _converter.ConvertConditions(_table.Options);
_request.ProjectionExpression = _converter.ConvertProjections();
// NOTE (2021-06-23, bjorg): the following logic matches the default behavior, but makes it explicit
// if `ProjectionExpression` is set, only return specified attributes; otherwise, for an index, return projected attributes only; for tables, return all attributes from each row
if (_request.ProjectionExpression is null)
{
if ((_request.IndexName is null) || fetchAllAttributes)
{
_request.Select = Select.ALL_ATTRIBUTES;
}
else
{
_request.Select = Select.ALL_PROJECTED_ATTRIBUTES;
}
}
public async Task <TRecord?> ExecuteAsync(CancellationToken cancellationToken)
{
_request.ProjectionExpression = _converter.ConvertProjections();
var response = await _table.DynamoClient.GetItemAsync(_request, cancellationToken);
return(response.IsItemSet
? _table.DeserializeItem <TRecord>(response.Item)
: null);
}
public async Task <IEnumerable <TRecord> > ExecuteAsync(int maxAttempts, CancellationToken cancellationToken = default)
{
var requestTableAndKeys = _request.RequestItems.First();
requestTableAndKeys.Value.ProjectionExpression = _converter.ConvertProjections();
// NOTE (2021-06-30, bjorg): batch operations may run out of capacity/bandwidth and may have to be completed in batches themselves
var result = new List <TRecord>();
var attempts = 1;
do
{
try {
var response = await _table.DynamoClient.BatchGetItemAsync(_request, cancellationToken);
if (response.Responses.Any())
{
foreach (var item in response.Responses.Single().Value)
{
var record = _table.DeserializeItem <TRecord>(item);
if (!(record is null))
{
result.Add(record);
}
}
}
// check if all requested primary keys were processed
if (!response.UnprocessedKeys.Any())
{
break;
}
// repeat request with unprocessed primary keys
requestTableAndKeys.Value.Keys = response.UnprocessedKeys.First().Value.Keys;
} catch (ProvisionedThroughputExceededException) {
// NOTE (2021-06-30, bjorg): not a single item could be returned due to insufficient read capacity
}
// use exponential backoff before attempting next operation
if (attempts >= maxAttempts)
{
throw new DynamoTableBatchGetItemsMaxAttemptsExceededException(result);
}
await Task.Delay(TimeSpan.FromMilliseconds(MILLISECOND_BACKOFF << (attempts++ - 1)));
} while(true);
return(result);
}