/// <summary>
/// Run query definition into engine. Execute optimization to get query planner
/// </summary>
internal async Task <BsonDataReader> ExecuteQuery(bool executionPlan)
{
// get current transaction (if contains a explicit transaction) or a query-only transaction
var isNew = !_engine.HasTransaction();
var transaction = await _engine.GetTransaction();
//transaction.OpenCursors.Add(_cursor);
// return new BsonDataReader with IEnumerable source
return(await BsonDataReader.CreateAsync(RunQuery(), _collection));
async IAsyncEnumerable <BsonDocument> RunQuery()
{
var snapshot = await transaction.CreateSnapshot(_query.ForUpdate?LockMode.Write : LockMode.Read, _collection, false);
// no collection, no documents
if (snapshot.CollectionPage == null && _source == null)
{
// if query use Source (*) need runs with empty data source
if (_query.Select.UseSource)
{
yield return(_query.Select.ExecuteScalar(_pragmas.Collation).AsDocument);
}
transaction.OpenCursors.Remove(_cursor);
if (isNew)
{
_engine.ClearTransaction();
}
yield break;
}
// execute optimization before run query (will fill missing _query properties instance)
var optimizer = new QueryOptimization(snapshot, _query, _source, _pragmas.Collation);
var queryPlan = optimizer.ProcessQuery();
// if execution is just to get explan plan, return as single document result
if (executionPlan)
{
yield return(queryPlan.GetExecutionPlan());
transaction.OpenCursors.Remove(_cursor);
if (isNew)
{
_engine.ClearTransaction();
}
yield break;
}
// get node list from query - distinct by dataBlock (avoid duplicate)
var nodes = queryPlan.Index.Run(snapshot.CollectionPage, new IndexService(snapshot, _pragmas.Collation));
// get current query pipe: normal or groupby pipe
var pipe = queryPlan.GetPipe(transaction, snapshot, _pragmas);
try
{
// start cursor elapsed timer
_cursor.Elapsed.Start();
// call safepoint just before return each document
await foreach (var doc in pipe.Pipe(nodes, queryPlan))
{
_cursor.Fetched++;
_cursor.Elapsed.Stop();
yield return(doc);
if (transaction.State != TransactionState.Active)
{
throw new LiteException(0, $"There is no more active transaction for this cursor: {_cursor.Query.ToSQL(_cursor.Collection)}");
}
_cursor.Elapsed.Start();
}
}
finally
{
// stop cursor elapsed
_cursor.Elapsed.Stop();
transaction.OpenCursors.Remove(_cursor);
if (isNew)
{
_engine.ClearTransaction();
}
}
};
}