Fetch large results in batches. More...
Classes | |
| class | Cursor |
| Batch cursor for large query results. More... | |
A Cursor reads a query a batch at a time instead of loading every row into one Result. Obtain it from Statement::getCursor() with the number of rows per batch. It is a shared value: copying is cheap, and the backend cursor is closed when the last copy is destroyed or when close() is called.
Range-for walks every row and fetches the next batch when the current one is exhausted. That path is synchronous.
fetch() loads the next batch into the cursor's buffer and returns true while the batch is not empty. result() is that buffer, a Result with random access to the rows of the current batch only. When fetch() returns false, no more rows are available.
Asynchronous fetch needs a connection that was attached with setActive(). Connect to fetchFinished(), then call beginFetch(). In the slot, endFetch() returns the batch. isOpen() is true while the cursor can still produce rows; when it becomes false, the cursor has closed itself. Call beginFetch() again for the next batch while it stays open.
A cursor holds the statement's result stream. Do not run another operation on the same connection until the cursor is closed.